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HoldingCost

Fuel cost calculator

Estimate annual, monthly, and per-km fuel cost — with optional head-to-head comparison against another vehicle's consumption.

Calculator vehicles

Logic updated April 2026

This calculator estimates your annual and per-kilometre fuel cost from three inputs: how far you drive each year, your vehicle's fuel consumption per 100km, and the price you pay per litre. Optionally, it compares against a second vehicle's consumption to show the dollar savings from switching to a more efficient model.

How this is calculated

Formula 

annualFuelCost = annualKm × consumptionL100km / 100 × pricePerLitre ; costPerKm = annualFuelCost / annualKm

Step-by-step

  1. Calculate litres burned per kilometre: consumption per 100km ÷ 100
  2. Multiply by annual kilometres to get annual litres burned
  3. Multiply by price per litre to get annual fuel cost
  4. Divide annual cost by 12 for a monthly figure that's easier to budget against
  5. Divide annual cost by annual km to get cost per kilometre — useful for comparing vehicles or budgeting per-trip
  6. If a comparison vehicle is supplied, calculate its annual cost the same way and report the dollar saving (positive when the comparison consumes more)
Rounding mode
ROUND_HALF_UP
Precision
20-digit internal precision (Decimal.js), rounded to 2 decimal places for display
Logic last reviewed

Assumptions & limitations

What this calculator assumes

  • Fuel consumption and fuel price remain constant over the period
  • Annual km is driven at a consistent rate across months
  • Break-even km is the annual km required to realise $1,000 in annual fuel savings against the comparison vehicle

What this calculator doesn’t account for

  • Does not model fuel price changes throughout the year
  • Does not account for difference between manufacturer-rated consumption and real-world consumption
  • Does not factor in driving conditions (urban stop-start vs highway)
  • Does not include premium vs regular fuel grade differences
  • Does not factor in additives, oil, or other fluids associated with running the engine

Worked example

A driver covers 18,000 km a year in a vehicle averaging 8.5L/100km, with fuel at $1.85 per litre.

Input Value
Annual km 18,000
Consumption 8.5 L/100km
Fuel price $1.85/L

Annual fuel cost: $2,830.50 — Monthly: $235.88 — Cost per km: $0.16

Litres per year = 18,000 × 8.5 ÷ 100 = 1,530 L. Annual cost = 1,530 × $1.85 = $2,830.50. Per km = $2,830.50 ÷ 18,000 = $0.157. If the same driver switched to a 6.5L/100km car, annual fuel would drop to $2,164 — a $666/year saving and 3 cents/km cheaper to run. Over 5 years that's $3,330 in fuel alone.

Frequently asked questions

How to calculate fuel cost per kilometre?

Divide your annual fuel cost by the annual kilometres driven. For a quick estimate without tracking annual totals: (consumption per 100km × price per litre) ÷ 100. A vehicle that uses 7L/100km at $1.80/L costs (7 × $1.80) ÷ 100 = $0.126 per kilometre. Multiplied by typical annual distances of 12,000–20,000 km, that's $1,500–$2,500 a year.

Real-world vs manufacturer consumption?

Manufacturer consumption ratings are measured under controlled lab conditions. Real-world consumption is typically 15–30% higher due to traffic, terrain, climate control use, and how aggressively you drive. Use the rated figure as a starting point but plug in a real-world number (most vehicles have a trip computer that shows lifetime average consumption) for a more accurate cost.

How does driving style affect fuel cost?

Aggressive acceleration and high-speed cruising can increase fuel consumption by 20–40% over moderate driving. Smooth acceleration, anticipating stops, and cruising at 90–100 km/h instead of 110+ all measurably reduce consumption. Tyre pressure, roof racks, and excess weight also matter — checking pressures monthly typically saves 1–3% on fuel.

Petrol vs diesel running costs?

Diesel engines typically use 15–25% less fuel per kilometre than equivalent petrol engines, but diesel fuel often costs more per litre and diesel vehicles cost more to buy and service. The break-even depends heavily on annual kilometres — diesel usually wins above 25,000 km/year, petrol wins below 15,000. This calculator handles either fuel type if you enter the right consumption and price.

How does annual km change the fuel cost calculation?

It scales linearly. Doubling your annual kilometres doubles your annual fuel cost, since consumption rates and fuel prices are independent of distance. The cost per kilometre stays the same — it's just multiplied across more kilometres. Long-distance drivers should weight fuel cost heavily when choosing a vehicle; short-distance drivers should weight depreciation more, since fuel is a smaller part of their total cost.

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