Calculate your quarterly IFTA fuel tax by state from miles, gallons, and fleet MPG. Get net tax owed or credit per jurisdiction, plus KY/VA surcharges.
IFTA Fuel Tax Formula
IFTA fuel tax is worked out in four steps, repeated for every jurisdiction you traveled in during the quarter.
Fleet MPG = Total Miles / Total Gallons Purchased
Taxable Gallons = Jurisdiction Miles / Fleet MPG
Net Taxable Gallons = Taxable Gallons - Tax-Paid Gallons
Tax Due = Net Taxable Gallons * Tax Rate
Kentucky and Virginia add a surcharge on top of the base tax:
Surcharge = Taxable Gallons * Surcharge Rate
The variables are:
- Total Miles: every mile driven across all IFTA jurisdictions during the quarter.
- Total Gallons Purchased: all tax-paid fuel bought across every jurisdiction that quarter.
- Fleet MPG: your average miles per gallon for the quarter, applied to every jurisdiction.
- Jurisdiction Miles: miles driven in one state or province.
- Taxable Gallons: the fuel IFTA treats as burned in that jurisdiction, based on miles and MPG.
- Tax-Paid Gallons: fuel you bought, and paid tax on at the pump, inside that jurisdiction.
- Net Taxable Gallons: taxable gallons minus tax-paid gallons; a negative value is a credit.
- Tax Rate: that jurisdiction's fuel tax per gallon for the quarter.
- Surcharge Rate: the extra per-gallon charge that Kentucky and Virginia apply.
The calculator runs this math in three modes. Quarterly IFTA tax takes a row for each jurisdiction, builds fleet MPG from your combined totals, then returns net gallons, base tax, any surcharge, and a line total for each one, all summed into the amount you owe or the credit you are due. Tax for one jurisdiction runs the same steps for a single state when you already know your fleet MPG. Fleet MPG only divides total miles by total gallons so you can find the MPG figure the rest of the return depends on.
IFTA Diesel Rates and Surcharge Jurisdictions
Rates change every quarter, so confirm the current figure for your filing quarter on the official IFTA rate matrix at iftach.org. The values below are representative of recent quarters and show how wide the spread between jurisdictions can be.
| Jurisdiction | Diesel rate ($/gal) | Level |
|---|---|---|
| California | 0.971 | Highest |
| Pennsylvania | 0.741 | High |
| Illinois | 0.738 | High |
| Indiana | 0.630 | High |
| Washington | 0.584 | High |
| Texas | 0.200 | Low |
| Oklahoma | 0.190 | Low |
| Mississippi | 0.180 | Low |
| Hawaii | 0.160 | Low |
| Alaska | 0.088 | Lowest |
Two jurisdictions add a surcharge that many simple IFTA calculators skip. The surcharge is billed on every gallon you burned there, meaning your taxable gallons, and unlike the base tax you cannot offset it with fuel bought at the pump. Indiana levied a motor carrier surcharge in the past but has since folded it into its base rate.
| Jurisdiction | Surcharge charged on | Pump credit allowed | Recent surcharge |
|---|---|---|---|
| Kentucky | Taxable (burned) gallons | No | about $0.10/gal |
| Virginia | Taxable (burned) gallons | No | about $0.14/gal |
Surcharge rates move quarterly, so check the current amount before you file. Use the surcharge fields in the calculator to add these lines to your total.
Example IFTA Fuel Tax Calculations
Example 1: One state, tax owed
You drove 10,000 miles in Texas during the quarter and your fleet MPG is 6.0. You bought 1,200 gallons of fuel in Texas, and the Texas rate is $0.20 per gallon.
- Taxable gallons: 10,000 / 6.0 = 1,666.67
- Net taxable gallons: 1,666.67 - 1,200 = 466.67
- Tax due: 466.67 x $0.20 = $93.33
You owe Texas $93.33 because you burned more fuel driving there than you bought there.
Example 2: A surcharge state
You drove 5,000 miles in Kentucky at a fleet MPG of 6.0 and bought no fuel in the state. The base rate is $0.22 per gallon and the surcharge is $0.105 per gallon.
- Taxable gallons: 5,000 / 6.0 = 833.33
- Base tax: 833.33 x $0.22 = $183.33
- Surcharge: 833.33 x $0.105 = $87.50
- Total owed: $183.33 + $87.50 = $270.83
The surcharge is figured on all 833.33 taxable gallons, not on net gallons, and buying fuel in Kentucky would not reduce it.
Frequently Asked Questions
How do I calculate IFTA fuel tax?
Divide your total miles by your total gallons purchased to get fleet MPG. For each jurisdiction, divide the miles you drove there by that MPG to get taxable gallons, subtract the tax-paid gallons you bought in that jurisdiction, and multiply the result by the jurisdiction rate. A positive number is tax owed and a negative number is a credit. Add every jurisdiction together for your net tax due or refund for the quarter.
How are the Kentucky and Virginia surcharges calculated?
The surcharge rate is multiplied by your taxable gallons, which is the fuel you burned based on miles and MPG, not by your net gallons. Because the surcharge is not collected at the pump, you cannot claim a credit for fuel you bought in those states against it, so the surcharge is always an amount owed. It is reported on a separate line from the base tax.
Do I owe IFTA tax in a state where I bought no fuel?
Yes. IFTA tax follows the miles you drive, not where you fuel up. If you drove miles in a jurisdiction but bought no fuel there, all of your taxable gallons in that jurisdiction are owed, offset only by credits from fuel you paid tax on elsewhere.
