Business people keep a mileage log mainly to support a mileage tax deduction from the IRS. When filing your taxes, you can receive a deduction for each mile travelled for business purposes. Each year, the IRS figures an amount per mile that people can deduct. In case you're audited, you should have a professional mileage log to prove to an IRS agent that you deducted the correct amount from your tax return.
Draw six columns and quarter-inch rows in a notebook, or open a spreadsheet with six columns on your computer. Your mileage log should look as professional as possible, so a computer spreadsheet program is recommended.
Label the columns with the following titles from left to right: "Date," "Beginning Odometer Mileage," "Ending Odometer Mileage," "Location," "Business Purpose" and "Client." This information will give a clear picture of how far you travelled, and how that trip related to your business.
Record the accurate information in each row for every business trip or activity. Write legibly in the mileage log if you use a notebook. If you're audited, an IRS agent will review your mileage log, so make sure it's correct and neatly completed.