Starting Business Driving Mid-Year: Your First Mileage Log, the Pub 463 Months Formula, and the First-Year Method Choice (2026)

Published: October 5, 2026 · Reading time: 11 min

TL;DR: If your car was personal until you started freelancing in, say, May, you do not need mileage records for the months before. You need a good log from day one of business use, a dated odometer reading, and a method choice made in the first year. Publication 463 says: "If you want to use the standard mileage rate for a car you own, you must choose to use it in the first year the car is available for use in your business." Under actual expenses, business use is business miles divided by total miles driven that year; if you lack records for the months before the change, Publication 463's published formula for a car converted mid-year is business miles divided by total miles for the period after the change, times months of business use over 12. In 2026 every logged mile is valued by its date: 72.5 cents through June 30, 76 cents from July 1.

Most mileage advice assumes you are a calendar-year driver: odometer photo on January 1, log all year, photo on December 31. Real freelancers do not start that way. You land your first client in spring, or you buy a car in August, and the question becomes what the IRS expects for the part of the year before the business existed.

The honest answer is "less than you fear," with a few rules you cannot skip. This guide covers the ones that matter in the first year: when your clock starts, the odometer baseline, the one-time method choice, the months formula for business use, and a worked example at the split 2026 rates.

It is deliberately about the first-year mechanics. For the full-year habit, see odometer readings and your mileage log. For choosing between methods once you are past year one, see standard mileage vs actual expenses.

When does your clock start?

Your first-year clock starts on the day the car becomes available for use in your business, not on the day you bought it.

Publication 463 says that for figuring depreciation, "if you first start using the car only for personal use and later convert it to business use, you place the car in service on the date of conversion." Schedule C Part IV asks the same thing in plain form: "When did you place your vehicle in service for business purposes?" with a month, day and year.

Three cases come up:

Write the date down the day it happens. It is a thirty-second note that saves an argument later. The Schedule C Part IV guide covers how that date appears on the form, and converting personal property to business use covers the basis side if you plan to depreciate.

What records you need, and from when

You need the full set of records for business use, from the first business trip. You do not need to invent a log for months when the car was purely personal.

For a car, which is listed property, Treas. Reg. 1.274-5T(b)(6) names the elements to prove: the amount of each business use "based on the appropriate measure" (mileage for automobiles), "the total use of the listed property for the taxable period," plus the date and the business purpose. In practice that is the familiar four-part trip record: date, miles, destination, business purpose.

On timing, the same regulation, 1.274-5T(c)(1), says: "A contemporaneous log is not required, but a record of the elements of an expenditure or of a business use of listed property made at or near the time of the expenditure or use, supported by sufficient documentary evidence, has a high degree of credibility not present with respect to a statement prepared subsequent thereto when generally there is a lack of accurate recall."

Publication 463 adds that you do not need to write each trip down that day: "If you maintain a log on a weekly basis that accounts for use during the week, the log is considered a timely kept record."

So the first-year rule of thumb is simple. Start the log on the first business trip, and keep it at least weekly. The contemporaneous log requirements guide covers what a defensible entry looks like.

The odometer baseline

Per-trip odometer readings are optional. A baseline is not, practically speaking, because Schedule C Part IV asks for the year's totals: miles for business, commuting and other, out of all the miles you drove during the year.

Capture these in the first week of business use:

1. A dated photo of the odometer on the first day of business use.
2. A January 1 anchor, if you can find one. A dated oil-change, inspection or repair invoice from near the start of the year usually prints the reading. The reconstruction guide explains how to bracket a date between two invoices.
3. Purchase paperwork, if you bought the car this year, which typically records the mileage at purchase.

With a start-of-year reading and a year-end reading you can report the total honestly, and the miles before business use began simply fall into "other."

The one-time choice: standard mileage or actual expenses

The first year is when the method choice is made. Publication 463 states it directly:

"If you want to use the standard mileage rate for a car you own, you must choose to use it in the first year the car is available for use in your business. Then, in later years, you can choose to use either the standard mileage rate or actual expenses."

It continues: "You must make the choice to use the standard mileage rate by the due date (including extensions) of your return. You can't revoke the choice. However, in later years, you can switch from the standard mileage rate to the actual expenses method."

For a leased car, "you must use it for the entire lease period."

Two consequences for a mid-year starter:

• Starting on the standard rate keeps both doors open. You can switch to actual expenses later (with straight-line depreciation over the remaining life, as the switching guide explains).
• Starting on actual expenses with accelerated depreciation closes the standard-rate door for that car. Rev. Proc. 2019-46 section 4.05(3) says a taxpayer may not use the business standard mileage rate for an automobile for which the taxpayer has claimed a Section 179 deduction, claimed additional first-year depreciation such as under Section 168(k), or used MACRS. See the listed property rules and luxury auto depreciation limits before you go that route.
• Using the actual expense method in the first year at all closes the standard-rate door for that car. Under Publication 463's first-year rule quoted above, the standard mileage rate must be chosen in the first year the car is available for use in your business, so a first year on actual expenses, even without accelerated depreciation, forecloses it.

Rev. Proc. 2019-46 section 4.02 also explains what you give up by taking the standard rate: it is computed "in lieu of computing the fixed and variable costs of the automobile," and items such as "depreciation or lease payments; maintenance and repairs; tires; gasoline, including all taxes thereon; oil; insurance; and license and registration fees are included in fixed and variable costs for this purpose." Parking fees and tolls for business are separate items under section 4.03.

The months formula for business use

Under actual expenses you need a business-use percentage. If the car was 100% personal until you started, you will not have a business-use history for the early months, and Publication 463 deals with that directly. The general rule is business miles divided by total miles driven during the year, which works if you have records for the whole year; the months formula below is for a driver who lacks records for the time before the change.

It says: "If you change the use of a car from 100% personal use to business use during the tax year, you may not have mileage records for the time before the change to business use. In this case, you figure the percentage of business use for the year as follows." The steps: divide business miles by total miles driven during the period after the change, then multiply by "the number of months the car is used for business" over 12.

Its example: personal only for six months, then 15,000 miles in the last six months of which 12,000 are business. That is 80% for the period, and 80% times 6 over 12 gives a 40% business use for the year.

A caution on scope. Publication 463 states this formula in its depreciation chapter, under use for more than one purpose. Its actual-expense section separately says you "can divide your expense based on the miles driven for each purpose." Many preparers carry the formula's percentage across to the other actual costs of a converted car, but that is an application, not something the publication spells out, so confirm your preparer's approach before you rely on it.

Worked example: Theo starts client work in May 2026

Theo is a freelance home-staging consultant. He has owned his hatchback for years and used it only for personal driving. His first client site visit is May 4, 2026, and he starts logging that day.

Odometer facts:

Business miles from his log (logged by date):

Under the standard mileage rate, that is his deduction: $3,072.60, on Schedule C line 9. No percentage is involved. The rates are the IRS's: 72.5 cents (IR-2025-128) through June 30 and 76 cents (IR-2026-29) from July 1, as listed on the IRS standard mileage rates page.

Part IV totals (assuming Theo has no commuting miles because he works from home and drives to client sites):

• Total miles for the year: 54,950 minus 41,980 is 12,970
• Business miles: 4,100
• Commuting miles: 0 (assumption)
• Other miles: 12,970 minus 4,100 is 8,870, which includes the 6,230 personal miles before May 4

Now the actual-expense comparison. Theo has full-year records, including the dated January 1 reading, so the general rule applies: business miles divided by total miles driven during the year.

• Business use for the year: 4,100 divided by 12,970 is 31.61%

Suppose Theo's operating costs for the whole year were these assumptions, not real data: fuel $2,400, insurance $1,560, maintenance and tires $900, registration $180. That is $5,040. At 31.61%, the deductible share is $1,593.22, before any depreciation. (Percentages are rounded to two places; dollar figures are computed from the unrounded ratio.)

If Theo lacked records for the months before May 4, Publication 463's months formula would be the fallback:

• Total miles after the change: 54,950 minus 48,210 is 6,740
• Business use for that period: 4,100 divided by 6,740 is 60.83%
• Months of business use: May through December is 8
• Business use for the year: 60.83% times 8 over 12 is 40.55%, which on the same $5,040 gives $2,043.92 (computed from the unrounded ratio; the rounded 40.55% alone gives $2,043.72)

For an older car with low value, little depreciation is available, so Theo's cleanest first-year choice is the standard rate, which also keeps the option to switch later. A newer or more expensive car, or a different mix of costs, could change the comparison. The break-even guide shows how to run it with your own numbers.

Whether this reduces Theo's tax depends on his whole return, so this example stops at the deduction.

Common mistakes

1. Waiting until January to start the log. The clock starts on the first business trip. Every week without a log is a week you may have to reconstruct.
2. Treating the purchase date as the start date. For a car you already owned, the relevant date is when business use began.
3. Skipping the odometer baseline. Without a reading near the start of business use, your total and "other" miles become a guess.
4. Using one 2026 rate for the whole year. Miles are valued by date: 72.5 cents through June 30, 76 cents from July 1. A single-rate total is wrong whenever your trips straddle July 1.
5. Claiming MACRS or Section 179 before comparing methods. Once claimed on a car, the standard rate is closed for it.
6. Applying the months fraction to the standard rate. The 6 over 12 style formula is a business-use percentage tool. The standard rate multiplies logged business miles and nothing else.
7. Entering commuting miles for the whole year. Schedule C instructions say to enter commuting miles only for the period you drove the vehicle for business.
8. Padding the early weeks. A reconstruction must be supportable by calendars, invoices and emails. Invented trips are far worse than a thin first month.
9. Forgetting that the choice is due with the return. Publication 463 says the choice is made by the due date, including extensions, and cannot be revoked.
10. Not keeping the proof. Keep the log, odometer photos and service invoices for as long as the IRS expects.

How CentSense Helps

CentSense makes the first month of business driving easier to document:

• Log business miles by date, with destination and purpose, so every trip carries the date that decides its 2026 rate
• Scan service invoices, repair receipts and registration paperwork with AI so the dated odometer readings that anchor your year-start total are saved with your records
• Categorize vehicle receipts to the right Schedule C lines when you use the actual-expense method
• Keep business-mile totals by date and category, and pair them with your odometer photos for Part IV's total and other miles
• Export everything as CSV for your preparer

CentSense does not apply the July 1 split to a trip automatically. Log by date, and value each trip at the rate for its date when you total the year.

See also: Schedule C Line 9: Car and Truck Expenses, business-use percentage for vehicles, commuting vs business miles, and the 2026 mileage rate.

Authoritative References

• IRS Publication 463, Travel, Gift, and Car Expenses (2025 edition, the version verified for this guide)
• Rev. Proc. 2019-46, Business standard mileage rate rules (sections 4.02, 4.03, 4.05)
• IRS, Standard mileage rates (2026: 72.5 cents January 1 to June 30 per IR-2025-128; 76 cents July 1 to December 31 per IR-2026-29)
• IRS, IR-2025-128: 2026 business standard mileage rate at 72.5 cents per mile
• IRS, Instructions for Schedule C (Form 1040), Part IV, Information on Your Vehicle (2025 edition)
• IRS, Schedule C (Form 1040), Part IV, lines 43 to 47
• 26 CFR 1.274-5T, Substantiation requirements, paragraphs (b)(6) and (c)(1) (Cornell LII)

Start the log on your first client drive, not in January. Start a free CentSense account, log business miles by date, scan every service invoice and receipt the day you get it, and export a preparer-ready summary at filing time. The free tier includes 10 AI receipt scans a month, no credit card required, and the Solo plan is $5 a month when you need more.

This guide is general education for U.S. self-employed taxpayers filing Schedule C for tax year 2026. It is not personalized tax advice. The worked example uses assumed operating costs and a single set of facts; your method choice, business-use percentage and depreciation depend on your vehicle, your records and your whole return, and are best confirmed with a CPA or EA.