How IFTA Tax Is Calculated

IFTA looks complicated because the return has so many columns, but the arithmetic underneath is one formula applied jurisdiction by jurisdiction. Understanding it matters even if software does the math, because the single most consequential input — your fleet fuel consumption factor — is derived from records you have to keep correctly all quarter.

A terminology note before the steps: the 2026 manuals say "average fuel consumption factor" and "volume" rather than MPG and gallons, because the Agreement now covers electricity, diesel gallon equivalents and gasoline gallon equivalents alongside liquid fuel. This page uses MPG and gallons for readability.

The computation, step by step

Every IFTA return follows this sequence:

Total distance — all miles travelled during the period by every qualified vehicle in the fleet, whether the miles are taxable or not. This includes miles in non-IFTA jurisdictions and miles run under a trip permit.
Total fuel — every drop placed into the supply tanks of qualified vehicles, receipted or not, taxed or not.
Average fleet MPG — total distance divided by total fuel, rounded to two decimal places. One factor for the whole fleet per fuel type, not one per truck.
Taxable distance per jurisdiction — in-jurisdiction distance, which excludes fuel-tax-trip-permit miles and miles a jurisdiction exempts from fuel taxation.
Taxable gallons per jurisdiction — taxable distance divided by the fleet MPG.
Tax-paid gallons per jurisdiction — fuel bought at retail in that jurisdiction with that jurisdiction’s tax already in the pump price, plus qualifying bulk withdrawals.
Net taxable gallons — taxable gallons minus tax-paid gallons. Positive means you owe; negative is a credit.
Tax due per jurisdiction — net taxable gallons multiplied by that jurisdiction’s rate for that fuel type for that quarter.
Surcharge line where applicable — computed on a different basis, covered below.
Sum everything into one net figure, paid to the base jurisdiction only.

The Agreement is explicit that this discharges you everywhere: timely filing of the return and payment of taxes due to the base jurisdiction for all member jurisdictions discharges the licensee’s responsibility for filing returns and paying individual taxes to all member jurisdictions.

A worked example

This example is constructed to demonstrate the method — the miles and gallons are invented, though the rates are real ones from the third-quarter 2026 rate matrix. Rates change every quarter, so always pull the live matrix rather than reusing figures from an article.

A diesel fleet runs 20,000 total miles in the quarter and puts 2,200 gallons into its tanks. Average fleet MPG is 20,000 divided by 2,200, which is 9.09 after rounding to two decimals.

Now per jurisdiction. In Ohio the fleet ran 8,000 taxable miles, which is 880 taxable gallons, but bought 1,200 gallons there — a credit of 320 gallons at $0.4700, or minus $150.40. In Pennsylvania, 6,000 miles is 660 gallons against 700 purchased, a credit of $29.64. In Kentucky, 4,000 miles is 440 gallons against 300 purchased, so 140 gallons are owed at $0.2200, which is $30.80. In Indiana, 2,000 miles is 220 gallons with no fuel bought there, so 220 gallons at $0.6300, or $138.60.

Add the Kentucky surcharge — 440 gallons at $0.1050, which is $46.20 — and the return nets to about $35.56 owed. Notice what that surcharge did: it exceeded Kentucky’s own base tax, because of how surcharges work.

The surcharge line is charged gross, with no credit

Three jurisdictions carry a surcharge line on the IFTA rate matrix: Indiana, Kentucky and Virginia. The surcharge is computed on a different basis than every other line on the return — it is taxable gallons multiplied by the surcharge rate, gross, with no subtraction for fuel purchased in that state.

The reason is mechanical: a surcharge is never collected at the pump, so there is nothing to credit. Filing instructions make this explicit by requiring a zero in the tax-paid column on any surcharge line, and by taking the taxable gallons figure straight from the jurisdiction’s regular fuel-tax line. This is why carriers who run heavily in surcharge states owe money even when their fuel buying looks perfectly balanced — as the Kentucky line in the example above shows.

One current nuance worth knowing, because most published guidance has not caught up: Indiana repealed its motor carrier surcharge tax effective July 1, 2018 and folded it into the special fuel rate. Its surcharge row on the matrix now carries only an alternative-fuel rate, so for diesel fleets in practice only Kentucky and Virginia produce a surcharge liability. Read the surcharge line off the current quarter’s matrix rather than working from a list.

What counts as taxable distance

In-jurisdiction distance is the total miles operated by your qualified vehicles within a jurisdiction, including miles operated under an IFTA temporary decal permit. It does not include miles operated on a fuel tax trip permit, or miles exempted from fuel taxation by that jurisdiction.

Total distance is broader: all miles travelled during the period by every qualified vehicle in the fleet, regardless of whether any jurisdiction treats them as taxable. That difference is the source of a common return error — leaving trip-permit or non-IFTA miles out of total distance inflates your fleet MPG, which then understates taxable gallons in every jurisdiction at once.

Exempt-mile definitions are set by each jurisdiction, not by IFTA, and you are required to obtain the definitions from the jurisdictions themselves. Do not assume a category exempt in one state is exempt in the next.

Frequently asked questions

How is the IFTA fuel tax calculated?⌄

Divide total distance by total fuel to get your average fleet MPG, rounded to two decimals. For each jurisdiction, divide taxable distance by that MPG to get taxable gallons, subtract the gallons you bought there with tax paid, and multiply the difference by that jurisdiction’s rate for the quarter. Net it all together into one payment to your base jurisdiction.

Why do I owe money to a state where I bought fuel?⌄

Most often a surcharge. Surcharges are calculated on gross taxable gallons with no credit for fuel purchased, because the surcharge is never collected at the pump. It is entirely possible for a surcharge line to exceed the base tax for the same state, as it does in the worked example on this page.

Is fleet MPG calculated per truck?⌄

No — one average fuel consumption factor covers the whole fleet for each fuel type, calculated from total distance and total fuel and rounded to two decimal places. That is why one truck’s missing mileage records distorts the return for every jurisdiction.

Do trip permit miles go on the IFTA return?⌄

They belong in total distance but not in taxable distance. Fuel-tax-trip-permit miles are excluded from in-jurisdiction (taxable) distance, while total distance covers all miles regardless of taxability. Omitting them from total distance inflates your fleet MPG and distorts the entire return.

Where do I get current IFTA tax rates?⌄

From the quarterly tax rate matrix published by IFTA, Inc. Rates change every quarter, and surcharge lines change too, so pull the matrix for the quarter you are filing rather than reusing rates from a previous return or an article.

Related guides

Official sources

Agency rules, fees and contacts can change — confirm current requirements with the agency before acting. This guide is general information for truckers, not tax or legal advice.

How IFTA Tax Is Actually Calculated