Idaho IFTA fuel tax rate
3rd Quarter 2026 diesel (“special fuel”) rate for Idaho.
How Idaho tax is figured
- 1. Fleet MPG for the quarter = total miles everywhere ÷ total gallons bought everywhere.
- 2. Taxable gallons in Idaho = miles run in Idaho ÷ fleet MPG.
- 3. Net gallons = taxable gallons − gallons you actually bought in Idaho.
- 4. Tax = net gallons × $0.3200.
Worked example
| Miles in Idaho | 4,000 |
| Fleet MPG (all jurisdictions) | 6.00 |
| Taxable gallons | 666.67 |
| Gallons purchased in Idaho | 300 |
| Net taxable gallons | 366.67 |
| Tax due (or credit) | $117.33 |
Common questions
Does the Idaho rate change every quarter?
It can. IFTA publishes a new tax-rate matrix each quarter, and jurisdictions adjust rates, surcharges and index-linked amounts on their own schedules. The rate above is from IFTA, Inc. Tax Rate Matrix (3Q2026), USD per gallon.
Do I file this return with Idaho?
No. You file one IFTA return with your base jurisdiction covering every state and province you ran in, and it distributes the money. FuelTaxDesk produces the worksheet you file from — you stay the filer of record.
What if I bought more fuel here than I burned?
Net gallons go negative and the line becomes a credit, which offsets tax owed in other jurisdictions on the same return.
Run your whole quarter free
Enter miles and gallons for every state you ran. No ELD, no GPS, no signup for the calculator.
Open the calculatorInformational only, not tax advice. Verify rates against your base jurisdiction and the official IFTA tax-rate matrix before filing.