Odometer Trip Mileage Calculator

Road44, the driving log app mentioned below, is our app. Quotes from IRS Publication 463 (2025) were checked in September 2026. This page is general information, not tax advice.

How to work out trip mileage from odometer readings

The formula is one line: end reading minus start reading is the distance for that trip. It works the same in miles or kilometers, because the odometer counts in whatever unit your dash shows.

The calculator opens with three example trips. Trip 1 runs from 24,310.2 to 24,318.9, which is 8.7 miles. Trip 2 runs from 24,318.9 to 24,342.5, or 23.6 miles. Trip 3 runs from 24,350.0 to 24,362.4, or 12.4 miles. The running total after each trip is 8.7, 32.3 and 44.7 miles, so the three trips come to 44.7 miles.

Write down the tenths digit. It's the rightmost number on most odometers, and it keeps short trips accurate. The calculator counts each reading to the tenth and adds whole tenths, so the rows always add up exactly to the total.

Readings should chain. If the car sat parked between two trips, the second one starts at the reading where the first one ended, as trips 1 and 2 do here. Trip 3 starts at 24,350.0, though, 7.5 miles past where trip 2 ended. The calculator shows that as odometer miles between trips: the car covered 7.5 miles that aren't in the log. If a trip starts below where the last one ended, the calculator adds a note to that row, since one of the readings is probably a typo.

The total also shows in the other unit. One mile is exactly 1.609344 km, according to NIST SP 811, so 44.7 miles is 71.9 km.

When the odometer rolls over

A mechanical odometer has a fixed number of wheels. Many show 5 digits before the tenths, with a top reading of 99,999.9, or 6 digits, topping out at 999,999.9. One more tenth and every wheel turns back to zero, so a trip's end reading can come out lower than its start. Federal odometer rules plan for this: the disclosure statement used when a vehicle is sold includes a statement for mileage beyond the odometer's mechanical limits (49 CFR 580.5).

The fix is to add one full cycle to the end reading before you subtract: 100,000 for a 5-digit odometer or 1,000,000 for a 6-digit one. A trip from 99,987.4 to 12.6 on a 5-digit odometer is (12.6 + 100,000) − 99,987.4 = 25.2 miles. The tenths carry over too, so 99,999.9 to 0.3 is 0.4 miles. Set the odometer size under Odometer settings and the calculator does the math and marks the row as rolled over.

Rollover only happens near the top reading. If the start isn't close to 99,999.9 and the end is lower, you're probably looking at a typo. With the 6-digit setting, a start of 99,987.4 and an end of 12.6 would count as 900,025.2 miles. The calculator adds a note to any single trip over 1,000 miles, so a mistake like that stands out.

Not every odometer rolls over. Some digital odometers stop at their top reading instead, so check your owner's manual before you set an odometer size.

What a mileage log should show

For car expenses, IRS Publication 463 asks you to record, among other things, "the mileage for each business use, and the total miles for the year" (Table 5-1). Its sample "Daily Business Mileage and Expense Log" (Table 5-2) has columns for the date, destination, business purpose, odometer start and stop readings, miles this trip and expenses, with rows for a weekly total and the total year-to-date. This calculator covers the odometer and miles columns. The rest is up to you.

Timing matters too. Pub 463 says "You should record the elements of an expense or of a business use at or near the time of the expense or use and support it with sufficient documentary evidence." It adds: "If you maintain a log on a weekly basis that accounts for use during the week, the log is considered a timely kept record."

When one car is used for business and personal trips, "You can divide your expense based on the miles driven for each purpose." Commuting counts as personal: "Transportation expenses between your home and your main or regular place of work are personal commuting expenses." The gap check is useful here. Miles driven between logged trips still count toward the year's total, even when they aren't business miles.

The IRS standard mileage rate is set per mile, and in 2026 it changed on July 1, so which rate applies depends on the date of each trip. See the IRS standard mileage rates page for the current figures. This calculator works out distance only.

Keep an odometer log in Road44

A calculator is handy for checking a week of readings. For a log you keep all year, Road44 is the driving log app we built, and it stores odometer readings with each drive:

• Each drive can hold a start and end odometer reading or a trip distance you type in, and every field is optional. Road44 works out distance as end minus start. A typed distance takes the place of the odometer pair, so for a trip where the odometer rolled over, work out the distance here and type it in.
• The start sheet for a live drive has an optional start-odometer field, so you can note the reading before you pull out.
• Miles or kilometers (and gallons or liters) are set in the menu, and the first setting follows your device's region.
• Pick Distance as your goal metric and the home screen totals, charts and calendar show distance. The all-time goal is free; weekly and monthly goals are part of Pro.
• Purpose chips on each drive cover Business, Personal, Commute and Medical. Breakdowns by purpose and your average trip distance are on the Insights screen, which is part of Pro.
• The logbook exports free as Text, CSV, PDF or PNG, with no watermark. Date, duration and distance are always included.

There's no account, and drives stay on your phone. Road44 is a personal record, not an official or certified logbook, and not tax advice. Learner drivers counting practice hours rather than miles can use the supervised driving hours calculator and our driving log template vs app guide.