What the IRS requires in a mileage log

For each business trip, the IRS wants the date, the destination, the business purpose and the miles driven, recorded at or near the time of the trip. Add your odometer readings at the start and end of the year so the total is backed up.

What to record for each trip

Date of the trip.
Destination, the place you drove to.
Business purpose: the client, the job or the reason.
Miles driven for that trip.

For the year, record total miles driven (business and personal), ideally from odometer readings on January 1 and December 31. The IRS uses the share of business miles to check your claim.

When to record it

Publication 463 asks for records made at or near the time of the trip. A log rebuilt from memory at tax time carries much less weight than one kept as you go.

Standard rate or actual expenses

If you own the car, choose the standard mileage rate in the first year you use it for business; you can switch to actual expenses later. For a leased car, if you choose the standard rate you must use it for the whole lease. Business parking and tolls are deductible on top of the standard rate.

How long to keep it

Keep the log for as long as the IRS can examine the return, normally three years from when you file.

Who needs it

Self-employed people claiming the deduction on Schedule C, and employees whose employer reimburses mileage under an accountable plan. W-2 employees can't deduct unreimbursed mileage on their federal return.