So I've been fueling in Virginia where it's cheapest. I run minimal miles in PA despite living there.
I have been getting hit for about $100 every quarter because of PA. One or two fill ups more than offsets that $100.
So I probably know how it works now.
A very simple way to look at it, using fake numbers to make it easy.
Virginia:
Fuel Costs $3.00/Gallon
Fuel Tax on that fuel is $0.25/Gallon
$3.00-$0.25=$2.75 Net Cost
Pennsylvania:
Fuel Costs $3.00/Gallon
Fuel Tax on that fuel is $0.50/Gallon
$3.00-$0.50= $2.50 Net cost.
Smartest place to buy fuel is Pennsylvania with these numbers, you are saving $0.25/Gallon on fuel.
IFTA costs:
You average 5 miles/Gallon on fuel because you are a super trucker.
You drive 100 miles in each state, you used a total of 40 gallons of fuel or this ifta quarter for the 200 miles.
20 Gallons of fuel used in Virginia = you owe Virginia $5.00
20 Gallons of fuel used in Pennsylvania = you own Pennsylvania $10.00
Total IFTA bill is $15.00
Scenarios
You bought all fuel in Virginia:
$3.00 x 40 = $120
Taxes paid at the pump = $10
In this scenario, you are $10.00 short on paying IFTA, so you have to pay an additional $5.00.
$120 + $5 = $125 in total fuel and IFTA expenses.
or
You bought all fuel in Pennsylvania
$3.00 x 40 = 120
Taxes paid at the pump = $20
In this scenario, You over paid in IFTA by $5.00, so you either get $5.00 back, or a credit, depending on how you IFTA system works.
$120 - $5 (credit or refund) = $115 in total fuel and IFTA expenses.
Buying fuel in Pennsylvania saved you $10
Buying your fuel at the cheapest net price (with fuel tax removed from the cost) is always the best way to purchase fuel. This is true in every possible scenario, every time. It doesn't matter where you run the most miles, as this has zero to do with the equation.
Greencastle PA, fuel cost for me is $4.003, minus fuel tax it is $3.21 ($0.78.5/Gallon fuel tax)
Raphine VA, fuel cost for me is $3.569, minus fuel tax it is $3.261 ($0.30.8/Gallon fuel tax)
Best place to buy fuel out of those two options would be Greencastle, PA (same miles as above, running 150 in Virgina, 50 in PA)
PA
$4.003 x 40 = $160.12
Fuel Tax paid at the pump = $31.40
VA
$3.569 x 40 = $142.76
Fuel Tax paid at the pump = $12.32
You suck at driving, so you still average 5 mpg, LOL.
50 miles in PA = 10 gallons of fuel used = IFTA tax bill of $7.85
150 miles in VA = 30 gallons of fuel used = IFTA tax bill of $9.24
Total IFTA costs = $17.09
Pennsylvania ($14.31 Tax Refund or Credit)
$160.12 - $14.31 = $145.81 Total fuel and IFTA costs
Virginia (Additional $4.77 owed to IFTA)
$142.76 + $.4.77 = $147.53 Total fuel and IFTA costs
$147.53 - $145.81 = $1.72 saved by buying all of your fuel in Pennsylvania, even with a pump price that is $.434/Gallon higher than Virginia
For anyone trying to get their head around IFTA, the scenario comes out the same every time, all the time. Cheapest net fuel price always results in the lowest cost of operation. Pick any fuel locations and do the math.
The hard part comes when you are driving all over the country and not always knowing where you are going to be in the next few days, therefore not always knowing where you are going to be able to buy the cheapest net price fuel.
When you are operating in a specific area, simply find the fuel locations that provide the cheapest net fuel costs and fill up there all the time.
Often times, the cheapest net fuel costs will be found near state lines where the stations with higher fuel taxes are trying to compete with lower fuel tax stations near them in the next state.