Guide
Manual spreadsheet fuel saving calculators require you to know your MPG and do the maths yourself
Manual spreadsheet fuel saving calculators require you to know your MPG and do the maths yourself. WorthThePump does it automatically using your number plate.
What is Manual Fuel Saving Calculators?
Several UK motoring sites and blogs publish manual fuel saving calculators — typically spreadsheet-style tools where you enter your MPG manually, the price difference per litre, and a detour distance. While these work in principle, they have a critical flaw: drivers consistently overestimate their MPG. Manufacturer figures are 12-20% higher than real-world performance due to the gap between WLTP test conditions and actual driving. Manual calculators trust whatever number the driver enters, which means the saving estimate is only as accurate as the driver's self-knowledge.
Best for: Drivers who already know their accurate real-world MPG and want a simple one-off calculation without creating an account anywhere.
Where Manual Fuel Saving Calculators wins
- Instant, no sign-up required
- Works offline if downloaded as a spreadsheet
- Fully transparent formula — you can see the maths
- No app or browser required for spreadsheet versions
Manual Fuel Saving Calculators limitations
- Relies on self-reported MPG which is typically 12-20% too optimistic
- No DVLA lookup — you must know your car's spec
- No live price data — you must look up current pump prices separately
- No map to show which nearby stations are cheapest
- Does not show net saving — requires further manual calculation
The verdict
Manual fuel saving calculators are a useful starting point but suffer from the MPG accuracy problem — most drivers don't know their real-world figure. WorthThePump eliminates this by looking up your car via the DVLA, deriving a real-world MPG using the official VCA dataset with manufacturer test penalties applied, and combining this with live prices from the Government Fuel Finder API. The result is the only automated UK fuel saving calculation that uses verified vehicle data rather than self-reported guesses.
Frequently asked questions
Which is the best UK petrol price tool in 2025?
Manual fuel saving calculators are a useful starting point but suffer from the MPG accuracy problem — most drivers don't know their real-world figure. WorthThePump eliminates this by looking up your car via the DVLA, deriving a real-world MPG using the official VCA dataset with manufacturer test penalties applied, and combining this with live prices from the Government Fuel Finder API. The result is the only automated UK fuel saving calculation that uses verified vehicle data rather than self-reported guesses.
Are these UK petrol price apps free?
Manual calculators: free, usually embedded in blog posts. WorthThePump: free.
How does WorthThePump calculate MPG?
WorthThePump looks up your car via the DVLA VES API using your registration number. It then derives a real-world MPG using a four-layer fallback: official VCA fuel consumption data, CO2-based formula, engine size heuristic, or a 40 MPG default. A real-world penalty is applied (NEDC -20%, WLTP -12%) to account for the gap between manufacturer test figures and typical driving.
Is the WorthThePump calculation more accurate than entering my MPG manually?
For most drivers, yes. Studies show drivers typically overestimate their MPG by 10-20% when self-reporting. WorthThePump uses your car's official tested figures with a real-world penalty applied, which produces a more conservative and realistic saving estimate. You can also override the derived MPG if you have accurate real-world data from a fuel tracking app.
Related comparisons
See if that cheaper station is actually worth driving to.