How to calculate FSC
A fuel surcharge passes changes in diesel prices through to the rate. The formula most contracts use is short:
- FSC per mile = (current diesel price − base price) ÷ MPG
- FSC per load = FSC per mile × miles
The base price, sometimes called the peg, is the diesel price already covered by the linehaul rate. The MPG is a figure the parties agree on, not your truck's actual mileage. Both come from the contract or the rate con. If diesel falls below the base, the surcharge is zero, not negative.
A worked example
A dedicated dry van lane pays $1,500 linehaul for 600 miles, plus a fuel surcharge with a $1.25 base and 6 MPG. Diesel is at the U.S. average of $6.38.
- FSC per mile
- $0.855
- FSC this load
- $513
- Share of linehaul
- 34.2%
- Linehaul + FSC
- $2,013
At today's prices the surcharge adds over a third to the linehaul. That's why it matters so much whether a rate is all-in or pays fuel separately: an all-in spot rate has to cover all of that from the rate itself.
Now drop diesel to the year-ago average of $3.75 and the surcharge on the same load falls to about $250. Same lane, same truck, same base rate: the surcharge is doing the work of keeping the carrier whole as fuel moves.
Today's diesel price
The U.S. average on-highway diesel price was $6.38 a gallon in late September 2026, against $3.75 a year earlier.
Source: U.S. EIA, U.S. On-Highway No. 2 Diesel retail price, weekly average, late September 2026, October 2026
Source: U.S. EIA, U.S. On-Highway No. 2 Diesel retail price, weekly average, late September 2025, October 2026
A jump like that is exactly what fuel surcharges are for. Carriers on all-in rates set when diesel was cheaper feel it immediately; carriers on contracts with a surcharge are protected as long as the formula is fair. EIA publishes the weekly average every Monday, so check it before you price a load.
Reading your result
Compare the surcharge with what fuel actually costs you per mile: your real price divided by your real MPG. If your truck gets worse mileage than the contract figure, part of your fuel cost isn't covered, and the linehaul has to make up the gap. The table under the result shows how the surcharge moves as diesel goes up or down by ten cents.
On a spot load quoted all-in, there's no separate surcharge, so use the trip fuel cost calculator to see how much of the rate fuel will eat, and the rate per mile calculator to compare offers fairly.
Negotiating a fuel surcharge
On dedicated or contract freight, the surcharge terms are part of the deal, so look at them as closely as the base rate. A base price set too high, or an MPG set too high, quietly shrinks the surcharge every week. Ask which diesel average is used, which day of the week it's taken from, how often it updates, and whether the surcharge applies to loaded miles only or empty miles too. Run each version through the calculator; small changes in the base or MPG add up to real money over a year.
Common fuel surcharge mistakes
- Comparing an all-in spot rate with a contract rate plus surcharge as if they were the same thing.
- Using your own MPG in the formula instead of the contract's.
- Accepting an old base price on a new contract without asking.
- Forgetting that reefer unit fuel and idling at docks sit outside the formula.
Fuel surcharges by truck
The formula is the same for every truck, but the inputs differ. Heavier flatbed and tanker loads burn more fuel per mile than the contract MPG often assumes. 26 ft box trucks and hotshots usually get better mileage, so a contract written for tractor-trailers can overpay them. Reefers burn fuel the formula never sees, in the unit; estimate it with the reefer fuel burn calculator.
When we dispatch your truck, we check whether each offer is all-in or pays fuel separately, and how fuel is handled on long reefer waits, before the load reaches you. You see the full rate con before you say yes. Our fee is 5% for one truck with authority older than 6 months. See reefer dispatch.