IFTA fuel tax calculator — by state, with the return's own rules
How is IFTA fuel tax actually calculated by state?
One fleet MPG first: on the worked example here, 5,400 total miles everywhere divided by 850 gallons bought everywhere gives 6.35, rounded to two decimals. Each state's taxable gallons are its taxable miles divided by that MPG; subtract the gallons you bought there, multiply by the state's rate, and negative lines are credits that offset the other states on the same return — the example closes at $61.75 owed once the Kentucky surcharge is added on full gallons.
United States and Canadian IFTA jurisdictions · diesel · one fuel type per return · runs in your browser, nothing is sent anywhere
Every IFTA calculator in the search results multiplies miles by a rate. The quarterly return does not work that way: your fleet MPG is rounded to two decimals before anything else, each state's taxable gallons come from where you DROVE rather than where you bought fuel, credits offset debts inside the same return, and three states add a surcharge that ignores the fuel you paid for at the pump. This page computes all of it, line by line, and shows the arithmetic.
Your quarter
Alaska, Hawaii, the territories and Mexico are not IFTA jurisdictions: miles and fuel there still count toward your fleet MPG, but they get no line on the return.
Pre-filled rates are the final Q2 2026 diesel rates from Form IFTA-105 (New York State), captured 2026-09-02. The rate field is editable — before filing, replace it with your own quarter's rate from the official table.
The quarter now running is Q3 2026 and these pre-filled rates are Q2 2026. IFTA publishes a new rate table every quarter, so replace every rate with the figure from the official table for the quarter you are filing before you use this for a return.
The Kentucky and Virginia surcharge lines are added automatically from the same official table. When the official table publishes no diesel surcharge rate for a listed surcharge jurisdiction, that line is shown as not computed rather than guessed at.
The return, line by line
You owe $61.75 for the quarter across all jurisdictions, credits already netted.
| Jurisdiction | Line | Taxable gallons | Bought there | Net gallons | Rate | Tax |
|---|---|---|---|---|---|---|
| TX | fuel | 504 | 700 | -196 | $0.20 | -$39.20 |
| OH | fuel | 220 | 0 | 220 | $0.47 | $103.40 |
| KY | fuel | 94 | 150 | -56 | $0.22 | -$12.32 |
| KY | surcharge | 94 | — | — | $0.105 | $9.87 |
A negative net-gallons figure is a credit: you bought more fuel there than you consumed there, and the credit — at that state's own rate — offsets what you owe the other states on this same return.
What the return actually does
- One fleet MPG for everything: 5,400 total miles everywhere — including miles outside IFTA jurisdictions — divided by 850 gallons bought everywhere gives 6.35, rounded to two decimal places. That single figure feeds every line below; the rounding alone can move the quarter's tax by real dollars.
- Taxable gallons per jurisdiction: that state's taxable miles divided by the fleet MPG, rounded to a whole gallon. Fuel is taxed where it is CONSUMED, not where it is bought — this is the column most homemade spreadsheets get wrong.
- Net gallons: taxable gallons minus the gallons you bought in that state. Bought more than you consumed there? The line goes negative — a credit at that same state's rate, and it offsets the states you owe on this very return, not in some future refund claim.
- The surcharge in Indiana, Kentucky and Virginia is computed on FULL taxable gallons, with nothing subtracted for fuel bought there — a surcharge cannot be prepaid at the pump, so it is owed even in a quarter where that state's fuel line is a credit.
- It computes one fuel type — diesel. Gasoline, propane and natural gas have their own rates and their own exemptions.
- It does not compute interest on a late return; the interest rule is named in the sources file, but the month-by-month mechanics are not carried here.
- Indiana's surcharge rate is not filled in, because it has not been read from a primary source — that line is marked, never silently skipped or counted as zero.
- Road-use taxes outside IFTA — Kentucky's weight-distance tax, New York's highway use tax, New Mexico's and Oregon's — are separate filings and are not computed here.
- Exempt-mile rules differ by jurisdiction and are not carried: if some of your miles are exempt, you enter the taxable figure yourself in the separate field.
- It fills in no return and files nothing — it shows you the arithmetic your return should contain, so you can check what your service or software produced.
Every rule above — the MPG rounding, the taxable-gallons division, the credit treatment and the surcharge on full gallons — is quoted from the instructions for Form IFTA-101, with the exact wording and URL in the page's sources file, and the arithmetic on this page is verified against an independent model of those rules.
This is arithmetic, not tax advice. Rates change every quarter; verify the rate for your quarter against the official table before filing.
This calculator answers one trip — the workbook runs your quarter
A trip & fuel log deep enough for the whole quarter, rolled up into the columns of Form IFTA-101: credits netted against taxes due, the Kentucky/Virginia surcharge on full gallons even when the fuel line is a credit, every shipped diesel rate from a two-source name-by-name cross-check — quarter and capture date printed on the sheet — and live self-checks to pass before you file.
IFTA Fuel Tax Spreadsheet — $19Questions people actually ask
Why is my taxable-gallons figure different from the gallons I actually bought?
Because they measure different things. Taxable gallons are computed — that state's taxable miles divided by your fleet MPG — and represent the fuel you CONSUMED while driving there. The gallons you bought there only enter afterwards, as a subtraction. A state you crossed without refuelling still gets a tax line; a state where you filled both tanks but barely drove owes you a credit.
Why do I owe a Kentucky surcharge when my Kentucky fuel line is a credit?
Because the surcharge is charged on your full taxable gallons, with no subtraction for fuel bought in the state — you cannot prepay a surcharge at the pump. On the worked example, Kentucky's fuel line is a credit and its surcharge line is still owed. Spreadsheets that compute the surcharge on net gallons understate the return every quarter this happens.
Where do the pre-filled rates come from, and can I file with them?
They are the final Q2 2026 diesel rates as published on Form IFTA-105 by New York State, captured 2026-09-02 — the source and date are printed next to the form. Rates change every quarter, so before filing you should overtype each rate with the figure from the official table for the quarter you are filing. The arithmetic does not change; only the rates do.
Do miles in Alaska, Hawaii or Mexico count?
They count toward your fleet MPG — total miles divided by total gallons uses miles and fuel from everywhere — but they get no jurisdiction line on the return, because those places are not IFTA members. That is what the two separate fields at the bottom of the form are for.
Does the tool see my mileage or fuel figures?
No. The arithmetic runs in your browser, nothing is sent anywhere, and the page works offline once loaded. The worked example you see before typing anything is computed on our server with the same shipped code, from the same example trip.
