Worked example
If 45 litres is 5p/litre cheaper, you save £2.25 at the pump. But an 8-mile detour in a 40 MPG car uses roughly 0.91 litres, so a meaningful chunk of the apparent saving disappears.
Frequently asked questions
What should I enter for extra distance?
Only the miles you would not otherwise drive. If the cheaper station is directly on your normal route, enter zero.
Does this include the value of my time?
No. If the detour takes significant extra time, the true benefit may be even smaller.
Which fuel price is used for the detour?
The calculator uses your usual local price as a conservative estimate of the fuel burned getting there and back.