Petrol vs Diesel Break-Even

Diesel cars typically cost more to buy but use less fuel per mile. Enter the two cars' MPG figures, current fuel prices, the diesel price premium and your annual mileage to see when — if ever — the diesel version pays back its higher purchase price.

Petrol vs Diesel Break-Even Calculator
Mileage & Fuel Prices
Car Specs & Costs
Annual Other Costs — Petrol
Annual Other Costs — Diesel
Annual Running Costs
PetrolDiesel
Fuel£2157.57£1801.24
Other (tax, servicing, depreciation, insurance)£0.00£0.00
Total annual£2157.57£1801.24
Fuel saving (diesel vs petrol)£356.33/yr diesel saves
Net saving after other costs£356.33/yr diesel saves
Cumulative Cost Over Time (incl. £1500 diesel premium)
YearPetrolDieselDiesel saves
1£2158£3301-£1144
2£4315£5102-£787
3£6473£6904-£431
4£8630£8705-£75
5£10788£10506+£282
7£15103£14109+£994
10£21576£19512+£2063

Example based on default values — enter your own figures above and click Calculate.

How the Petrol vs Diesel Break-Even Is Calculated

Diesel cars almost always cost more to buy new than the equivalent petrol model — sometimes by £1,500 to £3,000. In return, they typically use 15–25% less fuel per mile. The break-even point is the annual mileage at which those fuel savings finally cancel out the higher purchase price.

The calculator takes:

  • The MPG of each version (petrol and diesel),
  • The current pump price per litre for each fuel,
  • The diesel purchase premium (the extra you pay for the diesel model),
  • Annual mileage and any other recurring costs (insurance, road tax, servicing, depreciation),

and works out the per-mile cost for both. From there it calculates how many years — at your chosen mileage — the diesel takes to pay back its premium through fuel savings alone.

Worked Example

Say you're choosing between two versions of the same car: a 35 MPG petrol and a 55 MPG diesel. At today's UK national average pump prices — petrol at 158.2p/litre and diesel at 181.6p/litre — and a £2,000 diesel purchase premium:

  • Petrol cost per mile: 4.546 ÷ 35 × 158.2 = 20.5p
  • Diesel cost per mile: 4.546 ÷ 55 × 181.6 = 15.0p
  • Saving per mile: 5.5p (in favour of diesel)
  • Miles to recoup £2,000 premium: 200,000 ÷ 5.5 ≈ 36115 miles
  • Years at 12,000 miles/year: ≈ 3.0 years

The break-even mileage is highly sensitive to fuel prices — even a few pence per litre swing changes the payback period by years. High-mileage drivers (20,000+ miles a year) almost always come out ahead with diesel; low-mileage town drivers rarely do.

Frequently Asked Questions

Diesel engines are typically 15–25% more fuel-efficient than equivalent petrol engines, but diesel fuel usually costs more per litre. Whether diesel works out cheaper overall depends on your mileage and the purchase price premium of the diesel model.

It varies. With a typical £1,500–£2,000 diesel premium and a 10 MPG advantage, the break-even point is usually between 40,000 and 80,000 miles. At 12,000 miles per year that could be 3–7 years. Use the calculator above to find your exact figure.

Diesel makes most sense for high-mileage drivers who regularly cover long motorway journeys. If you drive mainly short urban trips, petrol or a hybrid is likely more cost-effective. Consider also that diesel cars may face higher charges in low-emission zones.