HOW TO USE THIS CALCULATOR
- Add a row for each state you drove or bought fuel in. Type the state name. This page does not fill in a rate for you.
- Enter taxable miles and the gallons the truck used in that state. Enter gallons of tax-paid fuel you purchased there. A blank purchase box counts as 0.
- If you only know total gallons for the quarter, enter that total and use Split by miles. Each state’s gallons used become its share of the miles. You can edit a row after that.
- Open the IFTA, Inc. tax rate matrix, pick the quarter, and type that jurisdiction’s rate. Leave the rate blank if you have not looked it up yet. Those rows still show net gallons and stay out of the tax total.
- Read the result as an estimate. Positive tax is owed. Negative tax is a credit.
A filed IFTA return uses one average MPG: total taxable miles divided by total taxable gallons. Gallons consumed in a state are that state’s miles divided by the average MPG. Split by miles does that split. Net taxable gallons are gallons consumed minus tax-paid gallons purchased. The IFTA Filing Defender spreadsheet uses the same steps, and its rate cells start empty.
A WORKED EXAMPLE
Example only. Not a quarter you ran, and not a tax rate. The $0.25 figure is a stand-in so the multiplication is easy to check. Look up the real rate on the IFTA matrix before you rely on a result.
North: 1,000 miles, 200 gallons used, 250 gallons purchased, rate 0.25. Net taxable gallons = 200 − 250 = −50. Estimated tax = −50 × 0.25 = −$12.50 (a credit).
South: 1,000 miles, 200 gallons used, 100 gallons purchased, rate 0.25. Net taxable gallons = 200 − 100 = 100. Estimated tax = 100 × 0.25 = $25.00 owed.
Together: 2,000 miles, 400 gallons used, average MPG = 2,000 ÷ 400 = 5.00. Net taxable gallons = 50. Estimated tax owed = $25.00 − $12.50 = $12.50. Change any input and the estimate changes.