When diesel prices rise, hauliers send surcharges. Many are fair. Some apply the full diesel increase to the whole freight bill, which overstates the real cost several times over.
With EU diesel at a record €2.23 per litre in September 2026, these letters are landing on many buyers' desks. Here is how to check one in a few minutes.
Why only part of the bill should move
Fuel is only one part of what a haulier pays. Driver wages, vehicles, insurance, tolls and margin do not change when diesel moves. A fair surcharge applies the diesel change to the fuel share of the freight cost, and to nothing else.
The calculation
In this example, a fair surcharge is about €114 per load, or +11.4% on freight. A request for +38% on the whole bill would cost you more than three times as much.
The figures are illustrative. The fuel share has to come from the supplier, and the diesel change from a published index such as the European Commission's Weekly Oil Bulletin.
Ideally, the fuel share, the index and the base date are agreed in the transport contract before prices move, not negotiated after a surcharge arrives. If your contract already defines a different method, that method applies.
What to ask the supplier for
- The fuel share of their freight cost, by lane
- The diesel index they use, and the base date and value
- The current index value the surcharge is calculated from
- Whether the rate is contract or spot
- An automatic downward adjustment when diesel falls
A surcharge that comes with these answers is easy to agree. One that doesn't is a starting point for a conversation, not an invoice.
The same logic works elsewhere
Energy and packaging claims follow the same rule: apply the change only to the part of the cost that is actually exposed. A gas price increase matters for the unhedged energy share of a product, and a resin increase for the grams of plastic in each pack.