IFTA calculation overview

Each quarter, carriers report total miles and fuel gallons, then calculate net tax due or credit for every jurisdiction on the return. The same core formula applies everywhere; only the mileage, gallons, and tax rates change by jurisdiction.

Required inputs

  • Total miles traveled in each jurisdiction
  • Total gallons purchased in each jurisdiction
  • Total fleet miles and total fleet gallons for the quarter
  • IFTA fuel tax rate per jurisdiction for the filing quarter

Missing any of these inputs makes the return inaccurate or incomplete.

Total miles

Summarize all commercial miles by jurisdiction for the quarter. Trip-level detail should support these totals if your base jurisdiction requests an audit.

Route-based mileage software can split miles at state lines automatically. See IFTA mileage tracking.

Total gallons

Add all taxable fuel gallons purchased during the quarter. Keep receipts that show date, location, and gallons so tax-paid gallons by jurisdiction are verifiable.

Fleet MPG

Fleet MPG is typically calculated as:

Fleet MPG = Total Miles ÷ Total Gallons

This average MPG is used to estimate taxable gallons consumed in each jurisdiction based on jurisdiction miles.

Tax-paid fuel

Tax-paid gallons are the fuel gallons purchased in a jurisdiction where fuel tax was paid at the point of sale. Those gallons offset the taxable gallons consumed in that same jurisdiction.

Tax due or credit

For each jurisdiction, the basic relationship is:

  1. Taxable gallons consumed = Jurisdiction miles ÷ Fleet MPG
  2. Net taxable gallons = Taxable gallons consumed − Tax-paid gallons purchased
  3. Tax due or credit = Net taxable gallons × Jurisdiction tax rate

Positive results are tax owed; negative results may create a credit depending on jurisdiction rules.

Example calculation

Suppose for one jurisdiction in a quarter:

  • Jurisdiction miles: 10,000
  • Fleet MPG: 6.5
  • Tax-paid gallons purchased in jurisdiction: 1,200
  • Tax rate: $0.40 per gallon

Taxable gallons consumed = 10,000 ÷ 6.5 = 1,538.46 gallons

Net taxable gallons = 1,538.46 − 1,200 = 338.46 gallons

Tax due = 338.46 × $0.40 = $135.38

Note: Real returns include every jurisdiction on your license and may involve rounding rules set by your base jurisdiction.

How software simplifies this

Spreadsheets work for very small fleets, but errors add up quickly across many jurisdictions. IFTA software organizes trips, fuel, and jurisdiction totals so quarterly reports are faster and easier to verify.

IFTAfy generates quarterly reports from trip and fuel records. Compare options on our best IFTA apps page or review the full IFTA reporting guide.