If you drive for work, every business mile you don't write down is money you can't claim. The fix is not complicated: a log kept the same day, with the four facts a tax authority expects to see, and receipts for the car's costs.
Work out what your miles are worth with the free Mileage Deduction Calculator.
What a mileage log needs on every line
For each business trip, record the date, the miles (start and end odometer readings are the strongest evidence), where you went and why: the client, the job or the errand. Parking and tolls for business trips are usually recorded separately. A note like "client visit, Hale Dental" is far better than "work". Write the trip down on the day; logs rebuilt months later from memory are the ones that get questioned.
Commuting usually doesn't count
In many countries the drive between home and a regular workplace is treated as personal commuting, not business mileage. Trips from your workplace to a client, between job sites, or to pick up supplies typically are business. If you work from a home office the rules can differ. Check your tax authority's guidance for your situation; this guide is general information, not tax advice.
Standard rate or actual costs?
There are two common ways to turn driving into a deduction:
- Standard mileage: business miles × the official per-mile rate, plus business parking and tolls. 8,400 miles at an example rate of $0.70 is $5,880.
- Actual costs: add up fuel, repairs, insurance, registration, depreciation or lease costs, then multiply by your business-use percentage (business miles ÷ total miles). $9,200 of costs at 62% business use is $5,704.
Which you may use, and whether you can switch between years, depends on local rules. The free Business Use Percentage Calculator shows both figures side by side.
Record the odometer twice a year
Business-use percentage needs total miles for the year, so note the odometer on 1 January and 31 December. A photo of the dashboard on those days takes five seconds and settles any doubt later.
Make it a two-minute habit
Keep the log where you'll actually use it: a spreadsheet on your phone or a paper log in the glovebox. The Mileage & Vehicle Expense Log calculates miles from odometer readings and builds the year summary for both methods; the Printable Mileage Log Book is the pen-and-paper version.
This guide is general information, not tax or legal advice. Rates in the examples are illustrative; use the current official rate for your tax year.