Fuel Savings Calculator
Compare two vehicles’ fuel costs and see what switching would save.
Please note: Estimates for planning only. Real fuel economy, depreciation, insurance and lease terms vary widely by vehicle, region and driving style. Confirm figures against a dealer quote or your own records before relying on them.
What the Fuel Savings Calculator does
Comparing two vehicles on fuel means converting both to a consumption basis — litres per 100 km — because miles per gallon is a reciprocal measure. That reciprocal is why improving a thirsty car by 5 mpg saves far more fuel than the same 5 mpg gain on an already efficient one.
Formula
Litres per year = Distance ÷ 100 × L/100kmAnnual saving = (Current litres − New litres) × Price per litrePayback = Extra vehicle cost ÷ Annual saving
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Distance driven per year | number | Yes | Accepts more than 0. |
| Distance unit | one of 2 options | Yes | — |
| Current vehicle economy | number | Yes | Accepts more than 0. |
| New vehicle economy | number | Yes | Accepts more than 0. |
| Fuel economy measured in | one of 4 options | Yes | — |
| Fuel price per unit | selected currency | Yes | Accepts more than 0. |
| Fuel priced per | one of 3 options | Yes | — |
| Extra cost of the new vehicle | selected currency | Optional | Accepts 0 or more. |
| Years to project | number | Yes | Accepts 1 or more, up to 20. |
| Fuel type | one of 4 options | Optional | Used for the CO₂ estimate. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Distance unit and Fuel economy measured in.
- Enter Distance driven per year, Current vehicle economy, New vehicle economy and Fuel price per unit and 1 more.
- Optionally add Extra cost of the new vehicle.
- Select Calculate.
Worked example
Swapping a 22 mpg car for a 35 mpg one, driving 12,000 miles a year with fuel at $3.50 a gallon.
- Distance
- 12,000 mi
- Current
- 22 mpg
- New
- 35 mpg
- Fuel
- $3.50/gal
545.5 gallons drops to 342.9 — a saving of 202.6 gallons, or $709 a year and $3,545 over five years.
Frequently asked questions
Why does mpg mislead when comparing cars?
Because it is fuel economy, not consumption. Going 10→20 mpg halves fuel use; 40→50 mpg cuts it by only a fifth. Litres per 100 km avoids the trap by being linear.
Does a more efficient car always pay for itself?
Only if the fuel saving outruns the price premium within your ownership period. High mileage drivers reach payback far sooner.