Glossary
Detour Cost
Direct Answer / TL;DR
What is Detour Cost?
The fuel cost of driving to and from a cheaper petrol station. Detour cost is subtracted from the gross saving to calculate the true net saving. It depends on your car's MPG, the current fuel price, and the distance to the station.
Why does it matter for UK drivers?
Detour cost is calculated using your vehicle's real-world MPG and the current fuel price at your local station (since that's what you're burning in your tank on the way there). The formula: detour cost (pence) = (distance in miles × 2 × price per litre × 4.546) ÷ MPG.
The ×2 factor accounts for the round trip — you have to drive there and back. If the cheap station is on your planned route, the detour distance (and therefore cost) is zero. WorthThePump calculates the straight-line distance from your location to each station as a proxy for detour distance.
Detour cost varies significantly by vehicle type. In a Toyota Prius averaging 55 MPG, driving 3 miles to the cheap station and back costs about 72p at 145p/L. In a Ford Transit van averaging 30 MPG, the same trip costs £1.32. The van needs the cheap station to be much closer — or offer a much bigger price difference — to make the trip worthwhile.
For high-mileage drivers, the detour cost is proportionally less important. A courier who covers 300 miles per day knows their running cost to the penny, and a 2p/L saving on a 70-litre fill (£1.40 gross) is worth a 1-mile detour at most. Planning fuel stops around price differences makes real sense at that scale.
Detour cost is one of the three core inputs in WorthThePump's calculation — alongside the fill volume and the per-litre price difference. All three interact: a higher fill volume makes the gross saving bigger and can justify a longer detour; a lower-MPG car makes the detour cost higher and shrinks the worthwhile range.
Related terms
Further reading
Now you know what Detour Cost means —
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