Build a free IFTA calculator in a spreadsheet (no software subscription required)

You can calculate and file IFTA quarterly taxes correctly using nothing but a spreadsheet, the official IFTA Inc. rate matrix, and 15 minutes per quarter—no $30/month software, no complicated formulas.

You need exactly three inputs: miles per state, fuel purchased per state, and current tax rates

Most owner-ops overthink this. Your logbook or telematics system already has the mileage. Your fuel receipts or fuel card statement already has the gallons. The only new piece is pulling the current quarter's rates from IFTA Inc.'s tax matrix before you start.

Mileage by state comes from your start and end odometer readings or GPS data. Fuel by state comes from where you actually purchased it—the pump location, not where you consumed it. Those are two different things, and this is where most owner-ops first trip up.

Set up a spreadsheet with mileage and fuel columns

Create columns for Date, State, Miles Driven, Gallons Purchased, and Fuel Type (diesel, gasoline, etc.). Pull your logbook entries or telematics export and populate each row. Total the miles and gallons by state at the bottom. As of 2024, IFTA accepts distance data from telematics and GPS systems as long as it exports to XLS or CSV—not PDF screenshots, not handwritten notes.

Calculate fleet average MPG, then gallons consumed per state

Fleet Average MPG = Total Miles (all states combined) ÷ Total Gallons (all states combined)

Once you have that number, calculate gallons consumed in each state:

Gallons Consumed per State = Miles in That State ÷ Fleet Average MPG

This step matters because IFTA taxes are based on where fuel was used, not where it was bought. If you fill up 300 gallons in Texas but drive most of those miles in Oklahoma, Oklahoma gets credit for the consumption, not Texas.

Worked example: Q2 2026 IFTA calculation for a three-state run

Owner-operator runs 5,200 miles across Florida, Georgia, and South Carolina in Q2, purchasing 735 gallons total.

Fleet Average MPG: 5,200 ÷ 735 = 7.07 MPG

Now calculate gallons consumed in each state:

Next, calculate net taxable gallons (the difference between consumed and purchased):

Apply Q2 2026 IFTA Inc. rates. Using standard rates of $0.35/gallon for all three states:

In this scenario, you owe $0.11 for the quarter.

Surcharge states require a separate calculation line

If you have even one mile in Kentucky or Virginia, you owe a surcharge on all gallons consumed there, regardless of how much fuel you purchased. New York and New Mexico also impose surcharges. Calculate surcharge separately from base tax:

Surcharge Tax = Gallons Consumed × Surcharge Rate

Surcharges apply to total gallons consumed, not net taxable gallons. Add a separate row in your spreadsheet for surcharge states and calculate them independently from your base IFTA calculation.

Exclude reefer fuel and off-highway equipment from your totals

Do not include gallons that powered refrigeration units, PTO units, or auxiliary engines. IFTA only taxes fuel for the truck itself. If you use dyed diesel for reefer, that gallon gets zero entry on the IFTA form. Many owner-ops miss this and overpay or file an incorrect return; if you claim a reefer credit later, audits follow. Exclude it from the start.

File the official form by the quarterly deadline

Your spreadsheet summarizes the math. The official IFTA return (Form IFTA-500 or a state-specific form) is what you submit by the quarterly deadline: January 31st (Q4), April 30th (Q1), July 31st (Q2), October 31st (Q3). Most states let you file online and pay by ACH; a few still require paper. Keep your spreadsheet and all receipts for four years—audits ask for this.

When your fleet gets complicated—multiple trucks, Canadian miles, tax-paid versus exempt fuel tracking, trip permits—a $30/month tool saves hours per quarter and reduces audit risk. Until then, the spreadsheet works.