Compare the fuel cost of two cars
Two cars, two consumption figures, two fuel prices. What the difference actually adds up to over the years you will keep it.
Your figures
Result
- Car A per year
- $1,395
- Car B per year
- $1,088
- Difference per month
- $25.63
- Difference over 5 years
- $1,538
- Car A per unit of distance
- $0.093
- Car B per unit of distance
- $0.073
Over time
| Period | Car A | Car B | Difference |
|---|---|---|---|
| Al mes | $116 | $91 | $26 |
| Per year | $1,395 | $1,088 | $308 |
| Over 5 years | $6,975 | $5,438 | $1,538 |
| Over 10 years | $13,950 | $10,875 | $3,075 |
What we assume
- This compares fuel only. Purchase price, insurance and maintenance can reverse the conclusion completely.
- Separate fuel prices are allowed on purpose, so you can compare petrol against diesel, or either against electricity.
- Constant consumption and constant fuel prices are assumed over the whole period, which is optimistic on both counts.
How it is calculated
Each car costs distance times consumption times price, per year. The comparison is then projected over five and ten years, which is where a small difference stops looking small.
Why the fuel price matters as much as the consumption
A car using less fuel can still cost more to run if its fuel is dearer. That is the whole petrol-versus-diesel argument, and it is why the two prices are separate fields rather than one: comparing consumption alone answers the wrong question.
What this does not settle
Whether to buy. A car that saves 300 a year in fuel and costs 4,000 more takes over thirteen years to break even, by which time depreciation has dwarfed the whole calculation.
An example
At 15,000 a year, a car at 6 l/100 km and 1.55 costs about 1,395 a year; one at 5 l/100 km and 1.45 costs about 1,088. That is roughly 26 a month, or 1,500 over five years.
Frequently asked questions
Can I compare petrol against electric?
Yes. Put the electric car consumption in kWh per 100 and its price per kWh in the fuel price field. The arithmetic is identical.
Does a lower consumption always win?
No, and that is the point of having two price fields. A more efficient car burning a dearer fuel can easily come out worse.
Should I buy the more efficient one?
Not on this alone. Work out how many years the fuel saving takes to cover the price difference, and compare that with how long you plan to keep the car.
Keep calculating
All tools →- Real fuel economy calculatorFuel put in and distance covered. That is all it takes to know what your car really does, rather than what the trip computer claims.
- Cost per unit of distance of your carFuel is the part you notice and the smallest part of the bill. This adds the ones you do not: insurance, tax, servicing and, above all, depreciation.
- Electric car charging costWhat a charge costs and how far it takes you. Including the energy you pay for that never reaches the battery, which nobody mentions.
Updated on 2026-08-26. Calculations run in your browser; nothing you type is sent to a server.