How to Calculate IFTA, Step by Step (With a Worked Example)
IFTA math intimidates people because it involves every state you touched — but the calculation itself is three steps of arithmetic, repeated per state. Here’s the whole method, with numbers.
Step 1 — Compute your fleet MPG for the quarter
Total miles everywhere ÷ total gallons purchased everywhere. Say you ran 24,000 miles and bought 3,800 gallons: 24,000 ÷ 3,800 = 6.32 MPG. This single number drives everything else, which is why sloppy fuel records poison the whole return.
Step 2 — Taxable gallons per state
For each state: miles driven there ÷ your fleet MPG. If you ran 4,800 miles in Pennsylvania: 4,800 ÷ 6.32 = 759 taxable gallons. That’s the fuel you burned in Pennsylvania, regardless of where you bought it.
Step 3 — Net gallons and tax
Subtract the gallons you actually purchased in that state, then multiply by the state’s current rate (rates change quarterly — always use the published rate table for the quarter you’re filing).
Bought only 250 gallons in Pennsylvania? Net = 759 − 250 = 509 gallons. At a rate of, say, $0.74/gal, you owe Pennsylvania about $377. Bought 700 gallons in Ohio but only burned 500 there? That’s a 200-gallon credit at Ohio’s rate.
Step 4 — Sum every state
Add up the owed amounts and the credits across all jurisdictions. You file one return and settle one net number with your base state; the states sort the money out among themselves. Some quarters you’ll owe; if you fuel strategically in higher-tax states you drive through, you can genuinely come out with a refund.
Where people go wrong
Four mistakes cause most audit pain:
- Missing fuel receipts — purchases you can’t prove don’t count as tax-paid gallons, which inflates what you owe
- Estimated or “rounded” miles per state instead of actual route miles
- Forgetting deadhead — empty miles are taxable miles
- Using last quarter’s rate table — rates move every quarter
Automate the inputs, keep the output
Notice that every error above is a record-keeping error, not a math error. Tag each fuel stop by state when you buy it and log miles as you run them, and the calculation becomes mechanical — Load Cabin runs it continuously so the quarter-end “calculation” is just reading a number. Try the interactive version on our IFTA calculator page.
Load Cabin logs your loads, fuel, and inspections from the cab — IFTA, invoices, and cost per mile build themselves. 30 days free, no card.
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