If you have your own authority, chances are, you have to do the calculations yourself. Or maybe you are just curious about how it is done. In either case, there are five steps to follow to get an accurate number.

Step 1

Remember all those miles that you have been tracking from state line to state line? First, you will need to add those up for each state or Canadian province in which you have traveled during the previous quarter.

Step 2

Next, add up all the gallons of fuel you purchased in each state. You will want to keep a running total as well as a total for each state.

Step 3

Third, calculate your gallons used in each state. To do this, first calculate the overall fuel mileage for all miles traveled for the quarter to two decimal places:

	Total Miles Driven ÷ Total Gallons Purchased = Overall Fuel Mileage.
Next, you want to figure out how many gallons you used in each state:
	Total Miles Driven State A ÷ Overall Fuel Mileage = Gallons Used State A
Remember, you’ll want to do this for every state or province you travelled in that is a jurisdiction member of IFTA.

Step 4

Now you will calculate the fuel tax paid and the fuel tax owed by each state. To do this, you can use the chart in the rates table at http://iftach.org:

Calculate how much would be required for each state for the miles you drove there:

	Total Gallons Purchased State A x Fuel Tax Rate State A = Fuel Tax Required State A

Step 5

Finally, you calculate how much tax you actually owe:

	Fuel Tax Required State A – Fuel Tax Paid State A = Fuel Tax Owed State A

Again, you will need to do this for every state, and then you will need to add or subtract the results for each state or province to get one overall figure for the tax form.