How to Calculate a Fuel Surcharge: Per Mile and Percentage Methods
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To calculate a fuel surcharge per mile, subtract the base fuel price from the current diesel price, then divide by the truck's miles per gallon. Multiply that figure by the miles on the load to get the dollar amount. Percentage contracts work differently: the price gap sets a percentage from a table, and that percentage applies to the freight charge.
This guide shows both formulas with real numbers, and how much the contract's base price changes the result. You can check your own figures with our free fuel surcharge calculator.
What is the fuel surcharge formula?
The per mile formula is: (current fuel price minus base price) divided by miles per gallon. The percentage formula is: (current price minus base price) divided by the step size, rounded down, times the percentage per step.
| Method | Formula | Applied to | Common in |
|---|---|---|---|
| Per mile | (Current minus Base) ÷ MPG | Miles on the load | Truckload |
| Percentage | Whole steps × % per step | Freight charge | LTL and many parcel or carrier tariffs |
If diesel is below the base price, the surcharge is zero, not a discount, unless your contract says otherwise. There is no single legal formula. The numbers that count are the ones written in your rate agreement.
Where do you find the current diesel price?
Most US programs use the weekly on-highway diesel average published by the U.S. Energy Information Administration. You can read it on the EIA Gasoline and Diesel Fuel Update page, which also breaks the price down by region.
The US average was $6.352 per gallon on October 26, 2026, and the examples below use $6.35. Check which figure your contract names, national or regional, and which day of the week it takes effect. The EIA also has a short explainer on how diesel fuel surcharges work.
How do you calculate a fuel surcharge per mile?
Follow these four steps, using a $3.00 base price, a truck rated at 6.5 MPG and a 620 mile load.
- Find the price gap: $6.35 minus $3.00 = $3.35.
- Divide by MPG: $3.35 ÷ 6.5 = $0.515 per mile.
- Round as your contract says. Here, $0.52 per mile.
- Multiply by miles: $0.515 × 620 = $319.54 before rounding the rate.
Note that rounding matters on long hauls. At the rounded $0.52 rate, the same load comes to $322.40, a difference of about $3 on one trip. Agree on when to round, and on whether empty miles count.
How do you calculate a percentage fuel surcharge?
Count how many full price steps sit above the base, then multiply by the percentage for each step. Partial steps do not count until the price crosses the next one.
Take a contract with a $4.00 base, a $0.06 step, 1 percent per step and a $1,800 freight charge:
- Price gap: $6.35 minus $4.00 = $2.35.
- Whole steps: $2.35 ÷ $0.06 = 39.17, which rounds down to 39.
- Surcharge rate: 39 × 1% = 39%.
- Dollar amount: $1,800 × 39% = $702.
The total bill comes to $2,502. Some tables also add a starting percentage on top of the steps. Our calculator has a field for that, along with the step size and percentage per step.
How much do the base price and MPG change the result?
The base price is the biggest number in the deal, and MPG comes next. A small change in either can move the surcharge more than a week of diesel price swings.
This table uses a $6.35 diesel price and 620 miles:
| Base price | MPG | Per mile | On 620 miles |
|---|---|---|---|
| $1.25 | 6.5 | $0.785 | $486.46 |
| $3.00 | 5.5 | $0.609 | $377.64 |
| $3.00 | 6.0 | $0.558 | $346.17 |
| $3.00 | 6.5 | $0.515 | $319.54 |
| $3.00 | 7.0 | $0.479 | $296.71 |
| $4.00 | 6.5 | $0.362 | $224.15 |
A low base price is not automatically better or worse. An older contract may pair a low base with a lower line haul rate, so the surcharge carries more of the fuel cost. Compare all in rates, not surcharges alone. A landed cost calculator helps when freight is one part of a larger shipment cost.
How do you calculate a fuel surcharge in Canada or in litres?
Keep the units the same throughout. For metric contracts, multiply the price gap per litre by the truck's litres per 100 km, then divide by 100 to get a surcharge per kilometre.
For example, with fuel at $1.90 per litre, a $1.50 base and a truck using 35 L per 100 km:
- Price gap: $1.90 minus $1.50 = $0.40 per litre.
- Per km: $0.40 × 35 ÷ 100 = $0.14.
- On 1,000 km: $140.
These figures are for illustration only. One US gallon is about 3.785 litres, so convert before you compare a US gallon price with a Canadian litre price, and remember that the currencies differ too. Use the price index your contract names.
What should a fuel surcharge clause include?
A clear clause stops most billing disputes before they start. Put these terms in your agreement or on the rate confirmation:
- Index: the exact source, such as the EIA US average or a named region
- Timing: which weekly price applies and the day it takes effect
- Base price: the peg, written to the cent
- Method: per mile with the MPG, or a percentage table with its steps
- Which miles: loaded only, or all miles
- What it applies to: line haul only, or accessorial charges too
- Rounding: how many decimals, and at which step
Fuel is only one part of a freight bill. To price the rest of the load, try the freight density calculator and the dimensional weight calculator. You can also add the final figure to your bill of lading paperwork where your process calls for it.
Our calculator gives estimates to help you plan and check invoices. It is not legal or financial advice, and your contract decides the final amount. Run your numbers now.
Frequently asked questions
What is the formula for a fuel surcharge?
Per mile, it is (current fuel price minus base price) divided by miles per gallon. For a percentage table, divide the price gap by the step size, round down, and multiply by the percentage per step.
What is a typical base fuel price?
It depends on the contract. Older tables often use about $1.20 to $1.25 a gallon, and newer ones use a price closer to current diesel. Always use the figure in your agreement.
Where does the diesel price come from?
Most US programs use the weekly on-highway diesel average from the U.S. Energy Information Administration. Your contract should name the exact series, either national or regional.
What MPG should I use?
Use the MPG written in your contract. Many per mile programs assume about 6 to 6.5 MPG for a truck, but a lower figure raises the surcharge, so both sides should agree on it.
Can a fuel surcharge be negative?
Normally no. When the current price is below the base price, the surcharge is zero. A contract can set different terms, so check yours if prices fall.