Compare Car Running Costs

Compare the full annual running cost of two cars side by side — petrol vs diesel, diesel vs electric, or any combination. Enter each car's MPG (or kWh per mile for electric), annual mileage and fixed costs to see which is cheaper to run over a year. For the most accurate fuel cost, use your real-world MPG from our MPG calculator rather than the manufacturer's figure.

Compare the Running Cost of Two Cars, Petrol, Diesel or Electric

Enter your figures above and click Calculate to see your result.

How to compare car running costs

The true cost of running a car is more than just fuel. To compare two vehicles fairly, you need to account for five categories of annual expenditure:

  • Fuel (or electricity) — calculated from your annual mileage, real-world MPG and the price per litre. For electric vehicles, it's pence per kWh multiplied by consumption per mile, split between home and public charging rates.
  • Road tax — varies by CO₂ emissions, fuel type and vehicle age. Electric vehicles registered before April 2025 pay no road tax; newer EVs pay the standard flat rate.
  • Insurance — typically higher for diesel and electric cars due to higher repair costs, though this varies by model and driver.
  • Servicing and repairs — diesel engines cost more to service. Electric vehicles have far fewer moving parts and lower maintenance costs, but tyre wear can be higher due to extra weight.
  • Depreciation — often the largest single cost. EVs have historically depreciated faster, though this is narrowing as demand increases.

This calculator combines all five to give you a single annual figure for each car, making it easy to see which is genuinely cheaper to own.

Petrol vs diesel vs electric — which is cheapest?

There's no single answer — it depends on how far you drive each year. Here's a rough guide:

  • Under 8,000 miles/year — petrol is usually cheapest. Lower purchase price and insurance outweigh the higher fuel cost per mile.
  • 8,000–15,000 miles/year — diesel starts to break even. The better fuel economy offsets the higher fixed costs. Use our break-even calculator to find the exact crossover for your cars.
  • Over 15,000 miles/year — diesel or electric often wins. At high mileages, the per-mile fuel saving dominates and total annual cost can be significantly lower.

The calculator above lets you plug in your actual numbers rather than relying on generalisations. The breakeven chart shows exactly at what mileage one car becomes cheaper than the other.

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Frequently Asked Questions

Yes. The calculator supports petrol, diesel and electric vehicles. For electric cars you can split charging costs between home and public charging to reflect real-world usage.

The calculator includes annual fuel or electricity cost, road tax, insurance, servicing and repairs, and depreciation. These are combined to give a total annual cost for each car.

The results are as accurate as the figures you enter. For the most accurate fuel cost, use your real-world MPG from our MPG calculator rather than the manufacturer's figure.

It depends on your annual mileage. Diesel cars are more fuel-efficient but typically cost more to buy, insure and service. At higher mileages (roughly 12,000+ miles per year) diesel can work out cheaper overall. Use the petrol vs diesel break-even calculator to find the exact crossover point for your situation.

Electric cars are significantly cheaper per mile on fuel alone — home charging typically costs a third of what petrol costs per mile. However, higher purchase price and depreciation can offset the saving. This calculator lets you compare the full annual picture including all costs, not just fuel.

Use your real-world MPG, not the manufacturer's official figure. WLTP figures are typically 15–25% higher than what you'll achieve in everyday driving. Use our MPG calculator to measure your actual fuel economy from a fill-up.

Yes, significantly. Fixed costs like insurance, road tax and depreciation stay the same regardless of mileage, but fuel costs scale directly with miles driven. A diesel or electric car with lower fuel cost per mile becomes increasingly cheaper than a petrol car as your annual mileage rises.