Worked example
Diesel at $3.90 a gallon against a $1.20 base, a truck getting 6.5 miles per gallon, on a 500 mile run.
- Price above base: $3.90 − $1.20 = $2.70 per gallon.
- Spread over the miles a gallon buys: $2.70 ÷ 6.5 = $0.4154 per mile.
- Across the trip: $0.4154 × 500 = $207.69.
At a $2.50 linehaul rate that surcharge is about 16.6% of the line rate, which is roughly where the market has sat when diesel is near $3.90.
The formula
Gap = current diesel − base diesel, floored at 0 Per mile = gap ÷ truck MPG Per trip = per mile × miles % of line = per mile ÷ linehaul rate
The base price is not a market figure. It is the diesel price already assumed inside your linehaul rate, set by your contract or the carrier tariff, and it is usually a historic number in the $1.20 to $1.25 range.
Why MPG matters more than you expect
The surcharge divides the price gap by fuel economy, so a more efficient truck earns less surcharge on the same lane. At 6.5 MPG a $2.70 gap is 41.5 cents a mile; at 8.0 MPG the same gap is 33.8 cents.
That is a real consideration when you negotiate. If your fleet runs better than the MPG in the tariff table, a per-mile surcharge paid off the table rewards you. If it runs worse, the surcharge will not cover your actual fuel cost and the shortfall comes out of the linehaul.
Per mile or per cent
Truckload and LTL surcharge differently, and mixing the two up is how quotes go wrong.
Truckload normally uses the per-mile calculation on this page: a price gap divided by fuel economy, multiplied by loaded miles. It is transparent, it is easy to audit, and it tracks the actual cost of the fuel burned.
LTL normally applies a percentage of the linehaul charge instead, read off a published table that steps with the weekly diesel average. That percentage has run anywhere from the low twenties to over forty per cent in recent years, depending on the carrier and the diesel price. It bears no direct relationship to the fuel your particular shipment consumes, because an LTL trailer is carrying twenty other shipments at the same time.
When you compare carriers, compare the all-in rate. A low linehaul with an aggressive fuel table routinely costs more than a higher linehaul with a modest one, and the headline number is the one designed to be compared.
Common mistakes
- Using a national average when your lane is regional. The EIA publishes regional diesel prices weekly, and California in particular runs far above the national number.
- Guessing the base price. It is in the contract. Guessing it low inflates the surcharge and the customer will notice.
- Applying the surcharge to deadhead miles. Most tariffs surcharge loaded miles only unless the contract says otherwise.
- Expecting a credit below base. Almost every tariff floors at zero rather than paying back when diesel is cheap.
- Confusing a per-mile surcharge with a percentage one. LTL usually surcharges as a percentage of linehaul; truckload usually does it per mile. They are not interchangeable.
FAQ
How is a fuel surcharge calculated?
Subtract a base diesel price from the current price, then divide by the truck MPG. That gives the extra fuel cost per mile, which you multiply by the trip distance.
What base price should I use?
Whatever your contract or tariff specifies. It is the diesel price already built into the linehaul rate, so surcharge only applies above it. Older tariffs often sit around $1.20 to $1.25.
What if diesel is below the base price?
There is no surcharge. Most tariffs floor at zero rather than giving a credit back, which is how this calculator behaves.
Where do I find the current diesel price?
The US Energy Information Administration publishes a national and regional on-highway diesel average every Monday, and most carrier fuel tables key off it.
Why does MPG matter so much?
Because the surcharge is spread over the miles a gallon buys. At 6.5 MPG a $2.70 price gap costs about 41.5 cents a mile; at 8 MPG the same gap costs about 33.8 cents.
Rules last checked: Sep 24, 2026
Estimate only. Confirm with your carrier before booking.