Methodology

The calculator compares the annual fuel and electricity running costs of a petrol or diesel car against an equivalent electric vehicle. It does not include purchase price, depreciation, insurance, servicing, road tax, or finance costs — these vary too much between vehicles and circumstances to be included reliably.

All calculations run entirely in your browser. No personal data, no postcode, and no inputs are transmitted to or stored on any server beyond a postcode lookup (which is handled via the free postcodes.io API).

We convert MPG to litres per 100 km, then calculate annual litres consumed and multiply by your local fuel price.

4.54609 is the number of litres in one Imperial gallon (UK standard).

We calculate kWh consumed per year from your EV efficiency, then apply a blended electricity rate based on your home vs public charging split.

The home vs public charging split has a large impact on results. Home charging at 26.1p/kWh (the Ofgem price cap rate for July–September 2026) gives roughly 7.5p per mile for a typical EV. Public rapid charging averaged 79p/kWh across UK networks in mid-2026 and pushes that to around 22.6p per mile — more expensive than many petrol cars.

A positive value means EV is cheaper. A negative value means petrol / diesel is cheaper with your current assumptions.

Break-even is only shown when the annual saving is positive (EV is cheaper). The EV price premium defaults to £2,500 — an approximate difference between a popular mid-range EV and its petrol equivalent, after government grants where applicable. Adjust this to reflect your own comparison.

• ⚠Results cover fuel and electricity running costs only. Insurance, depreciation, servicing, road tax, and finance can add £2,000–£5,000+ per year and are not included.
• ⚠Official MPG figures are typically 10–25% higher than real-world fuel economy. Consider reducing the MPG figure to reflect your driving style.
• ⚠EV real-world efficiency varies significantly with speed, temperature, load, and driving style. Winter efficiency can be 20–30% lower.
• ⚠Public charging prices change frequently and vary by network, location, and subscription. Check Zap-Map or individual network apps for current pricing.
• ⚠Home electricity rates depend on your tariff. EV-specific overnight tariffs (e.g. Octopus Go) can reduce home charging costs to 7–10p/kWh — dramatically improving EV economics.
• ⚠Fuel prices are national averages. Local prices vary by up to 20p/litre. Enter your postcode for live local pricing from nearby forecourts.
• ⚠This tool does not constitute financial advice. Always verify costs with your own research before making purchasing decisions.

• Fuel prices: RAC Fuel Watch national averages — updated manually in fallback data. Live local prices are fetched via the CMA Fuel Finder API when a postcode is entered.
• Electricity rates: Ofgem price cap quarterly updates for standard variable tariff rate.
• Public charging rate: Zapmap's UK charging price index, rapid/ultra-rapid weighted average.
• Postcode lookup: postcodes.io (free, open source).
• EV efficiency: Real-world data from Spritmonitor, WLTP test data, and EV Database.
• Gallons conversion: 1 UK Imperial gallon = 4.54609 litres (BIPM definition).