How do I calculate IFTA taxable gallons?

Divide the taxable miles in the jurisdiction by your fleet MPG for the quarter and round to a whole gallon. At 6.52 MPG, 1,000 taxable miles are 153 taxable gallons.

Why is my IFTA tax negative in some states?

Because you bought more tax-paid fuel there than you burned there. The net taxable gallons are negative and the line is a credit that offsets the tax owed to other states; a total credit is refunded or carried forward under your base jurisdiction's rules.

Do I include Oregon miles?

Yes: every mile in every jurisdiction goes into the total miles and the MPG. The matrix lists no diesel rate for Oregon this quarter, so the Oregon line carries no tax here.

Which MPG should I use?

One MPG per fuel type for the whole return: all miles divided by all gallons placed in the trucks, two decimals. With several trucks, add their miles and gallons first; the fleet MPG calculator does that.

Can I use this for gasoline trucks?

Yes: pick gasoline, gasohol or biodiesel. Propane, LNG, CNG, alcohol blends, electricity and hydrogen use gallon equivalents or other units each jurisdiction defines, so they are left to your base jurisdiction's return.

Free calculator

IFTA tax calculator

Type the miles you drove and the tax-paid gallons you bought in each state or province this quarter. The calculator works out the fleet MPG, the taxable gallons per jurisdiction, the net gallons after your fuel receipts, the tax and surcharge at the 3rd quarter 2026 rates from the IFTA, Inc. matrix, and the total due or credit.

Sample data: a made-up quarter for one diesel truck, so you can see the result. Replace the lines with your own miles and fuel receipts.

Quarter (rate matrix)Fuel type

Jurisdiction 1

State or provinceTotal milesmiTaxable miles (if different)miEmpty = all miles are taxable. Some states exempt toll roads or off-highway miles.Tax-paid gallons bought heregalFrom your fuel receipts in this jurisdiction.

Jurisdiction 2

Jurisdiction 3

Jurisdiction 4

Jurisdiction 5

Fleet MPG (optional)

All gallons this quartergalEmpty = the tax-paid gallons above. Add bulk fuel or fuel bought outside IFTA jurisdictions.Your MPG (if you have it)Empty = total miles / total gallons, to two decimals.

One MPG for the whole return: fleet MPG calculator for several trucks.

Rates: IFTA, Inc. tax rate matrix 3Q2026, downloaded 2026-09-29 (iftach.org). Your numbers stay in this browser.

Result

Total owed for 3Q2026: $36.98
Fleet MPG: 6.52
Total miles: 8,080 mi
Gallons used for MPG: 1,240 gal
Taxable gallons: 1,239 gal
Tax-paid gallons: 1,240 gal
Fuel tax (net): $22.97
Surcharges: $14.01

Positive = you owe it with the return; negative = a credit (your base jurisdiction decides refund or carry-forward). 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.

Line by line, 3rd quarter 2026, diesel (special fuel), MPG 6.52
Jur.	Taxable gal	Tax-paid gal	Net gal	Rate	Tax + surcharge
TX	590	520	70	$0.2000	$14.00
OK	218	480	-262	$0.1900	-$49.78
AR	147	100	47	$0.2850	$13.40
TN	186	140	46	$0.2700	$12.42
VA	98	0	98	$0.3360+ $0.1430 surcharge	$46.94$32.93 + $14.01
Total	1,239	1,240	-1		$36.98

Rates per gallon from the matrix: TX $0.2000/gal, OK $0.1900/gal, AR $0.2850/gal, TN $0.2700/gal, VA $0.3360/gal.

Filing this quarter? Pro prints the worksheet.

Every jurisdiction line with its rate, the totals and the MPG on one printable sheet, an Excel file with live formulas and trip and fuel logs for next quarter.

See Pro

How it works

MPG = total miles / total gallons, to 2 decimals (IFTA Procedures Manual P720.350). For each jurisdiction, taxable gallons = taxable miles / MPG and net taxable gallons = taxable gallons - tax-paid gallons, both rounded to whole gallons as the return columns are (P720.500). Tax = net taxable gallons x the jurisdiction's rate; a surcharge is due on the taxable gallons, not the net, so it is never a credit. 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.

Sample data: at 6.52 MPG, 3,850 Texas miles are 590 taxable gallons; with 520 gallons bought in Texas the net is 70 gallons, $14.00 at $0.2000. Virginia: 98 taxable gallons, 98 net, $32.93 of tax plus $14.01 of surcharge on all 98 taxable gallons. The whole sample quarter comes to $36.98.

A tax-paid credit needs the receipt: 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. Jurisdictions with no rate listed for the fuel this quarter (OR for diesel) carry no tax here, but their miles still count for MPG.

Sources of the rates and rules

Tax rates, 3Q2026: IFTA, Inc. tax rate matrix 3Q2026 (CSV), downloaded from the IFTA, Inc. Tax Rate Download Center — https://www.iftach.org/taxmatrix/charts/3Q2026.csv (download page https://www.iftach.org/taxmatrix4/TaxDownload.php), read on 2026-09-29
MPG to two decimals: IFTA Procedures Manual (effective January 2026), P720.350 "Average fuel consumption factor (to two decimal places)" — https://www.iftach.org/manuals/2026/PM/Procedures%20Manual%20-%2001-01-26.pdf, read on 2026-09-29
Whole units per jurisdiction: IFTA Procedures Manual (effective January 2026), P720.500 Required Information — https://www.iftach.org/manuals/2026/PM/Procedures%20Manual%20-%2001-01-26.pdf, read on 2026-09-29
Taxable gallons: Virginia DMV, RDT 121-I IFTA Quarterly Tax Return Instructions, Section 7 column D and Section 8 column E — https://www.dmv.virginia.gov/sites/default/files/forms/rdt121i.pdf, read on 2026-09-29
Surcharge: Virginia DMV, RDT 121-I IFTA Quarterly Tax Return Instructions, Surtax/Surcharge — https://www.dmv.virginia.gov/sites/default/files/forms/rdt121i.pdf, read on 2026-09-29
Tax-paid credit: IFTA Articles of Agreement (effective January 2026), R1000 Tax Paid Purchases and R1010 Retail Fuel Purchases — https://www.iftach.org/manuals/2026/AA/Articles%20of%20Agreement%20-%2001-01-26.pdf, read on 2026-09-29

Frequently asked questions

How do I calculate IFTA taxable gallons?: Divide the taxable miles in the jurisdiction by your fleet MPG for the quarter and round to a whole gallon. At 6.52 MPG, 1,000 taxable miles are 153 taxable gallons.
Why is my IFTA tax negative in some states?: Because you bought more tax-paid fuel there than you burned there. The net taxable gallons are negative and the line is a credit that offsets the tax owed to other states; a total credit is refunded or carried forward under your base jurisdiction's rules.
Do I include Oregon miles?: Yes: every mile in every jurisdiction goes into the total miles and the MPG. The matrix lists no diesel rate for Oregon this quarter, so the Oregon line carries no tax here.
Which MPG should I use?: One MPG per fuel type for the whole return: all miles divided by all gallons placed in the trucks, two decimals. With several trucks, add their miles and gallons first; the fleet MPG calculator does that.
Can I use this for gasoline trucks?: Yes: pick gasoline, gasohol or biodiesel. Propane, LNG, CNG, alcohol blends, electricity and hydrogen use gallon equivalents or other units each jurisdiction defines, so they are left to your base jurisdiction's return.

Guides

How to calculate IFTA tax, step by step (with a worked example)
Fleet MPG, taxable gallons per state, tax-paid credit, net gallons, rate and surcharge: the IFTA return worked through one sample quarter with 3Q2026 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.