How to Calculate IFTA Fuel Tax

IFTA sounds complicated, but the math is the same every quarter. You figure out how much fuel you burned in each state, owe each state its tax on that fuel, and subtract the tax you already paid at the pump there. The return adds it all up into one payment (or credit) with your base state.

What you need from the quarter

• Miles by state or province for every qualified truck, from your ELD or trip sheets. Count all miles, loaded and empty.
• Gallons bought by state, from fuel receipts. These are your tax-paid gallons: the state's fuel tax was in the pump price.
• Total gallons used for the quarter (normally all the fuel you bought, plus any bulk fuel).
• That quarter's tax rates. IFTA, Inc. publishes a new rate matrix every quarter. Use the one for the quarter you're filing, not today's.

The four steps

1. Fleet MPG = total miles ÷ total gallons. The standard IFTA return rounds it to two decimals.
2. Taxable gallons in each state = miles in that state ÷ fleet MPG, rounded to whole gallons.
3. Net tax for each state = taxable gallons × rate − tax-paid gallons × rate. Positive means you owe that state. Negative means a credit.
4. Add up every state. That total is what you pay your base jurisdiction, or the credit it owes you.

IFTA treats your fuel as if you burned it evenly over every mile. So the tax follows your miles, not your fuel stops. The Procedures Manual lists these exact fields for every IFTA return (total distance, total fuel, average MPG, taxable gallons, tax-paid gallons, and tax due by jurisdiction), and the Articles of Agreement give you full credit for tax-paid fuel as long as you keep the receipts.

Worked example: one truck, 3rd quarter 2026

Say you ran 11,500 miles last quarter and used 1,770 gallons. Here's where you drove and where you fueled:

• Texas: 4,200 miles, 600 gallons bought (rate $0.2000)
• Oklahoma: 1,800 miles, 450 gallons bought (rate $0.1900)
• Arkansas: 1,500 miles, 0 gallons bought (rate $0.2850)
• Tennessee: 2,100 miles, 400 gallons bought (rate $0.2700)
• Kentucky: 900 miles, 0 gallons bought (rate $0.2200 + $0.1050 surcharge)
• Virginia: 1,000 miles, 320 gallons bought (rate $0.3360 + $0.1430 surcharge)

Step 1. Fleet MPG = 11,500 ÷ 1,770 = 6.50 MPG.

Step 2 and 3 for Texas. Taxable gallons = 4,200 ÷ 6.50 = 646. You bought 600 there, so Texas gets tax on 46 more gallons: 646 × $0.2000 − 600 × $0.2000 = $9.20 owed.

Oklahoma goes the other way. Taxable gallons = 1,800 ÷ 6.50 = 277, but you bought 450 there. That's 173 gallons you paid Oklahoma tax on but burned somewhere else, so Oklahoma owes you $32.87.

Surcharge states: Kentucky and Virginia

The IFTA rate matrix lists a separate surcharge for Kentucky and Virginia. Both states charge it on every gallon used on their roads, and the credit for fuel bought there is only at the regular rate. Kentucky's law (KRS 138.660 and 138.695) and Virginia's (Code § 58.1-2701 and § 58.1-2706) both work this way.

In the example, Kentucky: 138 taxable gallons × $0.2200 = $30.36, plus 138 × $0.1050 surcharge = $14.49. No fuel bought there, so you owe $44.85.

Virginia: 154 × $0.3360 = $51.74 tax, plus 154 × $0.1430 = $22.02 surcharge, minus a credit of 320 × $0.3360 = $107.52. Net: -$33.76. Even though you bought more fuel in Virginia than you burned there, the surcharge keeps the credit smaller than it would be.

The total

Do the same for every state and add the lines:

• Texas: $9.20
• Oklahoma: -$32.87
• Arkansas: $65.84
• Tennessee: -$20.79
• Kentucky: $44.85
• Virginia: -$33.76

The total is $32.47 due with the return. Notice that the credits from Oklahoma, Tennessee, and Virginia cancel most of what you owe Texas, Arkansas, and Kentucky. That's normal. IFTA mostly moves tax between states. You only pay extra when you burn more fuel in a state than you buy there.

Mistakes that cost money

• Using the wrong quarter's rates. Rates change every quarter, and a few cents a gallon adds up. Check the matrix for your quarter on the IFTA rates by state page.
• Missing receipts. No receipt, no credit. A lost $500 fill-up in a high-tax state can cost you real money at the end of the quarter.
• Leaving out miles. States with no fuel tax on your return (like Oregon, where trucks pay a weight-mile tax instead) still count in total miles. Leaving them out throws off your MPG and every other line.
• Forgetting to file. You owe a return for every quarter you hold an IFTA license (Articles of Agreement R910), even a slow one.

Plug your own quarter into the IFTA fuel tax calculator and it does all of this with the right quarter's rates. Keep your miles organized with the trip sheet generator, and see what a run will cost in fuel with the trip fuel cost calculator.