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Is your freight spend up from fuel or from rates?

By Noam Turecki · 27 October 2026

To see how much of a freight spend rise is fuel and how much is rate, split every freight bill into three lines: linehaul (the rate without fuel), fuel surcharge, and shipment count, plus an other charges column for anything else. One total can't tell you which one moved.

The September 2026 figures from Cass show why. According to Cass, as reported by TL linehaul rates up 10% in September, shipment counts remain positive - FreightWaves, freight spend rose 20.4% year over year while shipments rose 1.9%.

If you'd like those lines on one screen instead of a spreadsheet, Plymouth AI Lab builds logistics dashboards that show numbers such as cost per shipment, from the data in a firm's warehouse management system (WMS), transportation management system (TMS), accounting tool and spreadsheets.

Why a single freight total hides the cause

A total mixes three things that move separately: how many shipments you send, what carriers charge for the haul, and what diesel does to the bill. The same FreightWaves article, dated October 13, 2026, names all three as drivers behind the higher index: more shipments, higher freight rates and surging diesel prices.

Here are the year-over-year changes it reports for September 2026, all from the Cass report as relayed by the article.

Volume barely moved, the linehaul index moved a lot, and diesel moved more than either. Read as one total, the 20.4% hides that.

Track fuel surcharge separately from linehaul, using invoices you already hold

The freight bills you already pay hold everything required. Lay them out so each charge lands in its own column.

1. Make one row per freight bill.
2. Put the base rate in a linehaul column and the fuel surcharge in a fuel column. Put anything else in a third column called other charges.
3. Count shipments for each period.
4. Compare each column, year over year, against the shipment count.

Per the article, Cass builds its indexes from freight bills it pays, and its linehaul index tracks rates excluding fuel and accessorial surcharges. Your linehaul column follows that same idea.

Don't use Cass as a benchmark for your own lanes. The article says its shipments index covers all domestic transportation modes, with truckload and less-than-truckload shipments making up the bulk of the data. It also says the linehaul index is historically heavily weighted to contract rates but includes for-hire spot rates.

Check the fuel column against your contract, with the public diesel price as context

Test your fuel column against the surcharge table in your own contract, and keep the public diesel price beside it as context. The contract is the test because the EIA page How do I calculate diesel fuel surcharges? - Frequently Asked Questions (FAQs) - U.S. Energy Information Administration (EIA) says fuel surcharges are negotiated privately by shippers and transportation companies, and that each company may use its own method for calculating them.

It adds that many shippers, transportation companies and truckers use the weekly retail diesel price in their fuel pricing formulas. EIA itself does not calculate, assess or regulate diesel fuel surcharges.

That weekly price is the context. The U.S. Energy Information Administration (EIA) publishes a weekly Gasoline and Diesel Fuel Update - U.S. Energy Information Administration (EIA), with U.S. on-highway diesel prices in dollars per gallon, taxes included.

The release dated October 20, 2026 shows $6.276 per gallon on 10/19/26, against $2.656 a year earlier. That is more than double (6.276 against 2.656, calculated from EIA's table).

That page lists October 27, 2026 as its next release date, so a newer week may be out by the time you read this. $6.276 is the 10/19/26 reading.

So when a fuel charge on a bill doesn't match what the contract says, that's a question for the carrier, and you now have the rows to ask it with.

A worked example with the public September numbers

This example uses public Cass index data from September 2026. The article reports changes in Cass indexes, not dollar amounts, and no firm's invoices are involved.

Total spend rose 20.4% on 1.9% more shipments. Dividing 1.204 by 1.019 gives about 1.18, so cost per shipment rose about 18% year over year. That is an index calculation from the 20.4% and 1.9% figures.

Against that 18%, the linehaul index is up 10.1% and diesel is up 68%. The linehaul index excludes fuel and accessorial surcharges, while the spend index includes fuel, so the gap between 18% and 10.1% sits somewhere in fuel, other charges and mix.

The share of spend that is fuel is unknown in this example, since the sources do not give it. Your own fuel column gives it.

Don't combine the 68% and the EIA price into one figure either. The 68% is a September diesel number from the Cass report. The EIA figure is a single week, 10/19/26. They are different measures.

What the three lines will not tell you

The split shows where the money moved. The reason a carrier priced a lane the way it did sits outside those columns. If your volume is flat but your mix changed (lanes, modes, weight), cost per shipment can move for reasons outside fuel and rate.

The Cass linehaul index mixes contract and spot rates, so your contract lanes may not track it. Each company may use its own surcharge method, so check each fuel line against its own contract.

This week, pull the last three months of freight bills into one sheet with columns for linehaul, fuel surcharge, other charges and shipment count. Then compare each against the same months last year.

Sources

• freightwaves.com
• eia.gov/petroleum/gasdiesel
• eia.gov/tools/faqs/faq.php

Related service: Supply chain analytics and logistics dashboards, built from your own data

This post was researched and drafted by AI agents, then checked by a separate AI fact-checker and reviewer before publishing. Every source is linked above.