How the IFTA calculation works
IFTA lets a carrier file one fuel tax return with its base jurisdiction instead of one per state. Each quarter you report the miles driven and the fuel bought in every member state and Canadian province. The math is the same for everyone:
- Fleet MPG = total miles ÷ total gallons (all jurisdictions together).
- Taxable gallons in a state = miles in that state ÷ fleet MPG.
- Net taxable gallons = taxable gallons − tax-paid gallons you bought in that state.
- Tax = net taxable gallons × that state's rate. A negative number is a credit.
Kentucky and Virginia also charge a surcharge on every taxable gallon, with no credit for fuel bought there; the calculator adds it. Oregon has no IFTA diesel rate listed — heavy trucks there pay Oregon's weight-mile tax instead.
Rates and due dates
This calculator uses the diesel rates for 3Q 2026 (July 1 – September 30, 2026). Rates change every quarter, so check the IFTA tax matrix before you file. Returns are due April 30, July 31, October 31 and January 31, even for a quarter with no miles.
The result is an estimate: it treats all miles as taxable and leaves out penalties and interest. Your base jurisdiction's return is what counts. Keep your trip and fuel records — an IFTA audit asks for them.