Is DEF Reported in IFTA Fuel Tax Reports?

No. Diesel exhaust fluid (DEF) is not fuel, so it is not reported on your IFTA return and the gallons are not counted in your fuel total. You can still deduct what you spend on it as a business expense.

What is DEF?

DEF is a mixture of 32.5% urea and 67.5% deionized water. It is not a fuel additive and it does not go into the fuel tank. It is stored in its own tank on the truck, which has a blue cap and a smaller opening so a diesel nozzle will not fit. Because it is not used to propel the vehicle and is not added to any fuel, it is not subject to fuel tax in IFTA jurisdictions. Sales tax rules for DEF vary by state.

What is it used for?

Since 2010 new diesel engines have had to meet much lower nitrogen oxide (NOx) emission limits. Nearly all heavy-duty truck makers meet them with Selective Catalytic Reduction (SCR), which uses DEF. The fluid is sprayed into the exhaust stream, where it breaks NOx down into nitrogen and water. It does not go into the engine or the combustion process.

How much do I use and where do I buy it?

A truck typically uses roughly 2 to 3 gallons of DEF for every 100 gallons of diesel. DEF tanks on trucks commonly hold about 6 to 30 gallons. Most truck stops sell DEF at the pump or by the jug, and it is also sold in drums, totes and bulk. If you run out, the engine will limit your power and eventually the truck can be restricted until the tank is refilled.

Does it freeze?

DEF freezes at about 12 degrees Fahrenheit (minus 11 degrees Celsius). Freezing does not damage it, and the truck's DEF tank has a heater that thaws what the system needs soon after start-up.

What it means for your records

• Do not include DEF gallons in your IFTA fuel gallons. Fuel receipts that show both diesel and DEF should be split.
• Do record the DEF purchase as an expense, and keep the receipt.
• The Trip Sheet Central iPhone app reads a receipt that has both fuel and DEF on it and enters them separately, so only the fuel counts toward your IFTA report.

If you are unsure about your state's rules, check with your base jurisdiction. See also Frequently Asked Questions about IFTA.