The SEP-IRA Over-Contribution Trap: Why Excess Self-Employed Retirement Contributions Draw a 10% Excise Tax Under §4972 — And Sometimes a 6% IRA Penalty Under §4973

Published: October 2, 2026 · Reading time: 15 min

TL;DR: A SEP-IRA contribution is legally an employer contribution to a "qualified employer plan" — IRC §4972(d)(1)(A)(iii) says so explicitly — so when a self-employed filer contributes more than the IRC §404(h)(1)(C) deduction limit allows (easy to do when the contribution is sized off an estimated Schedule C net profit before year-end), the excess draws a flat 10% excise tax under §4972(a), reported on Form 5330 and paid by the filer as employer — unconditionally, on whatever's still nondeductible at year-end. That's not necessarily the only tax in play: IRC §402(h)(2) treats the same excess dollars as "distributed" to the employee and as the employee's own IRA contribution once they exceed the SEP limit — but IRC §4973(b)(1) only taxes that recharacterized amount at 6% a year to the extent it, combined with any other personal IRA contributions made that year, exceeds the §219(b)(5)(A) personal-IRA deduction limit ($7,500 for 2026). That condition is the part almost every "excess retirement contribution" article skips. In the worked example below, a freelance web developer who contributes $27,880.57 in December based on a $150,000 profit estimate, then finalizes 2026 at $122,000 net profit after a December Section 179 equipment purchase, ends up with a $5,204.38 nondeductible contribution: a verified $520.44 excise tax under §4972 that applies regardless — and, because this filer made no other personal IRA contribution in 2026, the full $7,500 of §219 room absorbs the entire $5,204.38 recharacterized amount, so the §4973 tax for this filer is $0. Use up that same $7,500 of room with other IRA contributions instead, and the identical $5,204.38 draws a $312.26-a-year §4973 tax with no offset left to shrink it — a combined $832.70 of first-year exposure in that scenario, versus just the $520.44 §4972 tax alone in the filer's actual case. The §4972 side isn't lost money either way (§404(h)(1)(C) lets it carry forward and become deductible later), and whatever §4973 tax does exist can be stopped with a "withdraw it by the filing deadline" fix under §408(d)(4), just on a later deadline than Form 5330's. Skip that withdrawal where it's needed, and claim a full fresh contribution the following year rather than deliberately leaving room, and the same $520.44 §4972 tax applies again, regardless of how the §4973 side played out.

Nearly every piece of SEP-IRA content aimed at freelancers states the contribution limit the same simplified way: "up to 25% of your net profit, capped at [this year's dollar limit]." That's close enough for sizing a contribution with a comfortable buffer. It's the wrong formula once a number gets tight — and it says nothing at all about what happens if the number you funded the SEP with turns out to be too high once your books are actually closed. That second question is this guide's entire subject.

Why "25% of Net Profit" Already Isn't Your Limit

A SEP's plan document states a flat contribution rate — commonly 25%, the maximum IRC §404(h)(1)(C) allows a defined-contribution plan to deduct: "[t]he amount deductible in a taxable year for a simplified employee pension shall not exceed 25 percent of the compensation paid to the employees during the calendar year ending with or within the taxable year...." For a common-law employee, that 25% applies straightforwardly to their W-2 compensation. For the business owner contributing for themselves, it doesn't, because of how "compensation" is defined for a self-employed person.

IRC §404(a)(8)(B) states that for a self-employed individual, "the term 'earned income' has the meaning assigned to it by section 401(c)(2)." And §401(c)(2)(A) defines earned income as net earnings from self-employment, computed "with regard to the deductions allowed by section 404 to the taxpayer, and ... with regard to the deduction allowed to the taxpayer by section 164(f)" — that is, after subtracting both the deduction for half of self-employment tax and the retirement plan contribution itself. The contribution is being computed as a percentage of a number that already has the contribution subtracted out of it — a circular definition that has to be solved algebraically rather than applied directly.

IRS Publication 560 solves it for you with the Rate Table for Self-Employed, which converts a stated 25% plan rate into an effective rate of exactly:

"25* 0.200000* * The deduction for annual employer contributions (other than elective deferrals) to a SEP plan, a profit-sharing plan, or a money purchase pension plan can't be more than 20% of your net earnings (figured without deducting contributions for yourself) from the business that has the plan."

(The table's "25" is the plan's stated contribution rate in percent, from a column headed "shown as %"; "0.200000" in the next column is the resulting self-employed rate as a decimal — the 20% figure the footnote then states in words.)

So the real formula is roughly 20% of (net profit minus half your self-employment tax) — not 25% of raw net profit, and not even 20% of raw net profit. The gap between "25% of net profit" (the shorthand) and "20% of net profit after the SE-tax deduction" (the actual rule) is modest at most income levels, but it's exactly the kind of gap that turns a contribution sized off a rough estimate into an over-contribution once the real numbers are in.

The 2026 Dollar Limits, Verified Directly

Two caps sit on top of the percentage formula, both adjusted annually for inflation. IRS Notice 2025-67 states:

"The limitation for defined contribution plans under section 415(c)(1)(A) is increased in 2026 from $70,000 to $72,000."

and

"The annual compensation limitation under sections 401(a)(17), 404(l), 408(k)(3)(C), and 408(k)(6)(D)(ii) is increased from $350,000 to $360,000."

For 2026, that means: the effective-rate percentage calculation, capped at $72,000 outright, and separately capped by 25% of whichever is smaller — your actual compensation or $360,000. Both caps are irrelevant at the income level in the worked example below (neither one binds), but checking that they don't bind is itself part of doing the computation correctly, not an optional step to skip because they usually don't matter.

Why the 10% Tax Doesn't Rule Out the 6% Tax — But the 6% Isn't Automatic Either

Content on "excess retirement contributions" almost universally describes one mechanism: IRC §4973(a) imposes, for several types of accounts including "an individual retirement account (within the meaning of section 408(a))," "a tax in an amount equal to 6 percent of the amount of the excess contributions to such individual's accounts or annuities (determined as of the close of the taxable year)." Section 4973(b) defines that excess by reference to "the amount allowable as a deduction under section 219" — the ordinary personal-IRA deduction. That's the rule built for someone who contributes too much to their own traditional or Roth IRA, and it's genuinely a different rule from the one that taxes the employer's nondeductible SEP contribution below. "Different rule," though, doesn't mean "mutually exclusive" — and a SEP-IRA turns out to be a bad candidate for that assumption. It's also a bad candidate for the opposite assumption, that the two regimes simply stack: the §219 reference baked into §4973(b)'s own definition is what makes the second tax's reach conditional on something outside the SEP entirely — how much of your personal IRA deduction room is already used up.

A SEP-IRA contribution is, first, an employer contribution under IRC §408(k). IRC §4972(d)(1)(A) defines "qualified employer plan" — the category §4972's excise tax applies to — as:

"(i) any plan meeting the requirements of section 401(a) which includes a trust exempt from tax under section 501(a), (ii) an annuity plan described in section 403(a), (iii) any simplified employee pension (within the meaning of section 408(k)), and (iv) any simple retirement account (within the meaning of section 408(p))."

A SEP is named explicitly, in clause (iii). IRC §4972(a) then imposes "a tax equal to 10 percent of the nondeductible contributions under the plan (determined as of the close of the taxable year of the employer)" — and §4972(b) makes clear who pays it: "[t]he tax imposed by this section shall be paid by the employer making the contributions." For a sole proprietor, that's you, in your capacity as your own employer — IRC §401(c)(4) states plainly that "[a]n individual who owns the entire interest in an unincorporated trade or business shall be treated as his own employer." You're both employer and employee under this plan, and it's the employer half of you that owes this tax.

But the same account is also, independently, something §4973 reaches directly. IRC §408(k)(1) defines a "simplified employee pension" as, itself, "an individual retirement account or individual retirement annuity" that merely satisfies a handful of extra requirements — which means a SEP-IRA is an account "within the meaning of section 408(a)," the exact phrase §4973(a) uses. Being named as a "qualified employer plan" under §4972 doesn't un-name it as an "individual retirement account" under §4973; the two labels describe the same dollars in the same account from two different angles, and the code taxes both angles.

The connective tissue is IRC §402(h). Ordinarily, §402(h)(1) excludes an employer's SEP contribution from the employee's gross income entirely — which is why a properly sized SEP contribution produces no §4973 exposure at all. §402(h)(2) is the exception that matters here: "Contributions made by an employer to a simplified employee pension with respect to an employee for any year shall be treated as distributed or made available to such employee and as contributions made by the employee" to the extent they exceed the SEP's own limit — precisely the circumstance in the worked example below. IRS Publication 560 states the consequence in plain English for the self-employed case specifically: "Excess contributions are included in the employee's income for the year and are treated as contributions by the employee to their SEP IRA," directing the reader to Publication 590-A — the ordinary personal IRA publication — "for more information on employee tax treatment of excess contributions."

Once that recharacterization happens, §4973(b)(1) does the rest of the work — and this is where the mechanism stops being automatic in either direction. §4973(b)(1)(A) defines "excess contributions" as the amount contributed to the account — explicitly carving out only "a contribution to a Roth IRA or a rollover contribution," nothing about SEP contributions — minus, per subparagraph (B), "the amount allowable as a deduction under section 219." The subsection's own flush language adds that this §219 amount is computed "without regard to section 219(g)" — the active-participant phase-out that would otherwise shrink or zero out a SEP participant's personal IRA deduction at higher income, and that disregard matters precisely because a SEP participant nearly always is an active participant.

For an ordinary, within-limit SEP contribution, IRC §408(d)(7)(B) treats the excludable §402(h) amount as if it were itself a §219 deduction, so the subtraction nets to zero and nothing is "excess" for §4973 purposes — which is why a properly sized SEP produces no §4973 exposure at all. The over-the-limit portion that §402(h)(2) recharacterizes as the employee's own contribution gets no such automatic offset — but it isn't automatically taxed either. Once recharacterized, it's an ordinary personal IRA contribution for §219 purposes, competing for the same $7,500 (2026) deduction room under §219(b)(5)(A) that any other personal IRA contribution draws on. (IRC §219(b)(2)'s carve-out — "[t]his section shall not apply with respect to an employer contribution to a simplified employee pension" — describes the employer's contribution; it doesn't apply to the recharacterized amount, which §402(h)(2) has already relabeled as the employee's own.) Whether that $7,500 of room is available depends on what else the filer contributed to a personal IRA that year: use none of it elsewhere, and the full $7,500 offsets the recharacterized excess dollar-for-dollar under §4973(b)(1)(B), leaving nothing to tax at 6%. Use all of it elsewhere — on an independent traditional or Roth IRA contribution — and the recharacterized excess gets no offset at all, so the full amount becomes a §4973 "excess contribution," taxed at 6% a year until corrected. The $5,204.38 nondeductible employer contribution under §4972(c)(1)(A) is, in every case, taxed once under §4972; whether it's also an excess IRA contribution of the employee under §4973(b)(1)(A) depends on that $7,500 offset, not on recharacterization alone. See the worked example below for both outcomes on the identical dollars.

Worked Example: A December Contribution, a January Surprise

Facts. Jordan is a single freelance web developer with no employees, running a SEP-IRA with a plan document that states the maximum 25% contribution rate. In late November 2026, with eleven months of actual books closed and one month of projected revenue left, Jordan estimates full-year net profit at $150,000 and wires the maximum SEP contribution that estimate supports before year-end. In December, Jordan also buys $28,000 of equipment for the business and fully expenses it, which — combined with a slower-than-projected December — brings Jordan's actual, final 2026 Schedule C net profit down to $122,000. Jordan makes no other personal traditional or Roth IRA contribution at any point during 2026 — a fact that turns out to matter.

node -e "
// ============================================================
// IRC Sec.404(h)(1)(C) / Sec.401(c)(2) self-employed SEP deduction worksheet
// Dollar limits per IRS Notice 2025-67 (2026): Sec.415(c)(1)(A) = \$72,000,
// Sec.401(a)(17)/408(k)(3)(C) compensation cap = \$360,000.
// ============================================================
function r(x){return Math.round(x*100)/100}
const SEP_EFFECTIVE_RATE = 0.200000; // Pub. 560 Rate Table for Self-Employed, 25% plan-rate row
const COMP_CAP_2026 = 360000;
const DC_DOLLAR_LIMIT_2026 = 72000;
const PLAN_STATED_RATE = 0.25;

function worksheet(netProfit) {
  const earnings = r(netProfit * 0.9235);
  const seTax = r(earnings * 0.153);
  const half = r(seTax / 2);               // Step 2 -- half-SE-tax above-the-line deduction
  const netSE = r(netProfit - half);        // Step 3 -- net earnings from self-employment
  const pctRoom = r(netSE * SEP_EFFECTIVE_RATE); // Step 5
  const compCapRoom = r(COMP_CAP_2026 * PLAN_STATED_RATE); // Step 6
  const maxDeductible = Math.min(pctRoom, compCapRoom, DC_DOLLAR_LIMIT_2026); // Step 7/8/21
  return { netProfit, earnings, seTax, half, netSE, pctRoom, compCapRoom, maxDeductible };
}

console.log('=== November estimate, used to size the December contribution ===');
const est = worksheet(150000);
console.log(est);
console.log('Jordan contributes the full amount the estimate supports:', est.maxDeductible);
console.log();

console.log('=== Actual, final 2026 results (after the December Sec.179 equipment purchase) ===');
const act = worksheet(122000);
console.log(act);
console.log();

const contributed = est.maxDeductible;
const excess = r(contributed - act.maxDeductible);
console.log('Amount actually contributed in December:', contributed);
console.log('Actual 2026 maximum deductible SEP contribution:', act.maxDeductible);
console.log('Nondeductible (excess) contribution, Sec.4972(c)(1)(A):', excess);

const tax4972 = r(excess * 0.10);
console.log('Sec.4972(a) excise tax for 2026 (10%, Form 5330 Schedule A, employer side, UNCONDITIONAL):', tax4972);

// Sec.4973(b)(1): excess IRA contribution = amount contributed minus the amount
// allowable as a deduction under Sec.219 -- here, the recharacterized Sec.402(h)(2)
// amount competes for the SAME Sec.219(b)(5)(A) personal-IRA room as any other
// personal IRA contribution the filer makes that year.
const PERSONAL_IRA_LIMIT_2026 = 7500; // Sec.219(b)(5)(A), per IRS Notice 2025-67

console.log();
console.log('=== Sec.4973 exposure is CONDITIONAL on Jordan\'s OTHER personal IRA contributions for 2026 ===');

console.log('--- Case 1 (the actual facts): Jordan made NO other personal IRA contribution in 2026 ---');
const otherIRA1 = 0;
const room1 = r(PERSONAL_IRA_LIMIT_2026 - otherIRA1);
const offset1 = Math.min(excess, room1);
const sec4973Excess1 = r(excess - offset1);
const tax4973Case1 = r(sec4973Excess1 * 0.06);
console.log('Sec.219(b)(5)(A) room available to offset the recharacterized excess:', room1);
console.log('Sec.4973(b)(1) excess contribution after the offset:', sec4973Excess1);
console.log('Sec.4973(a) tax for 2026:', tax4973Case1);

console.log();
console.log('--- Case 2 (hypothetical): Jordan already used the full $7,500 on a separate personal IRA in 2026 ---');
const otherIRA2 = 7500;
const room2 = r(Math.max(0, PERSONAL_IRA_LIMIT_2026 - otherIRA2));
const offset2 = Math.min(excess, room2);
const sec4973Excess2 = r(excess - offset2);
const tax4973Case2 = r(sec4973Excess2 * 0.06);
console.log('Sec.219(b)(5)(A) room available to offset the recharacterized excess:', room2);
console.log('Sec.4973(b)(1) excess contribution after the offset:', sec4973Excess2);
console.log('Sec.4973(a) tax for 2026:', tax4973Case2);

console.log();
console.log('Combined first-year exposure, Case 1 (Jordan\'s actual facts):', r(tax4972 + tax4973Case1));
console.log('Combined first-year exposure, Case 2 (hypothetical, room already used):', r(tax4972 + tax4973Case2));
"

Output:

=== November estimate, used to size the December contribution ===
{
  netProfit: 150000,
  earnings: 138525,
  seTax: 21194.33,
  half: 10597.17,
  netSE: 139402.83,
  pctRoom: 27880.57,
  compCapRoom: 90000,
  maxDeductible: 27880.57
}
Jordan contributes the full amount the estimate supports: 27880.57

=== Actual, final 2026 results (after the December Sec.179 equipment purchase) ===
{
  netProfit: 122000,
  earnings: 112667,
  seTax: 17238.05,
  half: 8619.03,
  netSE: 113380.97,
  pctRoom: 22676.19,
  compCapRoom: 90000,
  maxDeductible: 22676.19
}

Amount actually contributed in December: 27880.57
Actual 2026 maximum deductible SEP contribution: 22676.19
Nondeductible (excess) contribution, Sec.4972(c)(1)(A): 5204.38
Sec.4972(a) excise tax for 2026 (10%, Form 5330 Schedule A, employer side, UNCONDITIONAL): 520.44

=== Sec.4973 exposure is CONDITIONAL on Jordan's OTHER personal IRA contributions for 2026 ===
--- Case 1 (the actual facts): Jordan made NO other personal IRA contribution in 2026 ---
Sec.219(b)(5)(A) room available to offset the recharacterized excess: 7500
Sec.4973(b)(1) excess contribution after the offset: 0
Sec.4973(a) tax for 2026: 0

--- Case 2 (hypothetical): Jordan already used the full $7,500 on a separate personal IRA in 2026 ---
Sec.219(b)(5)(A) room available to offset the recharacterized excess: 0
Sec.4973(b)(1) excess contribution after the offset: 5204.38
Sec.4973(a) tax for 2026: 312.26

Combined first-year exposure, Case 1 (Jordan's actual facts): 520.44
Combined first-year exposure, Case 2 (hypothetical, room already used): 832.7

Both the $90,000 compensation-cap room (25% of the $360,000 2026 cap) and the flat $72,000 dollar limit sit well above the 20%-of-net-SE-earnings figure in both scenarios, so neither one binds here — the percentage formula is what actually controls, which is the ordinary case for a business at this income level. Jordan's December contribution of $27,880.57 exceeds the actual, final deduction limit of $22,676.19 by $5,204.38. That $5,204.38 is a nondeductible SEP contribution under §4972(c)(1)(A), owing a $520.44 excise tax for 2026 under §4972 — unconditionally, regardless of anything else on Jordan's return.

Whether it also draws the §4973 6%-per-year tax is a separate question with a separate answer, because the same $5,204.38 is simultaneously recharacterized as Jordan's own IRA contribution under §402(h)(2) — and §4973(b)(1) taxes that recharacterized amount only to the extent it, combined with any other personal IRA contributions Jordan made for 2026, exceeds the $7,500 (2026) §219(b)(5)(A) personal-IRA deduction limit. Jordan made no other personal IRA contribution that year, so the full $7,500 of room is unused and absorbs the entire $5,204.38 — Jordan's own §4973 exposure for 2026 is $0. That's the actual answer for this worked example, and it's worth sitting with: the second tax almost every "excess contribution" explainer treats as automatic simply doesn't apply here, because the offset in §4973(b)(1)(B) fully consumes the recharacterized amount.

Had Jordan instead already contributed the full $7,500 to a separate traditional or Roth IRA that same year — leaving no §219 room to spare — the identical $5,204.38 would get no offset at all, and §4973 would tax the whole thing: a $312.26-per-year charge that keeps accruing until corrected, for a combined $832.70 of first-year exposure in that scenario, versus Jordan's actual $520.44 alone. The lesson isn't "the 6% tax never applies to a SEP excess" — it's "check your own Schedule 1 IRA deduction before assuming either way." A filer who already maxes a personal IRA alongside their SEP — common enough — gets no benefit of the doubt here; Jordan got lucky only because that $7,500 of room happened to be sitting unused. Wherever a §4973 tax does apply, it can be stopped by withdrawing the excess (plus earnings) under IRC §408(d)(4) by the filer's own extended filing deadline (October 15, 2027 for 2026) — a different, later deadline than Form 5330's July 31 — though that withdrawal doesn't touch the §4972 tax already accrued, and it gives up the §404(h)(1)(C) carryforward on those dollars since they're no longer in the plan. See the FAQ above for how the two corrective paths differ.

What Happens the Following Year: Carryforward, or the Same Tax Again

The $5,204.38 isn't gone. IRC §404(h)(1)(C) states that the excess "shall be deductible in the succeeding taxable years in order of time, subject to the 25 percent limit..." — so once 2027 has unused room under the same effective-rate ceiling, the carried-over amount becomes deductible then, with no new contribution required. But that room is shared with whatever fresh contribution Jordan makes for 2027, and how Jordan splits it determines whether the §4972 tax ever applies again. This whole carryforward mechanism is specific to the §4972 side, and it runs regardless of what happens on the §4973 side — which, as the worked example above shows, is $0 for Jordan's actual facts. For a filer whose §4973 tax isn't zero (because their other-IRA room was already used up), the same point still holds: if they didn't withdraw the excess under §408(d)(4) by the return's extended due date, that 6%-per-year tax keeps running on its own schedule regardless of how the §4972 carryforward plays out — leaving it in the plan to chase a future §404(h)(1)(C) deduction and racking up another year of §4973 exposure are the same decision, not two separate ones, for anyone in that position.

node -e "
function r(x){return Math.round(x*100)/100}
const SEP_EFFECTIVE_RATE = 0.200000;
const COMP_CAP_PROXY = 360000;  // 2027 figures not yet published; 2026 figures used as the best available proxy
const DC_LIMIT_PROXY = 72000;
const PLAN_STATED_RATE = 0.25;

function room(netProfit) {
  const earnings = r(netProfit * 0.9235);
  const seTax = r(earnings * 0.153);
  const half = r(seTax / 2);
  const netSE = r(netProfit - half);
  const pctRoom = r(netSE * SEP_EFFECTIVE_RATE);
  const compCapRoom = r(COMP_CAP_PROXY * PLAN_STATED_RATE);
  return Math.min(pctRoom, compCapRoom, DC_LIMIT_PROXY);
}

const carryover = 5204.38; // the 2026 nondeductible contribution carried under Sec.404(h)(1)(C)
const NET_PROFIT_2027 = 135000; // illustrative
const totalRoom2027 = room(NET_PROFIT_2027);
console.log('2027 total deduction room (illustrative dollar limits):', totalRoom2027);

console.log();
console.log('--- Scenario A: Jordan deliberately under-contributes fresh money to leave room ---');
const freshSized = r(totalRoom2027 - carryover);
console.log('Fresh 2027 contribution Jordan makes:', freshSized);
console.log('Total deducted for 2027 (fresh + absorbed carryover):', r(freshSized + carryover));
console.log('Nondeductible balance as of close of 2027:', r(carryover - carryover));
console.log('2027 Sec.4972(a) excise tax:', r((carryover - carryover) * 0.10));

console.log();
console.log('--- Scenario B: Jordan instead contributes the FULL fresh 2027 room, as usual ---');
console.log('Fresh 2027 contribution:', totalRoom2027, '-- leaves $0 of room for the carryover');
console.log('Carryover still nondeductible as of close of 2027:', carryover);
console.log('2027 Sec.4972(a) excise tax (the SAME excess, taxed again):', r(carryover * 0.10));
"

Output:

2027 total deduction room (illustrative dollar limits): 25092.51

--- Scenario A: Jordan deliberately under-contributes fresh money to leave room ---
Fresh 2027 contribution Jordan makes: 19888.13
Total deducted for 2027 (fresh + absorbed carryover): 25092.51
Nondeductible balance as of close of 2027: 0
2027 Sec.4972(a) excise tax: 0

--- Scenario B: Jordan instead contributes the FULL fresh 2027 room, as usual ---
Fresh 2027 contribution: 25092.51 -- leaves $0 of room for the carryover
Carryover still nondeductible as of close of 2027: 5204.38
2027 Sec.4972(a) excise tax (the SAME excess, taxed again): 520.44

Three things worth noticing:

1. "Carries forward" means the excess competes for next year's room — it doesn't get its own separate bucket. In Scenario A, Jordan contributes $19,888.13 of new money for 2027 — $5,204.38 less than 2027's own $25,092.51 room would otherwise allow — specifically so that the leftover room absorbs the 2026 carryover. Total deducted for 2027 is the full $25,092.51, the carryover's nondeductible balance drops to $0, and no further excise tax applies.

2. Contributing normally the following year — the default, unthinking move — doesn't fix anything. In Scenario B, Jordan contributes the full $25,092.51 2027 room as a fresh contribution (the ordinary, maximize-every-year approach), leaving zero room for the $5,204.38 carryover. That amount is still nondeductible "as of the close of" 2027, and §4972(a) taxes it again: another $520.44, on the exact same dollars that were already taxed once for 2026. There's no limit in the statute on how many years in a row this can repeat if room is never deliberately freed up.

3. 2027's own dollar and compensation limits aren't published as of this post's date, so this scenario uses 2026's figures as an explicit stand-in — consistent with how this corpus handles a future year's not-yet-announced limits elsewhere. The mechanism (percentage room, shared between fresh contributions and carryover absorption) doesn't depend on which year's exact dollar caps apply; only the precise room figure would shift once 2027's inflation adjustments are published.

What This Doesn't Fix

• It doesn't change your QBI deduction math. A SEP or Solo 401(k) employer contribution reduces qualified business income dollar-for-dollar under Treas. Reg. §1.199A-3(b)(1)(vi), the same way it does when sized correctly — getting the contribution amount wrong here also means your §199A computation was run on the wrong number until it's corrected. See the QBI deduction guide for how that deduction is actually capped.
• It doesn't retroactively change what you could have contributed. The $22,676.19 actual limit in the example is fixed by Jordan's real, final net profit — there's no mechanism to "true up" the limit itself, only the contribution against it.
• A properly sized SEP contribution doesn't touch your personal IRA room — but a recharacterized excess does. A within-limit SEP contribution is excluded from your income under §402(h)(1) and, per IRC §408(d)(7)(B), treated as if it were itself a §219 deduction — so it neither counts against nor draws down your separate personal traditional/Roth IRA contribution limit (IRC §219(b)(5)(A), $7,500 for 2026). The portion that exceeds the SEP limit is different: §402(h)(2) recharacterizes it as your own personal IRA contribution, and it then competes for that same $7,500 of §219 room against whatever else you contributed to a traditional or Roth IRA that year — exactly the mechanism the worked example above runs through. Size your SEP contribution correctly and this bullet is moot; over-contribute, and the excess portion is no longer independent of your personal IRA limit at all.
• It doesn't apply to a Solo 401(k)'s elective deferral the same way. As the FAQ above covers, the employee-deferral half of a Solo 401(k) is governed by §402(g), not §4972 — don't apply this guide's carryforward mechanics to that half of the plan.

Common Mistakes to Avoid

1. Sizing a December SEP contribution off a profit estimate with no buffer. A contribution calculated from the final, actual Schedule C net profit — even if that means waiting until closer to the filing deadline — can't create this problem; one calculated from a rough November projection can, especially if a late-year equipment purchase or other deduction still hasn't been booked.
2. Assuming "25% of net profit" is the real limit. It's the plan's stated rate, not the self-employed filer's actual deduction — the effective rate is closer to 20% of net profit after the deduction for half of self-employment tax, per the circular formula in §404(a)(8) and §401(c)(2).
3. Assuming an over-funded SEP's 6% exposure is either always-on or never-happens. A SEP contribution is an employer contribution under §408(k), explicitly listed under §4972(d)(1)(A)(iii) and drawing the 10% tax under §4972(a) unconditionally — that part never depends on anything else. But a SEP-IRA is also, by §408(k)(1)'s own definition, an "individual retirement account" under §408(a), and §402(h)(2) treats the excess portion as the employee's own contribution to it, subject to §4973(b)(1)'s offset against the filer's $7,500-for-2026 §219(b)(5)(A) personal-IRA deduction room just like any other personal IRA contribution. Whether the 6% tax actually applies depends on how much of that $7,500 of room the filer used up elsewhere that year: treat it as automatically "10% instead of 6%" and you'll under-report a real 6% liability when the room is already spoken for; treat it as automatically "10% and 6%, always" and you'll over-report a 6% liability the §219 offset already erased.
4. Assuming a withdrawal fixes nothing, or fixes everything. A withdrawal under §408(d)(4), done by your own extended filing deadline, stops whatever §4973 6%-per-year tax applies (see Mistake 3 for when that is, and when it's already $0) — that part of the personal-IRA playbook does transfer to a SEP excess. But it doesn't touch the separate §4972 tax: §4972(c)(1)(A) has no "returned to the employer" offset for the year the excess was created, and the only relief that exists, under §4972(c)(1)(B)(i), only ever reduces a later year's carryover, to the extent an amount is "available for return under the applicable qualification rules" of the specific plan. Confirm which (if either) your situation supports before assuming either outcome.
5. Contributing the full fresh amount the following year without leaving room for the carryover. Doing so re-triggers the same 10% tax on the same dollars, as Scenario B above shows — the carryover needs deliberately freed-up room, not just the passage of a year.
6. Confusing this with the SARSEP "excess SEP contribution" rule in Publication 560. That's a nondiscrimination-testing rule for highly compensated employees' elective deferrals in a legacy plan type closed to new adopters since 1996 — unrelated to an ordinary SEP's employer contribution exceeding its own deduction limit.
7. Filing only one of Form 5330 and Form 5329 when both may be owed. The §4972 tax on a nondeductible employer contribution goes on Form 5330, Schedule A, due well before the income tax return's own extended deadline — always, if there's a nondeductible contribution at all. If the §4973 side applies (see Mistake 3) and wasn't corrected under §408(d)(4) in time, that 6% tax goes separately on Form 5329 with your personal Form 1040 — filing one and assuming it covers the other misses whichever tax that form doesn't compute, and filing Form 5329 by default when the §219 offset already zeroed out the excess overstates a liability you don't have.

How CentSense Helps

CentSense doesn't run the self-employed SEP deduction worksheet or file Form 5330 — that's a computation your CPA or tax software handles once the final numbers are in — but it solves the part of this problem that actually causes it:

• Every receipt and expense is scanned and categorized as it happens, so a December equipment purchase (the kind that quietly resets your deduction room, as in the worked example) is already reflected in your running net profit the moment it's logged, not discovered during tax-season reconciliation
• A real-time view of year-to-date Schedule C profit means a SEP contribution can be sized off your actual, current numbers instead of a rough November projection
• Clean, dated records make it straightforward to see exactly how much a late-year purchase moved your net profit — the gap this entire mechanic depends on

For the mechanics this guide assumes elsewhere, see SEP-IRA vs. Solo 401(k) for choosing between the two plan types, Solo 401(k) Retroactive Adoption Deadline for how late a plan itself can be opened, Section 179 Deduction for Freelancers for the equipment-expensing mechanic that moved Jordan's net profit in this example, Self-Employment Tax Explained for the 92.35%/15.3% computation behind every figure above, and QBI Deduction for Freelancers for how a retirement contribution's size also moves your §199A deduction.

Authoritative References

• 26 U.S. Code §4972 — Tax on nondeductible employer contributions to qualified employer plans (Cornell LII)
• 26 U.S. Code §4973 — Tax on excess contributions to certain tax-favored accounts and annuities (Cornell LII)
• 26 U.S. Code §404 — Deduction for contributions of an employer to an employee's trust or annuity plan, especially subsections (a)(8) self-employed special rules and (h) SEP-specific limitations (Cornell LII)
• 26 U.S. Code §401 — Qualified pension, profit-sharing, and stock bonus plans, especially subsection (c)(2) earned income and (c)(4) employer/self-employed treatment (Cornell LII)
• 26 U.S. Code §402 — Taxability of beneficiary of employees' trust, especially subsection (h) treatment of SEP contributions and the (h)(2) excess rule (Cornell LII)
• 26 U.S. Code §408 — Individual retirement accounts, especially subsection (k) simplified employee pension defined and (d)(4) and (d)(7)(B) excess-contribution/exclusion rules (Cornell LII)
• 26 U.S. Code §219 — Retirement savings, especially subsection (b)(2) excluding employer SEP contributions from this section and (b)(5)(A) the personal-IRA deduction limit (Cornell LII)
• IRS Notice 2025-67 — 2026 cost-of-living adjusted limitations on retirement plans and IRAs (IRS)
• IRS Publication 560 — Retirement Plans for Small Business (SEP, SIMPLE, and Qualified Plans), including the Rate Table and Deduction Worksheet for Self-Employed, the "Tax treatment of excess contributions" rule, and the Excise Tax for Nondeductible (Excess) Contributions section (IRS)
• IRS Publication 590-A — Contributions to Individual Retirement Arrangements (IRAs), including the 6% Tax on Excess Contributions and the withdrawal-by-due-date correction (IRS)
• Instructions for Form 5330 — Schedule A, Tax on Nondeductible Employer Contributions to Qualified Employer Plans (Section 4972) (IRS)
• About Form 5330, Return of Excise Taxes Related to Employee Benefit Plans (IRS)
• About Form 5329, Additional Taxes on Qualified Plans (Including IRAs) and Other Tax-Favored Accounts (IRS)

The fix for this problem is almost always upstream of the SEP contribution itself: knowing your real net profit before you fund it, not after. Start a free CentSense account to keep your business income and expenses current all year, so a retirement contribution sized in December is sized off your actual numbers rather than a projection. Free tier includes 10 AI scans a month, no credit card required — or upgrade to the Solo plan for $5/month for unlimited scans, mileage tracking, and a CPA-ready CSV export. Start free →

This guide is general education for U.S. self-employed freelancers filing in 2026. It is not personalized tax advice. Whether a specific SEP-IRA or Solo 401(k) contribution exceeds your actual deduction limit, whether any portion of it can be returned under your plan's own terms, and how a carryforward or excise tax would be computed and reported on your own return are fact-specific determinations. Consult a CPA or EA before relying on any figure in this post for your own return.