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Methodology

What this calculator does

IFTA HQ estimates the quarterly fuel use tax for one fuel type, in miles, gallons, and US dollars, following the layout of the IFTA quarterly schedule that base jurisdictions publish. Every figure is calculated in your browser from the miles and gallons you enter and the tax rates for the quarter you select.

The steps below are the same ones shown under Show the math and printed on the PDF worksheet.

Step 1: Totals and fleet MPG

Miles and gallons are reported as whole numbers, rounded to the nearest whole number (1,234.5 becomes 1,235). If you enter several rows for the same jurisdiction, the rows are added together first and the total is rounded once, because the return has one line per jurisdiction.

Total miles include miles in IFTA jurisdictions and in non-IFTA jurisdictions. Total gallons include all fuel placed in the vehicle's tank, wherever it was purchased.

Fleet MPG is total miles divided by total gallons, rounded to two decimal places (4.567 becomes 4.57). One MPG figure is used for every jurisdiction.

Step 2: Taxable gallons for each jurisdiction

Taxable gallons are the jurisdiction's taxable miles divided by fleet MPG, rounded to a whole number. If you do not enter taxable miles separately, all miles in the jurisdiction are treated as taxable.

Net taxable gallons are taxable gallons minus the tax-paid gallons you purchased in that jurisdiction. When you bought more fuel in a jurisdiction than you used there, the result is negative and becomes a credit.

Step 3: Tax for each jurisdiction

Tax is net taxable gallons multiplied by the jurisdiction's rate for the fuel type and quarter. Each line is rounded to the cent and then the lines are added up. Credits appear in parentheses on the worksheet.

The instructions we checked do not say which way to round an amount that ends in exactly half a cent. This calculator rounds it away from zero, for tax due and credits alike. A base jurisdiction's online filing system may differ by a cent on a line.

Surcharges

A few jurisdictions charge a surcharge in addition to fuel tax. In the third quarter of 2026, Kentucky and Virginia charge a surcharge on diesel. The rate table records which jurisdictions have one for each fuel type, so the calculator does not depend on a fixed list.

The surcharge is calculated on taxable gallons, not net taxable gallons, and fuel purchased in the jurisdiction cannot reduce it. It is therefore never a credit, even when the fuel tax line for the same jurisdiction is. This is one of the most common mistakes on a hand-prepared return, so the worksheet shows the surcharge as a separate step.

Non-IFTA jurisdictions and rates shown as N/A

Alaska, Hawaii, the District of Columbia, Yukon, the Northwest Territories, Nunavut, and Mexico are not IFTA members. Miles driven and fuel purchased there count toward total miles, total gallons, and fleet MPG, but no IFTA tax line is calculated for them.

Some member jurisdictions have no IFTA rate for a fuel type. For example, Oregon taxes heavy trucks with a weight-mile tax instead. Those miles still count toward fleet MPG and still produce taxable gallons, but the tax on that line is $0.00.

Due dates

A quarterly return is due on the last day of the month after the quarter ends: April 30, July 31, October 31, and January 31. When that day falls on a weekend or a holiday, the return is due the next business day. For the third quarter of 2026, October 31 is a Saturday, so the return is due Monday, November 2, 2026.

The calculator moves a due date only for weekends. None of these four dates, and none of the days they can move to, is a federal holiday. Check your base jurisdiction's calendar for state holidays.

Where the tax rates come from

Each quarter's rates are compiled from two state agency publications of the quarterly IFTA rate tables: Forms IFTA-105 and IFTA-105.1 from the New York State Department of Taxation and Finance, and Form GAS-1278 from the North Carolina Department of Revenue. The two are compared cell by cell for every jurisdiction and fuel type. A quarter is published here only when every cell matches.

The worksheet shows the quarter, the sources, and the date the rates were retrieved. Rates can be corrected after publication, and we recheck them monthly. Always confirm the rates against your base jurisdiction's return before filing.

The calculation steps were checked against the quarterly return instructions published by New York, Georgia, Idaho, New Jersey, Delaware, and Tennessee, which describe the same method.

What this calculator does not handle yet

Electricity and hydrogen. Some jurisdictions tax these by distance instead of by gallon, which is a different formula.

Rate changes during a quarter. When a jurisdiction changes its rate partway through a quarter, the return splits that jurisdiction into two lines. This calculator uses the rate in effect at the start of the quarter and shows a note when this applies.

Untaxed fuel. All fuel you enter as purchased is treated as tax-paid. Fuel from bulk storage that was purchased without tax is not handled.

Interest and penalties for late returns.

Carriers based in Canada, who report in litres and Canadian dollars. The base jurisdiction list covers the 48 contiguous US states.

Trip permit miles. Leave them out of the taxable miles you enter for that jurisdiction.

Different rounding in Tennessee. Tennessee's instructions describe dropping the third decimal of MPG instead of rounding it, and rounding tax amounts in two stages. This calculator follows the rounding used by most jurisdictions, so a Tennessee-based return can differ by 0.01 MPG or $0.01 on a line.

Sources