This is the hands-on companion to IFTA Explained, which covers who needs IFTA and when it is due. To run your own quarter, use the IFTA fuel tax calculator.
What you need before you start
Two numbers for every state you drove in, for the whole quarter:
- Miles driven in that state, from your ELD state-mileage report or trip sheets with odometer readings at each state line. Count every mile: loaded, empty, bobtail and personal.
- Tax-paid gallons bought in that state, from fuel receipts showing the date, seller, location and gallons.
The example: one truck, three states
An owner-operator running Texas–Illinois lanes from October to December 2026. He fuels where diesel is cheapest and takes on as little as he can in Illinois.
| State | Miles driven | Gallons bought |
|---|---|---|
| Texas | 9,500 | 1,400 |
| Oklahoma | 4,200 | 600 |
| Illinois | 6,300 | 120 |
| Total | 20,000 | 2,120 |
Step 1: Fleet MPG
Total miles ÷ total gallons, all states combined: 20,000 ÷ 2,120 = 9.43 MPG. Use this fleet-wide figure, not the dashboard MPG, and keep two decimals.
Step 2: Taxable gallons per state
Miles in each state ÷ fleet MPG. This is the fuel you burned on that state's roads.
| State | Miles | ÷ 9.43 MPG |
|---|---|---|
| Texas | 9,500 | 1,007 gal |
| Oklahoma | 4,200 | 445 gal |
| Illinois | 6,300 | 668 gal |
Step 3: Net gallons per state
Taxable gallons − gallons bought there. Positive means you burned more than you bought; negative means you bought more than you burned.
| State | Taxable | Bought | Net |
|---|---|---|---|
| Texas | 1,007 | 1,400 | −393 |
| Oklahoma | 445 | 600 | −155 |
| Illinois | 668 | 120 | +548 |
Step 4: Multiply by each state's rate
Q4 2026 diesel rates, effective October 1, 2026: Texas $0.20, Oklahoma $0.19, Illinois $0.738 per gallon. Rates change every quarter, so check the current IFTA matrix before filing.
| State | Net gal | × Rate | Tax |
|---|---|---|---|
| Texas | −393 | $0.200 | −$78.60 |
| Oklahoma | −155 | $0.190 | −$29.45 |
| Illinois | +548 | $0.738 | +$404.42 |
| Total owed | $296.37 |
He pays $296.37 with his Q4 return, due January 31. The Texas and Oklahoma credits trimmed $108 off the Illinois bill, nowhere near all of it.
Why he owes: the fuel-buying trap
Cheap pump prices in Texas and Oklahoma look good, but their fuel tax is low, so each gallon bought there earns only a 19–20¢ credit. Every gallon burned in Illinois costs 73.8¢. Running 548 gallons short in Illinois is what created the bill.
Compare pump price minus fuel tax, not the price on the sign. Illinois diesel at $3.95 with 73.8¢ of tax has a base price of $3.21. Texas diesel at $3.45 with 20¢ of tax is really $3.25. The Illinois gallon is cheaper, and buying it would have erased most of this return. The fuel cost calculator makes that comparison for you.
Surcharge states
Indiana, Kentucky and Virginia add a surcharge on top of the base rate. It applies to every taxable gallon burned there, with no credit for fuel bought in the state. In Kentucky (Q4 2026: $0.22 base + $0.105 surcharge) you work the base rate as above, then add 10.5¢ × taxable gallons as a separate line. Expect to owe something in a surcharge state even if you filled up there.
Common mistakes
- Using dashboard MPG instead of total miles ÷ total gallons. Small errors here shift gallons into every state.
- Dropping deadhead, bobtail or personal miles. IFTA counts all miles, not just loaded ones.
- Counting reefer fuel. Fuel for the refrigeration unit is not propulsion fuel. Keep it on separate receipts.
- Missing receipts. No receipt, no credit. The miles still count, so you pay tax twice on that fuel.
- Rounding too early. Keep decimals on MPG and gallons until the final tax line.
Enter your miles and gallons by state in the IFTA fuel tax calculator. It carries current rates, handles surcharge states and shows the same four steps so you can check it against your return.
Common questions
Do I calculate IFTA per truck or for the whole fleet?
For the whole fleet. Add up miles and gallons for every qualified truck under your IFTA license and work out one fleet MPG. Keep miles by state and fuel receipts for each truck in case of an audit.
Why do I owe IFTA in a state where I never bought fuel?
IFTA taxes the fuel you burn, not the fuel you buy. Miles driven in a state create taxable gallons there even if every receipt is from somewhere else.
What if my IFTA total is negative?
You bought more tax-paid fuel than you burned. The credit is refunded by your base state or carried forward to the next quarter, depending on your state's rules.