How to File IFTA: Quarterly Walkthrough
IFTA redistributes fuel tax you already paid at the pump to the states where you actually drove. Four steps, one deadline per quarter — and three traps that cost penalties. The Q3 2026 return (Jul–Sep) is due October 31, 2026.
When is IFTA due?
File with your base state by the last day of the month after each quarter ends:
| Quarter | Months | Due |
|---|---|---|
| Q1 | Jan–Mar | April 30 |
| Q2 | Apr–Jun | July 31 |
| Q3 | Jul–Sep | October 31 |
| Q4 | Oct–Dec | January 31 |
Late filing costs $50 or 10% of liability, whichever is greater, plus monthly interest — and you must file even for zero-mile quarters. Calendar all four now.
How do you file an IFTA return?
1) Gather miles and gallons by state. ELD mileage logs plus every fuel receipt, sorted by jurisdiction. Reconstruct from card statements if receipts are missing — but expect the worst MPG assumption on audit.
2) Compute fleet MPG. Total quarter miles ÷ total quarter gallons. Not the dashboard display, not one good tank — the quarter's real average, typically 4–8 MPG for diesel.
3) Compute each state's owed or credit. Taxable gallons = state miles ÷ fleet MPG. Balance = taxable − gallons bought there. Tax = balance × that state's rate. Bought more than you burned there? That's a credit offsetting other states.
4) File and pay (or claim credit). Enter the per-state numbers at your base-state portal. The IFTA calculator does steps 2–3 and exports a CSV audit trail — copy the rows straight into the filing.
Which states add IFTA surcharges?
Kentucky adds 10.5¢ and Virginia 14.3¢ per diesel gallon burned there — assessed on taxable gallons, so they are always owed and never generate credits. Indiana folds its surcharge into the base rate (no separate line). Oregon uses weight-mile tax instead of fuel tax: report the miles, IFTA due is $0, file weight-mile separately. Reefer-unit fuel is generally not IFTA-taxable — track it apart from propulsion fuel.
What does a worked IFTA quarter look like?
A solo truck runs 30,000 miles on 4,600 gallons in Q3: fleet MPG = 30,000 ÷ 4,600 = 6.52. Split by state:
| State | Miles | Taxable gal | Bought gal | Balance | Rate | Owed / (credit) |
|---|---|---|---|---|---|---|
| TX | 12,000 | 1,840 | 2,100 | −260 | $0.20 | ($52) |
| CA | 10,000 | 1,534 | 1,200 | +334 | $0.979 | $327 |
| AZ | 8,000 | 1,227 | 1,300 | −73 | $0.26 | ($19) |
| Net Q3 | 30,000 | $256 owed |
Texas and Arizona over-buys become credits; California under-buy dominates the bill. That is the whole game: fuel where the tax is high only when the price still wins — the credit math never beats cheap fuel. Run your own quarter in the IFTA calculator and export the CSV before you touch the state portal.
How do you survive an IFTA audit?
Auditors ask for three things: miles by state, fuel by state, and the system that produced both. Keep all three for 4 years. 1) Miles: ELD GPS logs by jurisdiction, every quarter, unedited — odometer jumps without trip records are the classic failure. 2) Fuel: every receipt with date, state, gallons, and vehicle number; card statements alone are weak without receipts. 3) Separation: reefer fuel logged apart from propulsion fuel, personal miles flagged, bulk-fuel withdrawals allocated by trip. Reconcile monthly — 15 minutes against your cost per mile fuel line — so quarter-end is copy-paste and audit day is a file handoff, not archaeology.
The 3 mistakes that cost money
1) Filing with stale rates — states adjust quarterly; always confirm the current matrix (or iftach.org) before filing. 2) Mixing reefer fuel into propulsion gallons — it inflates gallons, distorts MPG, and misstates every state. 3) Skipping zero-mile quarters — still required, still penalized. Reconcile fuel monthly against your cost per mile numbers so quarter-end is copy-paste.
Last reviewed October 2026. Rates: Q3 2026 IFTA matrix for the return due Oct 31; provisional Q4 2026 rates (US diesel unchanged from Q3) now in the calculator for the current quarter. Estimates only, not tax advice — verify with your base state before filing. Filed late? Estimate the damage with the IFTA penalty calculator.
IFTA filing FAQ
When is my IFTA return due?
Q1 Apr 30, Q2 Jul 31, Q3 Oct 31, Q4 Jan 31 with your base state. Late = $50 or 10% plus interest. File even with zero miles.
How is the tax calculated?
Fleet MPG = total miles ÷ total gallons. Per state: (state miles ÷ fleet MPG − gallons bought there) × state rate. Credits offset debts across states.
Which states add surcharges?
KY 10.5¢ and VA 14.3¢ per diesel gallon burned — always owed. IN folds it into the base rate. OR is weight-mile ($0 IFTA).
Is reefer fuel taxable?
Generally no. Track it separately and check base-state rules.
Should I buy fuel where taxes are low?
Buy where the pump price is low, not where the tax is low — IFTA redistributes the tax anyway. A $0.30 cheaper gallon beats any credit strategy.