Fuel Cost Calculator

Annual fuel cost is one of the most overlooked factors when choosing or budgeting for a vehicle. Small differences in fuel efficiency compound into thousands of dollars over a car’s lifetime.

Two conventions, running in opposite directions

This is where most fuel arithmetic goes wrong, so it is worth being explicit. North America quotes economy as miles per gallon, where a bigger number is a better car. Most of the rest of the world quotes litres per 100 kilometres, where a bigger number is a worse car. They are reciprocals of each other, and mixing them up does not give you a slightly wrong answer, it gives you a nonsensical one.

A car at 8.5 L/100km is doing 11.8 km per litre, which is about 28 miles per gallon. A car at 8.5 km per litre is doing 11.8 L/100km, which is about 20 MPG. Same digits, very different car. The dropdown above exists so you can enter whichever figure your dashboard or handbook actually gives you.

There is a second trap in the imperial numbers. A US gallon is 3.785 litres and an imperial gallon is 4.546, so a British car quoting 40 MPG is doing about 33 US MPG. If you are comparing a UK review against a US one, that 20% gap is not the engine.

Annual fuel cost formula: Annual Cost = (Annual Miles / MPG) × Price per Gallon

Or in metric: Annual Cost = (Annual km / (100 / L/100km)) × Price per Liter

Simplified metric: Annual Cost = Annual km × (L/100km / 100) × Fuel Price per Liter

Worked example (imperial): Annual mileage: 15,000 miles. Fuel efficiency: 28 MPG. Fuel price: $3.50/gallon. Annual Cost = (15,000 / 28) × $3.50 = 535.7 × $3.50 = $1,875/year

Worked example (metric): Annual distance: 20,000 km. Efficiency: 8.5 L/100km. Price: $1.60/liter. Annual Cost = 20,000 × (8.5 / 100) × $1.60 = 20,000 × 0.085 × 1.60 = $2,720/year

Cost comparison between two vehicles: Annual Savings = (Miles/MPG_old × Price) − (Miles/MPG_new × Price)

Example: Switching from 22 MPG to 35 MPG at 15,000 miles/year, $3.50/gallon. Old: (15,000/22) × $3.50 = $2,386/year New: (15,000/35) × $3.50 = $1,500/year Annual savings: $886, which over ten years is $8,860 in fuel alone.

Typical annual mileage benchmarks:

• US average: 13,500 miles (21,700 km)
• High commuter: 20,000–25,000 miles
• Low use / retiree: 5,000–8,000 miles