Why does the freight charge differ between two identical consignments booked a week apart?

Three of the four components are variable. The diesel surcharge adjusts monthly — a booking in a new calendar month may carry a different percentage if the European Commission Oil Bulletin moved to a new price band. Toll charges are route-fixed but change when national governments revise motorway rates. Accessorial fees vary if the delivery requirements differ — a tail-lift required on one booking but not the other changes the total. The base transport rate is the most stable element — it changes only if a contracted rate is renegotiated or a spot rate replaces it.