How to calculate IFTA: a step-by-step guide
Work out quarterly IFTA fuel tax by hand: fleet MPG, taxable gallons by state, credits, surcharges, a worked example, the records to keep and the due dates.
IFTA looks complicated until you see that it is one piece of arithmetic repeated once per state. You drove some miles in each state and you bought some fuel in each state. IFTA moves the fuel tax you paid at the pump to the states where you actually burned the fuel. If you fueled in cheap-tax states and drove through expensive-tax states, you owe the difference. If it went the other way, you get a credit.
This guide walks through the math by hand so you understand what the numbers on your return mean. The free IFTA calculator does the same steps for every state at once, and the IFTA rates pages have the current diesel rate and surcharge for each quarter.
Who has to file
You need an IFTA license if you run a qualified motor vehicle in two or more member states or provinces. A qualified vehicle is one over 26,000 pounds gross vehicle weight, or with three or more axles regardless of weight, or a combination over 26,000 pounds (Washington DOL, IFTA welcome packet). You license with your base jurisdiction, the state where you are registered and keep your records, and you file one return there every quarter that covers every state.
A return is due even for a quarter with no miles. Florida’s return instructions say it plainly: the return must be filed even if you did not operate or buy fuel in any IFTA jurisdiction, by marking the “No Operations” box (FLHSMV form 85800).
Due dates
| Quarter | Months covered | Return due |
|---|---|---|
| Q1 | January – March | April 30 |
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