Set annual kilometres, EV consumption, electricity price, fuel consumption and price per litre. Use comparable routes and driving patterns for both vehicles. For the EV, a consumption figure measured from the grid includes the charging energy you actually pay for.
Formula
Annual EV cost = annual km ÷ 100 × kWh/100 km × electricity price. Annual fuel cost = annual km ÷ 100 × litres/100 km × price per litre. Saving = fuel cost − EV cost; percentage saving uses fuel cost as its baseline.
Worked example
Over 15,000 km, an EV using 18 kWh/100 km requires 2,700 kWh. A combustion vehicle using 6 litres/100 km requires 900 litres. Applying the respective unit prices gives a like-for-like annual energy comparison.
What the result means
A positive saving means lower energy spending with the electric vehicle under these assumptions. A negative result means the entered charging arrangement costs more than the fuel scenario.
Electricity price · United Kingdom
Enter the unit rate including any applicable tax. Check your bill rather than adding a tax percentage automatically. Standing charges, export payments and subscription fees are separate. Ofgem information applies to Great Britain; Northern Ireland has its own regulator and market arrangements.
Assumptions and limits
This is an energy-cost comparison, not a total ownership forecast. Depreciation, purchase price, taxes, insurance, maintenance and infrastructure costs can change the overall decision.
Questions answered
Can I compare diesel instead of petrol?
Yes. Enter the diesel vehicle’s litres per 100 km and diesel price.
Does it include public charging fees?
Only the per-kWh price entered. Add other fees separately when assessing a real offer.
Data sources
- Ofgem · July–September 2026
- Ofgem: Understanding electricity and gas bills
- Ofgem: Price cap and standing charges explained
- Utility Regulator: Consumer information for Northern Ireland
- EPA · EV range and energy testing
Last reviewed: 2026-09-08