How do I calculate IFTA miles per gallon?

Total miles in all jurisdictions divided by total gallons placed in the trucks, rounded to 2 decimals. In the sample, 8,080 miles / 1,240 gallons = 6.52 MPG.

How do I calculate IFTA tax-paid gallons?

Add the gallons on your fuel receipts for each jurisdiction where the price included that jurisdiction's fuel tax. Credit for tax-paid fuel needs a receipt, invoice, credit card receipt or vendor transaction listing, and only for fuel placed in a qualified motor vehicle with the member jurisdiction's tax in the price.

What does a negative IFTA line mean?

You bought more tax-paid fuel there than you used there. In the sample, Oklahoma has 218 taxable gallons and 480 tax-paid gallons, so -262 net gallons and -$49.78: a credit against what you owe elsewhere.

How is the Kentucky or Virginia surcharge calculated?

Surcharge (surtax) lines for Kentucky, Indiana and Virginia: the taxable gallons of the tax line, zero tax-paid gallons, so the surcharge is due on every taxable gallon and is never a credit. In the sample, Virginia's 98 taxable gallons x $0.1430 = $14.01.

Do I need IFTA software to calculate it?

No. The maths is four lines per jurisdiction; the work is collecting miles by state and fuel receipts. The free calculator does the arithmetic with the current matrix rates.

How to calculate IFTA tax, step by step (with a worked example)

IFTA tax is worked out per jurisdiction in four steps: fleet MPG = total miles / total gallons; taxable gallons = the jurisdiction's taxable miles / MPG; net taxable gallons = taxable gallons - the tax-paid gallons you bought there; tax = net taxable gallons x the jurisdiction's rate for the quarter, plus any surcharge on the taxable gallons. Add the lines: positive is owed with the return, negative is a credit. Below, one sample quarter (8,080 miles, 5 states) worked through with 3rd quarter 2026 rates.

Open the ifta tax calculator

Step 1: fleet MPG

Add every mile driven by your qualified trucks in every jurisdiction for the quarter, add every gallon put in them, and divide. The return wants it to 2 decimals (IFTA Procedures Manual P720.350). Sample data: 8,080 miles and 1,240 gallons give 6.52 MPG.

Step 2: taxable gallons per jurisdiction

Divide each jurisdiction's taxable miles by the MPG and round to a whole gallon. Oklahoma: 1,420 miles / 6.52 = 218 taxable gallons. That is the fuel the return says you burned there, whatever you bought there.

Step 3: subtract the tax-paid gallons

Net taxable gallons = taxable gallons - tax-paid gallons bought in that jurisdiction. No fuel was bought in Virginia, so all 98 gallons are net taxable. In Oklahoma, 480 gallons were bought against 218 used: -262 net, a credit.

Step 4: rate, surcharge and total

Multiply net taxable gallons by the jurisdiction's rate for the quarter from the IFTA, Inc. matrix. Kentucky and Virginia list a diesel surcharge in 3Q2026: it is charged on the taxable gallons, with no tax-paid credit. The table is the whole sample quarter:

Sample data: one diesel truck, 3Q2026 rates, 6.52 MPG (computed)
State	Taxable mi	Taxable gal	Tax-paid gal	Net gal	Rate	Tax + surcharge
TX	3,850	590	520	70	$0.2000	$14.00
OK	1,420	218	480	-262	$0.1900	-$49.78
AR	960	147	100	47	$0.2850	$13.40
TN	1,210	186	140	46	$0.2700	$12.42
VA	640	98	0	98	$0.3360 + $0.1430	$46.94
Total	8,080	1,239	1,240	-1		$36.98

Type your own quarter in the IFTA tax calculator: it applies the same four steps to every jurisdiction with the matrix rates, and keeps the numbers in your browser.

Frequently asked questions

How do I calculate IFTA miles per gallon?: Total miles in all jurisdictions divided by total gallons placed in the trucks, rounded to 2 decimals. In the sample, 8,080 miles / 1,240 gallons = 6.52 MPG.
How do I calculate IFTA tax-paid gallons?: Add the gallons on your fuel receipts for each jurisdiction where the price included that jurisdiction's fuel tax. Credit for tax-paid fuel needs a receipt, invoice, credit card receipt or vendor transaction listing, and only for fuel placed in a qualified motor vehicle with the member jurisdiction's tax in the price.
What does a negative IFTA line mean?: You bought more tax-paid fuel there than you used there. In the sample, Oklahoma has 218 taxable gallons and 480 tax-paid gallons, so -262 net gallons and -$49.78: a credit against what you owe elsewhere.
How is the Kentucky or Virginia surcharge calculated?: Surcharge (surtax) lines for Kentucky, Indiana and Virginia: the taxable gallons of the tax line, zero tax-paid gallons, so the surcharge is due on every taxable gallon and is never a credit. In the sample, Virginia's 98 taxable gallons x $0.1430 = $14.01.
Do I need IFTA software to calculate it?: No. The maths is four lines per jurisdiction; the work is collecting miles by state and fuel receipts. The free calculator does the arithmetic with the current matrix rates.

IFTA fuel tax rates, 3rd quarter 2026: diesel and gasoline by state
Diesel and gasoline rates for all 58 IFTA jurisdictions in 3Q2026 from the IFTA, Inc. matrix, with the Kentucky and Virginia surcharges and the top 10.
IFTA due dates 2026 and 2027: the quarterly filing calendar
Every IFTA quarterly return due date for 2026 and 2027, moved past weekends as R960 says, with the late penalty ($50 or 10%) and interest rules.
What records do you need to keep for IFTA?
The trip and fuel receipt fields the IFTA Procedures Manual lists, how long to keep them (four years) and why the MPG on the return must match them.

Last updated 2026-09-29. Estimates from the IFTA, Inc. tax rate matrix for the quarter shown. Not tax advice. File your return with your base jurisdiction and check its figures. Not affiliated with IFTA, Inc.