A load pays $2,300, diesel has moved higher since the lane was priced, and the broker mentions a fuel surcharge. Is that surcharge calculated from the pump price you paid yesterday? From a weekly national average? From the miles on the rate confirmation? The answer depends on the agreement—not on a government-mandated rate.
This guide gives a reproducible example of one common per-mile diesel-price adjustment, explains how to check the fuel clause before invoicing, and shows why paid and unpaid mileage matter. It is written for U.S. owner-operators, dispatchers and small trucking companies reviewing load economics or negotiating a customer contract.
Open the free Fuel Surcharge Calculator to enter your own fuel reference, mileage and MPG assumptions. The calculator does not retrieve current diesel prices, does not issue an invoice, and does not determine your legal entitlement to payment.
Who decides the diesel fuel surcharge?
The U.S. Energy Information Administration (EIA) gathers and reports retail on-highway diesel fuel prices. As the agency explains on its diesel fuel surcharge guidance, it does not calculate or regulate carrier fuel surcharges. Transport companies and customers can choose their own methods.
Consequently, a formula that works for a contracted shipper may not apply to a brokered spot load. Before using any calculation, identify whether your contract or rate confirmation specifies:
- An index: national, regional or another published diesel series, or a specific supplier’s invoice price.
- A reference week or observation date: the prior Monday, the week of loading, a monthly average or another period.
- A base fuel price: the dollar-per-gallon threshold from which the price change is measured.
- A conversion factor: contract MPG, cents-per-mile schedule, percentage of linehaul or another negotiated mechanism.
- Eligible mileage: paid loaded miles, approved route miles, all miles or a fixed distance.
- Rounding, negative adjustments and floors: including whether a rate can fall below zero or uses step brackets.
- Billing and dispute provisions: which documents must support the invoice and how the charge is shown.
An EIA retail observation is market reference data, not a carrier’s actual fuel bill and not an automatically payable freight surcharge.
A simple per-mile fuel surcharge formula
For an agreement using a diesel-price difference divided by an agreed fuel economy factor, a simplified formula is:
Fuel price difference ($/gal) = current contracted diesel index − contract base diesel price.
Surcharge per eligible mile ($/mile) = max(0, fuel price difference) ÷ agreed MPG × adjustment percentage.
Estimated invoice surcharge ($) = surcharge per eligible mile × eligible miles.
The max(0, …) term represents a zero floor. It is included in the calculator because the example assumes a nonnegative surcharge; it is not a rule that all carriers or shippers follow. The adjustment percentage is an optional factor within this illustrative model and does not necessarily appear in an actual contract.
If your agreement uses a flat $0.18/mile surcharge, a bracketed schedule or a surcharge equal to a fraction of freight charges, calculate from that agreement rather than forcing the per-mile formula above.
Worked example: 800 paid miles plus 120 deadhead miles
Assume a carrier has agreed to a simplified contract clause with these illustrative terms. The prices are not presented as actual prices for October 2026.
| Item | Example input | Meaning |
|---|---|---|
| Diesel reference price | $4.00/gal | Manually supplied index value |
| Base diesel price | $3.25/gal | Contract threshold |
| Contract fuel economy | 6.5 MPG | Agreed divisor |
| Eligible loaded or billable distance | 800 miles | Miles paid at the surcharge rate |
| Deadhead / non-billable distance | 120 miles | Additional empty business miles |
| Adjustment percentage | 100% | Full per-mile price difference in this example |
Step 1 — Find the price difference. $4.00 − $3.25 = $0.75 per gallon.
Step 2 — Convert to a mileage rate. $0.75 ÷ 6.5 MPG = approximately $0.1153846 per eligible mile, or 11.54 cents. Do not round the 11.54 cents too early if your contract requires calculation from an unrounded rate.
Step 3 — Apply eligible distance. $0.1153846 × 800 eligible miles = about $92.31 of illustrative fuel surcharge.
Step 4 — Compare against the fuel-price change on the entire trip. Total distance is 920 miles including 120 deadhead miles. At the same 6.5 MPG assumption, the trip consumes about 141.54 gallons. The additional fuel-price expense compared with the $3.25 baseline is 141.54 × $0.75, or approximately $106.15.
Step 5 — Identify the unrecovered amount. The modeled surcharge of $92.31 offsets $106.15 of extra fuel expense. That leaves an approximately $13.85 shortfall attributable to the 120 unpaid miles. Actual spending will differ with route, idling, load, grade, weather, fuel cards and the gallons actually bought.
| Calculated result | Illustrative value |
|---|---|
| Fuel surcharge per eligible mile | $0.1154 |
| Fuel surcharge on 800 paid miles | $92.31 |
| Fuel-price change across all 920 miles | $106.15 |
| Remaining shortfall vs base fuel price | $13.85 |
These values measure a change from a chosen base price. They do not establish your total trip profit: a carrier can recover the fuel-price increase and still lose money on insurance, repairs, empty miles or financing.
Why deadhead creates a recovery gap
A shipper may pay the fuel surcharge only on specified route miles. But the tractor may travel additional empty miles to reach pickup, find parking, reposition after delivery or return to a viable lane.
Suppose the paid mileage remains 800 while deadhead rises from 120 to 220 miles. The calculated invoice surcharge stays the same at $92.31 if the contract still pays only 800 miles. However, the extra fuel-price expense is now based on 1,020 total miles and increases to approximately $117.69. The unrecovered increase becomes about $25.38.
This is why the Load Profitability Calculator treats deadhead as a business expense and not merely a routing note. It also explains why an apparently strong dollar-per-loaded-mile offer may underperform over total miles driven.
If the contract reimburses fuel on all eligible actual miles, the paid-mile assumption changes. Do not quietly add deadhead to an invoice if the agreed surcharge definition excludes it.
What if the agreement recovers only part of the diesel difference?
Some commercial terms cap fuel-price adjustments or apply a percentage. With the example above, a 50% adjustment would produce around $46.15 instead of $92.31 in surcharge revenue. The $106.15 fuel-price increase across the trip would remain the same. The resulting shortfall would be roughly $60.00.
This is not a legal or industry-standard rate recommendation. It is a sensitivity check: changing the recovery percentage, contract MPG factor or billable mileage can materially change how much price movement is passed through to the customer.
Also check whether the linehaul price itself was negotiated with higher diesel costs already included. Adding a surcharge may be inappropriate if the agreement expressly states an all-inclusive rate.
Which EIA diesel price should you use?
The EIA Gasoline and Diesel Fuel Update publishes weekly U.S. on-highway diesel price information. The EIA survey methodology describes a sample of retail diesel outlets and explains that its observations are weighted averages, not every truck’s actual purchase price.
If your contract says to use a certain EIA regional diesel series for the preceding week, use exactly that series and period. Do not use an unrelated national number because it is easier to find. The survey excludes Alaska and Hawaii from the contiguous-U.S. sample, and contract geography can matter.
For records, save the reporting week and URL alongside the contract language used to select it. If a broker uses an index from a different date, ask which clause supports that date before invoicing.
The calculator intentionally requires you to type the price: it does not display live diesel quotes and never pretends an example value is an EIA observation.
Why MPG can be different in a fuel clause and on the road
A carrier’s real MPG varies with the equipment, driving cycle and payload. Contracts sometimes assume a fixed MPG factor that may differ from the truck’s recent operating performance. Changing the agreed MPG factor changes a calculated per-mile adjustment even when the index price stays unchanged.
For example, a $0.75 price increase divided by 6.0 MPG equals 12.5 cents per mile, while the same price increase divided by 7.5 MPG equals 10 cents per mile. Across 800 eligible miles, those examples produce $100 and $80, respectively, before contract rounding.
For invoice purposes, use the agreed factor. For internal cost planning, separately record actual fuel purchases and operating MPG. Mixing a contract formula with a realized fuel expense model makes it difficult to reconcile the results.
How a fuel surcharge differs from a fuel card discount
A discount fuel card affects what you actually pay at participating stations. A fuel surcharge is a charge or price adjustment under the transportation agreement. One should not be automatically treated as the other.
A contracted diesel-index adjustment might remain unchanged even if you receive a better fuel-card price. Conversely, switching to a cheaper stop may require a detour that consumes some of the savings.
Read the separate guide to fuel cards, discounts and fees if you are comparing pump-price offers. Then feed your actual estimated per-mile cost into the Cost-per-Mile Calculator rather than assuming surcharge dollars equal profit.
Before accepting a brokered load: a practical checklist
Check the rate confirmation and relevant contract before dispatch:
- Locate the fuel clause. Confirm that fuel surcharge is payable in addition to linehaul rather than being included in the quoted amount.
- Record the reference series. Save the agreed EIA series, index week and base fuel level if a published index is used.
- Check billable miles. Determine whether the contract uses loaded, practical route, actual or another distance basis.
- Identify the calculation method. Is it cents per mile, a bracketed table, a flat dollar amount, a percentage or a different approach?
- Recalculate from the contract. Apply the agreed MPG, floor, rounding rules and observation date.
- Keep evidence. Save the rate confirmation, index observation and calculation with the invoice where the arrangement requires it.
- Test whole-trip economics. Add deadhead, fuel actually expected to be purchased, tolls, driver costs, financing and time exposure before accepting the load.
A broker can be obligated to pay an agreed fuel adjustment, but a calculator cannot establish that obligation without the contractual text. Disputes about fuel surcharge often begin with mismatched assumptions about dates, route mileage or whether the quoted rate was all-in.
Common calculation errors
Using current pump price without checking the index. A receipt from a particular station and a weekly EIA regional weighted average serve different purposes. Substitute a receipt only if the contract allows it.
Rounding cents per mile before multiplying. A displayed rate of $0.12 may differ noticeably from an underlying $0.1153846 when applied to hundreds or thousands of miles. Follow contractual precision and round the final amount as agreed.
Charging on all miles when only loaded miles are payable. The truck bears empty-mile fuel expense, but that does not mean the customer agreed to reimburse those miles.
Treating the fuel-price change as total fuel cost. The price difference from the base level is not the same as total gallons multiplied by today’s diesel price. The calculator shows both to keep the concepts separate.
Double-counting fuel in trip profitability. If your all-in cost per mile already includes diesel, do not add the full diesel spend a second time when estimating load profit. Reconcile the cost basis first.
Assuming a surcharge always rises with diesel. Some negotiated schedules use bracket thresholds, lags or caps. A simple formula may not reproduce those terms.
When this calculator is useful—and when it is not
Use the calculator to illustrate a per-mile diesel-index clause, compare the effect of deadhead, and create a CSV record of an estimate. It helps you ask better pricing questions before a load is booked.
Do not use it to claim reimbursement under a contract you have not checked, calculate IFTA liability, issue a tax invoice or substitute for full trip profit analysis. Nor should it be treated as an authoritative current diesel price feed.
If you need to decide whether to accept the load, combine the anticipated contractual surcharge with the linehaul rate and then use the Load Profitability Calculator. If you need to evaluate the business more broadly, review how to calculate your real cost per mile.
Next action: Calculate your estimated fuel surcharge using your own contract inputs, and compare the result against all trip miles before accepting the rate.
A contractual surcharge can offset diesel-price changes without solving the gap between buying fuel and receiving a customer payment. Forecast those weeks separately in the carrier cash runway calculator.
Fuel surcharge eligibility and business-mile exposure are different calculations. Our deadhead cost guide shows why empty positioning can reduce load profit even when a fuel adjustment is collected.
A card may change your purchase cost without changing the fuel surcharge specified by a freight contract. Evaluate purchasing economics separately with the Fuel Card Savings Calculator.