How to Calculate IFTA in 2026: A Step-by-Step Guide for Owner-Operators

If you run interstate, the International Fuel Tax Agreement (IFTA) report is probably the paperwork you dread most. The good news: the math behind it never actually changes. Once you understand the five moving parts (total miles, taxable miles per state, total gallons, fleet MPG, and each state's tax rate), the whole thing becomes a fill-in-the-blanks exercise. This guide walks you through exactly how to calculate IFTA in 2026, with a full worked example across four states so you can see every number land.

What IFTA actually does

IFTA exists so you only file fuel tax in one place (your base state) instead of dealing with every state you drove through. The agreement covers the 48 contiguous US states and 10 Canadian provinces. You qualify if you operate a qualified motor vehicle across state lines, which generally means a truck over 26,000 pounds gross weight or one with three or more axles.

Here is the core idea: every state wants tax on the fuel you burned inside its borders, not on the fuel you bought there. When you fill up, you already pay that state's fuel tax at the pump. IFTA reconciles the difference. If you burned more fuel in a state than you bought there, you owe that state. If you bought more than you burned, you get a credit. Add it all up and you either cut one check or carry a credit forward.

The records you need before you calculate

You cannot do this math from memory. Pull these together for the quarter first:

• Total miles driven in every jurisdiction. Track miles state by state, including any miles run empty or on personal time. Trip sheets, your ELD report, or GPS logs all work.
• Every fuel receipt. You need the gallons purchased and the state where each purchase happened. Keep the actual receipts; states audit IFTA.
• Total gallons purchased across all states for the quarter.

One note on "taxable miles." Most of your miles are taxable, but some states let you deduct specific non-taxable mileage (certain toll roads, fuel-trip-permit miles, or off-highway use). For most owner-operators running standard interstate freight, total miles and taxable miles are the same number. Check your base state's rules if you think you have an exemption.

How to calculate IFTA step by step

Step 1: Add up total miles and total gallons

Sum every mile you drove this quarter across all states. Then sum every gallon you bought across all states. These two fleet-wide totals drive everything else.

Step 2: Calculate your average fleet MPG

Divide total miles by total gallons. This is your fuel economy for the quarter, and IFTA uses it to estimate how much fuel you burned in each state.

Fleet MPG = Total Miles ÷ Total Gallons

Round to two decimals. A loaded sleeper cab pulling a dry van usually lands somewhere around 6 to 7 MPG, so do not panic if your number looks low. That is normal for a Class 8 truck.

Step 3: Calculate taxable gallons burned in each state

For each state, divide the miles you drove there by your fleet MPG. That tells you how many gallons IFTA says you burned in that state.

Taxable Gallons (per state) = State Miles ÷ Fleet MPG

Step 4: Compare gallons burned to gallons bought

For each state, take the taxable gallons you burned and subtract the gallons you actually purchased in that state. A positive number means you burned more than you bought, so you owe. A negative number means you bought more than you burned, so you have a credit coming.

Net Taxable Gallons = Gallons Burned − Gallons Purchased

Step 5: Multiply by each state's current tax rate

Multiply the net taxable gallons in each state by that state's diesel tax rate for the quarter. This is where you absolutely must pull the live numbers (more on that below). The result is the tax owed (positive) or credit (negative) for that state.

Step 6: Add it all up

Total the tax owed and credits across every state. The sum is your net IFTA liability for the quarter. Positive means you write a check. Negative means you carry a credit.

A worked example across four states

Let's run a real quarter. Say you drove a total of 12,000 miles and bought 1,900 gallons of diesel.

Step 1 and 2: Fleet MPG = 12,000 ÷ 1,900 = 6.32 MPG.

Now break the quarter down by state. The rates below are 2026 IFTA diesel rates for these jurisdictions, used here purely as an example. Always confirm the exact figures for your filing quarter on the official matrix.

State	Miles driven	Gallons burned (miles ÷ 6.32)	Gallons bought	Net taxable gallons	Rate	Tax owed / (credit)
Texas	4,000	633.0	800	(167.0)	$0.2000	($33.40)
Illinois	3,000	474.7	300	174.7	$0.7380	$128.93
Indiana	2,500	395.6	400	(4.4)	$0.6300	($2.77)
Pennsylvania	2,500	395.6	400	(4.4)	$0.7410	($3.26)

Add the last column: ($33.40) + $128.93 + ($2.77) + ($3.26) = $89.50 owed on the base lines.

Notice what is happening. You bought a lot of cheap diesel in Texas but barely drove there relative to your fuel buy, so Texas owes you a small credit. You burned a stack of fuel in Illinois without buying much there, so Illinois is where most of your bill comes from. That is the entire logic of IFTA in one table: buy your fuel where the tax is low, and the math still catches up with you in the high-tax states you drive through.

Surcharge states get a separate line

Three states (Indiana, Kentucky, and Virginia) charge a diesel surcharge on top of the regular fuel tax. This trips up a lot of new owner-operators, so read this part twice.

The surcharge works differently from the base tax. The base tax is calculated on your net taxable gallons (burned minus bought), so you can get a credit. The surcharge is calculated on all the gallons you burned in that state, with no credit for fuel you purchased there. You cannot pay a surcharge at the pump, so you always owe it on your return, and it always goes on a separate line from that state's base tax.

Back to our example. You burned 395.6 gallons in Indiana. The 2026 Indiana surcharge is $0.61 per gallon, charged on every gallon burned:

• Indiana surcharge: 395.6 gallons × $0.61 = $241.32 (separate line, owed in full)

So your true Indiana total is the base line ($2.77 credit) plus the surcharge line ($241.32 owed). Add that surcharge to the $89.50 from the base lines and your real net liability for the quarter is about $331 owed. Miss the surcharge line and your return is wrong, and the state will catch it. If you run Kentucky or Virginia, the same separate-line rule applies at each state's own surcharge rate.

Rates change every quarter, so pull the live matrix

Here is the single most important habit for filing IFTA correctly: do not reuse last quarter's rates. IFTA fuel tax rates are updated every quarter, taking effect at the start of January, April, July, and October. A handful of states adjust their diesel rate or surcharge nearly every cycle.

The authoritative source is the official IFTA Inc. tax rate matrix at iftach.org. Before you file, download the matrix for the exact quarter you are reporting, not the quarter you happen to be filing in. If you file your January-to-March return at the end of April, you still use the first-quarter rates, even if second-quarter rates are already published.

When IFTA is due in 2026

IFTA is filed quarterly, even when you owe nothing. The 2026 deadlines are:

• Q1 (Jan to Mar): due April 30
• Q2 (Apr to Jun): due July 31
• Q3 (Jul to Sep): due October 31
• Q4 (Oct to Dec): due January 31

If a deadline lands on a weekend or holiday, it rolls to the next business day. File even on a quarter where you drove very little. A "zero return" is still required, and skipping it carries the same penalty as skipping a normal one, typically $50 or 10% of the tax due, whichever is greater, plus interest.

The fastest way to never dread this again

None of this math is hard. It is just tedious and unforgiving, and a single transposed mileage number or a forgotten surcharge line can throw off the whole return. That is exactly the kind of repetitive, error-prone work a spreadsheet should handle for you.

The 1099 Sheets owner-operator trucking spreadsheet has an IFTA tab that runs every step on this page automatically. You enter your miles by state and your fuel receipts, and it calculates your fleet MPG, taxable gallons, net gallons per state, and the surcharge lines for Indiana, Kentucky, and Virginia without you touching a formula. It works in both Excel and Google Sheets, tracks the rest of your trucking income and expenses for tax time too, and it is a one-time $29. No subscription, no app login, no monthly fee. Buy it once, it is yours forever. Get the 1099 Sheets owner-operator trucking spreadsheet for a one-time $29 and let the IFTA tab do the math for you, this quarter and every quarter after.