Two drivers, one car: keeping separate mileage logs

Why you can't just split one total

The standard mileage deduction under IRS Publication 463 is built around a driver's own business trips — date, miles, destination, purpose — each one a real event with a real person behind the wheel. There's no IRS mechanism for "the household drove 12,000 business miles, so each spouse claims 6,000." If two people drive the same car for separate gig work, the miles belong to whoever was actually driving on that trip, and get logged and claimed separately, even if you file a joint return.

This matters most for a married couple filing jointly, where it might feel like it "comes out the same" to just add up one number. It doesn't necessarily — and more importantly, each spouse's Schedule C (self-employed people generally file their own, even on a joint 1040) needs its own substantiated log to survive a records request, not a number backed into after the fact.

What to keep separate

• The trip log itself — whichever app or notebook you use, each driver's business trips should be attributable to that driver, not merged into one feed.
• Business-use percentage — see figuring your business-use %. With two people driving the same car for both business and personal reasons, this can genuinely get complicated; each driver's percentage is their own business miles over the same car's total miles, which means the two percentages don't need to add to 100%, and won't unless every mile in the car is accounted as one or the other driver's business or personal use.
• Vehicle expenses, if using actual expenses instead of standard mileage — these need to be allocated between the two drivers' business uses in a way you can explain, not assumed to split evenly.

A practical fix: log by driver, not just by trip

If you're using an app to auto-detect trips on a shared car, the biggest practical risk isn't a missing rule — it's a mixed-up log, where the app doesn't know who was actually driving and one person's trips get attributed to the other, or duplicated across both accounts. Whatever tool you use, check that trips are tied to the person who requested and drove them, not to the vehicle alone, especially if both of you are signed in on the same device or plan at different times.

The 2026 rate applies per driver, same as any solo driver

Each driver applies the 2026 split-year rate to their own business miles: 72.5¢ per mile January 1–June 30, 76¢ from July 1 onward, from Notice 2026-10 (IR-2025-128) and Announcement 2026-11 (IRB 2026-29). There's no household-level version of the rate — it's always applied to one driver's own business miles.