If you've ever stared at an IFTA worksheet and wondered where to begin, this guide is for you. We'll walk through the process from raw trip and fuel data to a final tax number—with examples you can follow.
Data You Need Before You Start
You can't calculate IFTA accurately without total miles driven and gallons purchased, miles by state or province, gallons by state or province, and current IFTA tax rates for the quarter. Gathering this up front makes the math much easier.
Step 1 – Calculate Total Miles and Gallons
First, total up all miles driven in the period (taxable and non-taxable) and all gallons of fuel purchased in all jurisdictions. This gives you your fleet's overall MPG, which is crucial for checking your work later.
Step 2 – Break Down Miles and Gallons by Jurisdiction
Next, allocate those totals across each jurisdiction where your vehicles operated. You can use trip sheets or driver logs, GPS/ELD jurisdiction reports, or TMS distance reports. Be meticulous—this breakdown drives everything that follows.
Step 3 – Apply Current IFTA Tax Rates
Using the quarter's official rate table, calculate for each jurisdiction:
- Taxable gallons = Miles in jurisdiction ÷ Fleet MPG
- Tax due = Taxable gallons × jurisdiction's tax rate
This step turns your distance into a tax liability by jurisdiction.
Step 4 – Calculate Net Tax Due or Credit
For each jurisdiction, compare tax due to tax paid at the pump (via fuel receipts and invoices). If tax due is greater than tax paid, you owe the difference. If tax paid is greater than tax due, you have a credit. Add up all jurisdictions to find your overall net tax due or refund under IFTA.
Checking Your Work (Avoiding Common Errors)
Before you file, sanity-check: Does total distance match odometer or GPS reports? Is your overall MPG within a realistic range for your equipment and routes? Do your jurisdiction totals match your fuel receipts and trip records? Using the iFuelTax Mileage & Tax Calculator can help catch mistakes early.
Automating the Process With iFuelTax
If doing this by hand every quarter feels like too much, iFuelTax can automate the import and mapping of your mileage and fuel data, application of current tax rates, and generation of file-ready reports and audit packs. You stay in control of the numbers—without living in spreadsheets.