IFTA Calculator

How the IFTA calculation works

1. Fleet MPG = total miles in all jurisdictions ÷ total gallons put in the tanks, rounded to two decimals.
2. Taxable gallons in a jurisdiction = miles driven there ÷ fleet MPG, rounded to the nearest whole gallon.
3. Net taxable gallons = taxable gallons − tax-paid gallons bought there. A negative number is a credit.
4. Tax due or credit = net taxable gallons × the jurisdiction's rate for the quarter.
5. Surcharge, where a jurisdiction lists one = taxable gallons × the surcharge rate. Fuel bought there does not reduce it, so it is always an amount due.

Worked example from a state return

The Missouri Department of Transportation prints this example row on its IFTA quarterly return: 159 taxable miles at a fleet MPG of 4.23 is 38 taxable gallons. With 50 tax-paid gallons bought in the state, net taxable gallons are (12). At the form's example rate of $0.220 per gallon that is a credit of $2.64. Its surcharge example uses 5.0 MPG: 1,250 miles is 250 taxable gallons, 400 gallons bought leaves a net of (150) and a $15.00 credit at a rate of $0.10, while a $0.05 surcharge on all 250 gallons adds $12.50 due. The rates in those examples are the form's own illustrations, not current rates.

Method checked against: West Virginia Tax Division, Instructions for Completion of the IFTA Return; Missouri Department of Transportation, IFTA Quarterly Tax Return (form and instructions).

What this estimate leaves out

• Fuels other than diesel, exempt miles, interest and penalties.
• Jurisdictions where the matrix lists more than one diesel rate for the quarter, or none. They are shown as not computed rather than guessed.
• Rate changes after November 10, 2026. When we retrieved it, IFTA, Inc. listed the Q4 2026 matrix as not final until December 4, 2026. Check the rate sheet your base jurisdiction gives you before you file.