Solo 401(k) vs. SIMPLE IRA: What Happens to Your Retirement Plan the Moment You Hire Your First Employee

Published: September 15, 2026 · Reading time: 11 min

TL;DR: A solo 401(k) legally requires that you have no eligible common-law employees. The moment a new hire crosses IRC §410(a)(1)'s one-year/1,000-hour threshold (or the 2-year/500-hour long-term part-time rule under §401(k)(15)), your plan document requires you to either open it up or shut it down. The common downgrade — a SIMPLE IRA — caps your own 2026 deferral at a flat $17,000 plus a 3%-of-comp match, a fraction of the solo 401(k)'s $72,000 combined ceiling. A SIMPLE 401(k) doesn't fix this: it shares the SIMPLE's low dollar limits under §401(k)(11), forbids running alongside any other plan, and adds a full 401(k)'s Form 5500 paperwork for no extra room. The option most freelancers never hear about — amending into a safe-harbor 401(k) under §401(k)(13) — can preserve the full $72,000 ceiling, at the price of real ongoing administration. In the worked example below, the wrong choice costs a $260,000-profit freelancer about $47,647.62 of retirement shelter in a single year.

Hiring your first employee is supposed to feel like a milestone. For your retirement plan, it's a legal trigger — and most freelancers don't find out how big the numbers involved are until an accountant or a plan provider tells them, usually after the hire is already made.

Why a Solo 401(k) Can't Just "Add" an Employee

A solo 401(k) — also called a one-participant 401(k) — isn't a special plan type in the statute. It's an ordinary 401(k) that happens to have zero eligible participants other than the business owner (and a spouse who works in the business). The simplified administration solo 401(k) providers advertise — no Form 5500-EZ below $250,000 in assets, no nondiscrimination testing — exists because there's nobody else in the plan to test against or report on.

That status ends the moment a common-law employee becomes eligible to participate. Under IRC §410(a)(1)(A), a qualified plan generally cannot require an employee to complete a period of service extending beyond the later of the date they turn 21 or the date they complete a "year of service" — defined at §410(a)(3)(A) as a 12-month period with at least 1,000 hours worked. A plan is free to exclude an employee before that point; it cannot exclude them after it.

There's a second, newer trigger for part-timers who never hit 1,000 hours in a year. SECURE 2.0 added the long-term part-time worker rule, now at §401(k)(15) (cross-referencing the eligibility provision at §401(k)(2)(D)(ii)): an employee who completes 2 consecutive 12-month periods with at least 500 hours of service in each must be let into the plan's deferral feature, even if they never cross the traditional 1,000-hour line.

node -e "
const scenarios = [
  { desc: 'Full-time hire, 1,600 hrs/yr', hoursYr1: 1600 },
  { desc: 'Part-time hire, 700 hrs/yr', hoursYr1: 700 },
];
for (const s of scenarios) {
  const hitsFullTimeRule = s.hoursYr1 >= 1000;
  console.log(s.desc + ':', hitsFullTimeRule
    ? 'eligible after 1 year of service (Sec. 410(a)(1))'
    : 'not yet eligible under the 1,000-hour rule; eligible after 2 consecutive years at 500+ hrs (Sec. 401(k)(15))');
}
"

Full-time hire, 1,600 hrs/yr: eligible after 1 year of service (Sec. 410(a)(1))
Part-time hire, 700 hrs/yr: not yet eligible under the 1,000-hour rule; eligible after 2 consecutive years at 500+ hrs (Sec. 401(k)(15))

So a full-time hire forces the question inside a year. A genuinely part-time hire buys you more runway — but not forever.

The Two Real Paths Forward

Once your plan document requires you to open the door, you have two structurally different options — not one obvious answer.

The SIMPLE 401(k) — a third, less obvious option — sits in an unusual spot: it shares the SIMPLE IRA's low dollar ceiling but the safe-harbor 401(k)'s administrative burden. More on why that combination rarely makes sense below.

The 2026 Numbers, Verified

Every figure above is from the IRS's own 2026 cost-of-living adjustment table (Notice 2025-67) and the underlying Internal Revenue Code sections, fetched and read directly for this article rather than carried over from an earlier year. This matters here specifically: grep -rl 'combined.*\$70,000\|\$70,000.*combined\|the 2026.*\$70,000\|\$70,000 (' src/content/blog --include=*.mdx | xargs grep -l '\$23,500' | wc -l finds 5 existing retirement-plan posts on this site (backdoor-roth-ira-freelancers, defined-benefit-plan-high-earning-freelancers, mega-backdoor-roth-solo-401k-freelancers, solo-401k-contribution-limits-freelancers, traditional-vs-roth-ira-freelancers) that still show the solo 401(k)'s 2026 combined ceiling as $70,000 and the employee deferral as $23,500 — those are the correct 2025 figures, not 2026's. (A sixth, self-employment-tax-explained.mdx, shows an even staler $69,000 combined cap.) The 2026 numbers are $72,000 and $24,500, confirmed directly against the IRS COLA table reproduced above. A corpus-wide sweep to fix these is a separate follow-up, out of scope here.

Worked Example: What the Downgrade Actually Costs

Dana is a freelance software developer — Schedule C sole proprietor, single, age 45, no other income. Software development isn't on the Specified Service Trade or Business list under §199A, so there's no SSTB phase-out to worry about at any income level here — but §199A has a separate W-2-wage/2.5%-of-property limitation that phases in above a taxable-income threshold ($201,750 single for 2026, per Rev. Proc. 2025-32) regardless of SSTB status, checked explicitly below once Year 2's taxable income crosses that line.

Year 1: Solo, at the ceiling

Dana nets $260,000 on Schedule C and runs her solo 401(k) at the max.

node -e "
const netProfit = 260000;
const netSE = netProfit * 0.9235;
const wageBase2026 = 184500;
const seTax = netSE > wageBase2026
  ? (wageBase2026 * 0.124 + netSE * 0.029)
  : (netSE * 0.153);
const halfSE = seTax / 2;
const adjustedBase = netProfit - halfSE;
const employerRate = 0.25 / 1.25; // 25% of comp after the contribution === 20% of comp before it
const employerContribution = adjustedBase * employerRate;
const employeeDeferral = 24500;
const combinedRaw = employeeDeferral + employerContribution;
const dcLimit2026 = 72000;
console.log('net SE earnings (92.35% of profit)', netSE.toFixed(2));
console.log('2026 SE tax', seTax.toFixed(2));
console.log('deductible half', halfSE.toFixed(2));
console.log('adjusted earnings base', adjustedBase.toFixed(2));
console.log('employer profit-sharing (20% of base)', employerContribution.toFixed(2));
console.log('employee deferral', employeeDeferral.toFixed(2));
console.log('combined, uncapped', combinedRaw.toFixed(2));
console.log('combined, capped at the 2026 Sec. 415(c) limit', Math.min(combinedRaw, dcLimit2026).toFixed(2));
"

net SE earnings (92.35% of profit) 240110.00
2026 SE tax 29841.19
deductible half 14920.60
adjusted earnings base 245079.40
employer profit-sharing (20% of base) 49015.88
employee deferral 24500.00
combined, uncapped 73515.88
combined, capped at the 2026 Sec. 415(c) limit 72000.00

Her raw entitlement ($73,515.88) already exceeds the cap, so the $72,000 §415(c) ceiling binds — she's genuinely maxed out.

Year 2: She hires Jordan, downgrades to a SIMPLE IRA

Dana hires Jordan at $32,000/year. Once Jordan crosses the one-year/1,000-hour eligibility line, Dana terminates the solo 401(k) and opens a SIMPLE IRA for both of them, choosing the standard 3%-match design. Her Schedule C profit — after Jordan's wages, payroll taxes, and the SIMPLE match are already deducted as business expenses — stays at $260,000, so the comparison isolates the retirement-plan effect alone.

node -e "
const netProfit = 260000;
const netSE = netProfit * 0.9235;
const wageBase2026 = 184500;
const seTax = wageBase2026 * 0.124 + netSE * 0.029; // netSE exceeds the wage base
const halfSE = seTax / 2;
const adjustedBase = netProfit - halfSE; // same net-earnings base as the solo 401(k) calc above

const ownDeferral = 17000; // 2026 SIMPLE deferral ceiling
const ownMatch = adjustedBase * 0.03; // 3% mandatory match, on the same adjusted-earnings base
const ownTotal = ownDeferral + ownMatch;

const jordanSalary = 32000;
const jordanMatch = jordanSalary * 0.03; // no comp cap and no circularity on a common-law employee's match

console.log('own elective deferral', ownDeferral.toFixed(2));
console.log('own 3% match (approx., same base as the solo 401(k) calc)', ownMatch.toFixed(2));
console.log('own total SIMPLE shelter', ownTotal.toFixed(2));
console.log('Jordan mandatory 3% match (business expense)', jordanMatch.toFixed(2));
console.log('drop vs. the Year 1 solo 401(k) ceiling', (72000 - ownTotal).toFixed(2));
"

own elective deferral 17000.00
own 3% match (approx., same base as the solo 401(k) calc) 7352.38
own total SIMPLE shelter 24352.38
Jordan mandatory 3% match (business expense) 960.00
drop vs. the Year 1 solo 401(k) ceiling 47647.62

Her own SIMPLE match figure is computed here on the same net-self-employment-earnings base as the solo 401(k) calculation for consistency; a plan provider's IRS Publication 560 worksheet may adjust it by a small further amount, the same caveat that applies to any self-employed retirement-contribution estimate. It doesn't move the conclusion: Dana's own retirement shelter drops from $72,000 to about $24,352 — a $47,647.62 reduction — the year she hires her first employee, if she takes the SIMPLE IRA path.

What that's worth in real tax dollars

Both years land inside the same 2026 single-filer 24% bracket ($105,700–$201,775 per Rev. Proc. 2025-32), so the comparison doesn't straddle brackets:

node -e "
function taxableIncome(netProfit, retirementDeduction) {
  const netSE = netProfit * 0.9235;
  const wageBase2026 = 184500;
  const seTax = netSE > wageBase2026 ? (wageBase2026*0.124 + netSE*0.029) : (netSE*0.153);
  const halfSE = seTax / 2;
  const AGI = netProfit - halfSE - retirementDeduction;
  const stdDeduction = 16100; // 2026 single filer, per Rev. Proc. 2025-32 (IRB 2025-45)
  const taxableIncomeBeforeQBI = AGI - stdDeduction;
  const qbi20 = AGI * 0.20;
  const cap20 = taxableIncomeBeforeQBI * 0.20; // Sec. 199A(e)(1) cap, computed before the QBI deduction itself
  const qbiDeduction = Math.min(qbi20, cap20);
  return taxableIncomeBeforeQBI - qbiDeduction;
}
const t1 = taxableIncome(260000, 72000);      // Year 1, solo 401(k)
const t2 = taxableIncome(260000, 24352.38);   // Year 2, SIMPLE IRA
const taxableIncomeDelta = t2 - t1; // the shelter gap doesn't translate 1:1 -- see below
console.log('Year 1 taxable income', t1.toFixed(2), '-> in 24% bracket?', t1 > 105700 && t1 <= 201775);
console.log('Year 2 taxable income', t2.toFixed(2), '-> in 24% bracket?', t2 > 105700 && t2 <= 201775);
console.log('actual taxable-income delta (t2 - t1)', taxableIncomeDelta.toFixed(2));
console.log('value of that delta at 24%', (taxableIncomeDelta * 0.24).toFixed(2));
"

Year 1 taxable income 125583.52 -> in 24% bracket? true
Year 2 taxable income 163701.62 -> in 24% bracket? true
actual taxable-income delta (t2 - t1) 38118.10
value of that delta at 24% 9148.34

The $47,647.62 shelter gap doesn't translate dollar-for-dollar into a bigger tax bill: the self-employed retirement deduction reduces the QBI base, so each dollar of shelter that disappears also shrinks the QBI deduction by 20 cents — the same §199A clawback the QBI guide and this batch's own SALT cap post work through. Only 80 cents of the gap ($38,118.10) actually shows up as taxable income, which is exactly why the taxable-income delta above is 80% of $47,647.62. That's $9,148.34 of current-year federal tax exposure created by the plan downgrade — money that isn't lost forever (it would have been tax-deferred either way, not tax-free), but that shows up as real, immediate cash flow out the door the year Dana hires.

Year 2's taxable income before the QBI deduction ($204,627.02) crosses the 2026 single-filer §199A threshold of $201,750 — so unlike Year 1, the separate W-2-wage/2.5%-of-property limitation actually phases in that year, and checking "not an SSTB" alone isn't enough to clear it:

node -e "
const taxableIncomeBeforeQBI = 204627.02;
const AGI = 220727.025;
const qbi20 = AGI * 0.20;
const threshold = 201750, phaseInRange = 75000; // 2026 single, OBBBA-widened range
const jordanWages = 32000;
const wageLimit = jordanWages * 0.50; // Dana has no other W-2 employees or qualified property (UBIA ~0)
const ratio = Math.min(Math.max((taxableIncomeBeforeQBI - threshold) / phaseInRange, 0), 1);
const perBusinessLimit = qbi20 - (qbi20 - wageLimit) * ratio;
const overallCap = taxableIncomeBeforeQBI * 0.20;
console.log('phase-in ratio', ratio.toFixed(6));
console.log('20% of QBI (uncapped)', qbi20.toFixed(2));
console.log('W-2-wage-based per-business limit after phase-in', perBusinessLimit.toFixed(2));
console.log('overall 20%-of-taxable-income cap', overallCap.toFixed(2));
console.log('binding limit', Math.min(qbi20, perBusinessLimit, overallCap).toFixed(2));
"

phase-in ratio 0.038360
20% of QBI (uncapped) 44145.40
W-2-wage-based per-business limit after phase-in 43065.74
overall 20%-of-taxable-income cap 40925.40
binding limit 40925.40

The wage-based limit (checked here because Dana now has a W-2 employee) only shaves the ceiling to $43,065.74 — still above the overall taxable-income cap of $40,925.40, which is what actually binds and is why the $163,701.62 figure above holds. In both years the §199A(e)(1) taxable-income cap — not the naive 20%-of-QBI figure, and not the wage limit either — is what actually limits her QBI deduction; the same pattern this corpus's QBI guide warns readers to check for every year regardless of income level, and Year 2 is a reminder that "not an SSTB" only clears one of §199A's separate tests.

The alternative Dana never got a quote for

If Dana instead amends her solo 401(k) into a safe-harbor 401(k) — using a §401(k)(13) automatic-contribution design or a traditional matching/nonelective safe-harbor formula — the math looks like Year 1 again: her own ceiling stays at $72,000. What Jordan costs depends on the design: a safe-harbor match (commonly 3% of comp, $960 here) only exempts elective deferrals from ADP/ACP testing — the large employer profit-sharing allocation that gets Dana to $72,000 is a separate contribution that still has to satisfy §401(a)(4) nondiscrimination on its own, typically a cross-tested formula with a "gateway" minimum for Jordan (commonly around 5% of compensation, roughly $1,600) layered on top of the $960 match, for about $2,560 total. A safe-harbor nonelective design (commonly 3% of comp for every eligible employee, also $960 here) can instead count toward that same 5% gateway, so Jordan's total can land closer to the $1,600 gateway figure alone rather than stacking both. Either way, get an actual quote from a TPA — the two designs aren't interchangeable on cost. The ongoing TPA/plan-document/Form 5500-SF administration a SIMPLE IRA doesn't require at all typically runs a few hundred to a couple thousand dollars a year for a plan this size, on top of whichever of those figures applies to Jordan. At Dana's roughly $9,150-a-year tax-deferral value, that overhead often still pencils out — but almost nobody presents it as an option next to "just open a SIMPLE," so most freelancers never see the comparison, or the real cost of it.

Why the SIMPLE 401(k) Is Rarely the Right Answer

A SIMPLE 401(k), created under IRC §401(k)(11), is a genuine 401(k)-type cash-or-deferred arrangement — not a SIMPLE IRA with a different name. It inherits the SIMPLE's contribution structure by cross-reference to §408(p): the same $17,000 deferral, the same 3%-match-or-2%-nonelective employer formula. What it doesn't inherit is the SIMPLE IRA's light administration. Because it's a §401(a)-qualified plan, it needs a plan document and — absent the one-participant exemption, which doesn't apply once there's a non-owner employee — an annual Form 5500 filing, the same overhead as a full 401(k).

On top of that, §401(k)(11)(C) imposes an exclusive-plan requirement: no contributions or benefits can accrue under any other qualified plan of the employer, for any eligible employee, in a year the SIMPLE 401(k) is used. You can't run it alongside a separate profit-sharing plan the way you sometimes can with other structures.

The one real advantage a SIMPLE 401(k) has over a SIMPLE IRA is narrow but genuine: a SIMPLE IRA is an IRA-based account, and under §72(t)(6), an early distribution taken within the first 2 years of participating in a SIMPLE carries a 25% additional tax instead of the usual 10%. A SIMPLE 401(k) balance, as a qualified-plan account rather than an IRA, isn't subject to that enhanced 25% penalty, and a 401(k)-type plan can be designed to permit participant loans, which a SIMPLE IRA — again, because it's an IRA — cannot offer at all. Outside of wanting loan access or specifically avoiding the SIMPLE IRA's 2-year penalty window, the SIMPLE 401(k)'s extra paperwork buys nothing a SIMPLE IRA doesn't already deliver.

SIMPLE Eligibility Is Faster Than 401(k) Eligibility

One more asymmetry worth knowing before you pick a plan: once you've adopted a SIMPLE (either flavor), you can't hold new hires out of it the way a 401(k) can. Under §408(p)(4)(A), any employee who received at least $5,000 in compensation from you in any 2 preceding years, and is reasonably expected to earn at least $5,000 this year, must be allowed to participate — no age-21 requirement, no 1,000-hour year-of-service test. A 401(k), by contrast, can lawfully exclude an employee until they clear the higher §410(a)(1) bar (or the LTPT rule). For a freelancer who expects to keep hiring, that means a SIMPLE reaches new employees — and triggers their mandatory match cost — noticeably sooner than a standard 401(k) would.

Common Mistakes to Avoid

• Assuming the solo 401(k) has to close the instant you sign an offer letter. It doesn't — a new hire generally isn't plan-eligible until they clear a year of service (or the 2-year/500-hour LTPT rule), which can buy real time to plan the transition rather than scrambling.
• Defaulting to a SIMPLE IRA without pricing the safe-harbor 401(k) alternative. The SIMPLE is simpler to administer, but at higher profit levels the tax value of the higher ceiling routinely exceeds the extra administrative cost — a comparison most freelancers never actually run.
• Choosing a SIMPLE 401(k) thinking it's a bigger version of a SIMPLE IRA. It shares the exact same low dollar limits; the only real differences are added paperwork and, narrowly, loan availability and the absence of the SIMPLE IRA's 25% early-withdrawal penalty.
• Rolling an old solo 401(k) balance straight into a brand-new SIMPLE IRA. That rollover is restricted during the SIMPLE's first 2 years under §408(p)(1)(B), which borrows §72(t)(6)'s 2-year period; roll to a traditional IRA instead if the SIMPLE isn't yet 2 years old.
• Forgetting that the employer contribution is mandatory once a SIMPLE is adopted. Unlike a SEP, you can't skip the match or nonelective contribution in a lean year without formally terminating the plan.
• Not checking whether the new hire is even a common-law employee. A genuine independent contractor doesn't trigger any of this — see 1099 vs. W-2 worker classification before assuming plan eligibility applies at all.

Frequently Asked Questions

What actually happens to my solo 401(k) when I hire my first employee?

Nothing happens automatically on day one — a solo 401(k) plan document can lawfully exclude any employee until they complete a "year of service" (age 21 and 1,000 hours in a 12-month period, under §410(a)(1)(A) and §410(a)(3)(A)). But once that employee crosses that threshold, or completes 2 consecutive 12-month periods with at least 500 hours each under the long-term part-time rule (§401(k)(15)), your plan document requires you to let them in. At that point you either amend into a standard (often safe-harbor) 401(k) that covers them, or terminate it and roll your balance elsewhere.

Isn't a SIMPLE 401(k) just a solo 401(k) that allows employees?

No. A SIMPLE 401(k) under §401(k)(11) shares the SIMPLE IRA's dollar limits — a $17,000 elective deferral for 2026 plus a mandatory 3% match or 2% nonelective — nowhere near the solo 401(k)'s $72,000 combined ceiling. It also carries the exclusive-plan requirement under §401(k)(11)(C) and, as a true 401(k)-type plan, needs a plan document and Form 5500 filing. It combines a SIMPLE's low ceiling with a full 401(k)'s paperwork.

How much less can I contribute for myself if I switch from a solo 401(k) to a SIMPLE IRA?

It depends on profit, but the gap is large at higher income because the two plans scale differently. In this article's worked example, a freelancer netting $260,000 drops from a $72,000 solo 401(k) ceiling to about $24,352 of her own money in a SIMPLE IRA — a roughly $47,648 reduction. Because the retirement deduction also feeds the QBI base, only about 80% of that gap actually shows up as taxable income, worth about $9,148 in current-year federal tax exposure at her 24% marginal bracket. The gap narrows (and can even favor the SIMPLE) at lower profit levels, since the SIMPLE deferral is a flat dollar amount not tied to profit the way the solo 401(k)'s employer piece is.

Can I keep my solo 401(k)'s full contribution ceiling after hiring an employee?

Yes, by amending it into a standard 401(k) with a safe-harbor design — commonly a §401(k)(13) automatic-contribution arrangement — instead of terminating it. That preserves the full $72,000 combined 2026 ceiling but adds ongoing administration (plan document, TPA, Form 5500-SF) that a SIMPLE IRA doesn't require.

Do I have to cover a part-time employee under my retirement plan right away?

For a 401(k), generally no — a plan can wait until the employee clears the age-21/1,000-hour rule (§410(a)(1)), or 2 consecutive years at 500+ hours for someone who never hits 1,000 (§401(k)(15)). A SIMPLE plan is far less forgiving: under §408(p)(4)(A), anyone who earned at least $5,000 from you in any 2 prior years and is expected to earn $5,000 this year must be let in, a much lower bar that reaches part-timers sooner.

What happens to the money already sitting in my solo 401(k) — do I have to cash it out?

No, and doing so would trigger ordinary income tax plus likely a 10% early-withdrawal penalty. If you amend into a standard or safe-harbor 401(k), your existing balance stays invested under the amended plan. If you terminate it for a SIMPLE, the balance should roll to a traditional IRA rather than directly into the new SIMPLE IRA, since a rollover into a SIMPLE IRA from a non-SIMPLE plan is restricted during the SIMPLE's first 2 years under §408(p)(1)(B).

Authoritative References

• IRC §401(k) — Cash or deferred arrangements (including §401(k)(11) SIMPLE 401(k), §401(k)(13) automatic-contribution safe harbor, §401(k)(15) long-term part-time workers)
• IRC §408(p) — SIMPLE retirement accounts
• IRC §410(a) — Minimum age and service participation requirements
• IRC §415(c) — Limitation for defined contribution plans
• IRC §72(t) — 10% (and, for SIMPLE accounts, 25%) additional tax on early distributions
• IRS — 401(k) limit increases to $24,500 for 2026, IRA limit increases to $7,500
• IRS — COLA increases for dollar limitations on benefits and contributions

Related reading: Solo 401(k) contribution limits · SIMPLE IRA vs. SEP IRA · SEP IRA vs. Solo 401(k) · Hiring a W-2 employee vs. a 1099 contractor · Defined benefit plans for high-earning freelancers · QBI deduction for freelancers

Get the Clean Numbers Before You Call a TPA

Whichever path you take, the conversation with a plan provider or actuary starts with an accurate net profit figure — and if your Schedule C books are behind, that first quote will be a guess. CentSense scans every receipt with AI the moment it arrives, tracks mileage automatically, and exports a CPA-ready CSV so the numbers you bring to that call are numbers you can trust. Free tier includes 10 AI receipt scans a month, no credit card required; the Solo plan ($5/month) adds unlimited scans, mileage tracking, and the export.

Start free →

This article is educational and not tax or financial advice. Consult a qualified tax professional or retirement-plan actuary about your specific situation.