Enter the price at two petrol stations to see how much you save per fill-up, in a month and over a year.
Is the detour worth it?
Station B saves you this much per month based on 2 fill-ups per month.
Litres per fill-up multiplied by the price per litre gives each station's cost per visit. The saving is the difference between those two costs. Multiply the saving per fill-up by how often you fill up each month to get your monthly saving, then multiply by twelve for the annual figure.
This shows the direct fuel saving from choosing the cheaper station for the litres you enter.
Assumptions
- The saving is based on the litres entered per fill-up, not a full tank from empty. Adjust the litres field to match how much you typically put in.
- Fuel prices change frequently. The defaults are approximate figures for early 2026.
The breakeven distance shows the point where the fuel used for the detour wipes out the saving from the cheaper station.
Example: if you save £2.00 on a fill-up and the extra driving costs about 16p per mile for a round trip, you can drive roughly 12.5 miles in total before the saving is used up. That works out to about 6.2 miles (£1.00) each way.
If the detour is shorter than that, you still save money on fuel. If it is longer, the extra driving costs more than the saving. Even when the detour is within the breakeven distance, it is still worth weighing the money saved against the extra time the trip takes.
- How many litres does a typical car tank hold?
- Most family cars in the UK hold between 45 and 65 litres. Smaller city cars are typically 35 to 45 litres, and larger SUVs or MPVs can be 70 litres or more. The litres per fill-up field defaults to 50, which is a reasonable example for a mid-size family car filling most of the tank. Adjust it to match how much you actually put in each visit.
- Does this work for diesel?
- The calculator works for diesel too because it uses the price and litres you enter. Enter the diesel pump price at each station and the litres you put in per visit, and the saving calculation is identical.
- How do I find my car's MPG?
- Your car's official MPG figure is in the handbook or on the manufacturer's website, but real-world efficiency is usually lower. The most accurate method is to fill up fully, reset the trip computer, drive normally until the next fill-up, then divide the miles driven by the litres used multiplied by 0.2200 (to convert to gallons). Many modern trip computers display a live or average MPG figure directly. For the MPG field in this calculator, use a realistic figure from your own driving rather than the official test number.
- How do I know how many times I fill up a month?
- Look back through your bank or fuel card statements to count fill-ups over the last two or three months, then average them. If you commute a set number of miles each week, you can estimate by dividing your weekly mileage by your car's range from a full tank, then multiplying by four. The default of two fill-ups per month suits a typical commuter covering around 800 miles a month.
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