How I Built a Free IFTA Calculator for Small Truck Fleets

Build-in-public note #1 · IftaDesk

I kept running into the same story in trucking forums: driver finishes a quarter, sits down to file, and discovers they can't read half their fuel receipts because thermal paper fades. That image, a stack of unreadable paper, became the starting point for this project.

The Problem Is Real, the Tooling Isn't

IFTA requires any commercial vehicle over 26,000 lbs (or three or more axles regardless of weight) to file a quarterly fuel-tax return. The math itself isn't hard: divide total miles by total gallons to get fleet MPG, then work state by state, compute gallons consumed per jurisdiction, subtract what you already paid in tax there, multiply the difference by that state's rate, and sum everything up. Credits from states where you over-purchased offset what you owe elsewhere.

Four steps. Repeatable math.

But the existing free tools mostly fall into one of two failure modes. First: a calculator that does the tax math but gives you a single lump number, no breakdown. Second: a mileage-tracking app that records where you drove but leaves the quarter-end arithmetic to you. The gap between those two things is where small fleets get hurt. Some operators pay a filing service around $75 per quarter just for the per-state split. That's $300 a year for arithmetic.

I wanted to build something that did the whole chain, free, no signup.

How the Calculator Actually Works

The core calculation is four operations chained together:

Fleet MPG              = Total Miles ÷ Total Gallons
State Gallons Consumed = State Miles ÷ Fleet MPG
Net Taxable Gallons    = State Gallons Consumed − Tax-Paid Gallons Purchased in State
State Tax Due          = Base Tax + applicable surcharge line items

A few states add surcharge layers with their own rules; the engine handles them as a separate line item, computed independently from the base tax. Miss that and your numbers will be wrong for every surcharge state every quarter.

The mileage tracker side works separately: the user logs miles and gallons per jurisdiction, the tool computes each state's share of total mileage live, then the totals feed into the tax calculation. I made these two things explicit tools, not folded together, because the record-keeping problem and the tax-math problem are different in character.

The rate table covers 48 US states and 10 Canadian provinces, sourced from the official Q3 2026 IFTA quarterly tax rate matrix. Tax rates change every quarter, so I built the rate data as a replaceable layer rather than hardcoding it into the calculation logic. Swapping in Q4 numbers shouldn't require touching the formula.

Two Things That Actually Bit Me

Oregon. Oregon appears in the official IFTA rate matrix as a blank cell (not zero, blank). Before I caught it, my engine was skipping Oregon rows entirely. That silently corrupted fleet MPG for any operator who drove through the Pacific Northwest. Oregon miles still count toward totals; the tax due is simply zero. Treating a blank cell as "skip this row" is wrong. It took me a while to realize the error was this quiet.

State-by-state credit flow. IFTA lets credits from states where you purchased more fuel than you consumed offset what you owe elsewhere. I thought I had the consolidation step right. Then I ran my output against official sample calculations and found the numbers didn't match for surcharge states — surcharges don't participate in the credit pool the same way base tax does. Getting the order of operations right took several iterations against reference outputs before the numbers lined up.

Where It Stands

The calculator and mileage tracker are live and free at iftadesk.com, no login, no paywall on the core math. Export features are planned for a paid tier, not live yet.

One thing worth knowing before you rely on any of this: the quarterly filing schedule is Q1 due April 30, Q2 due July 31, Q3 due October 31, Q4 due January 31. Late filings cost $50 or 10% of delinquent taxes, whichever is greater, plus 0.75% monthly interest. Even a zero-mileage quarter requires filing or the penalty clock starts. Most operators I've talked to didn't know the zero-mileage rule until they got caught by it.

There's more to do. ELD import (pulling per-state miles directly from a driver's telematics portal instead of manual entry) is on the roadmap but not live. The rate table will need updating each quarter. Fuel surcharge and rate-per-mile calculators are already up for operators who need the broader picture of what a load is actually worth.

If you run a small fleet and do your IFTA by hand, I'd be curious what part of it causes the most friction. The tool is there; what it gets right and wrong in real use is still something I'm figuring out.