Annual Fuel Cost Calculator

Annual fuel cost calculator for estimating your yearly petrol or diesel budget

Fuel is one of the most expensive running costs for any car, bakkie, or van, and it is also one of the easiest costs to underestimate. This annual fuel cost calculator helps you estimate how much you will spend on fuel over a year based on three things you can usually measure or look up: how far you drive, how efficient your vehicle is, and what you pay per unit of fuel.

The calculator works in both metric and imperial units. If you use kilometres, litres, and L/100 km, select the metric mode. If you think in miles, gallons, and miles per gallon (mpg), select the imperial mode. In either mode, the output shows your estimated fuel used and your fuel cost per year, plus simple breakdowns like monthly and weekly fuel cost. These breakdowns are helpful when you are building a budget, comparing vehicle options, or sanity-checking what a longer commute will do to your cash flow.

To use it, start with your total distance driven per year. If you are not sure, look at last year’s service history, odometer photos, or insurance telematics summaries if you have them. If you only know a weekly distance, multiply it by roughly 52 weeks. Next, enter your fuel economy. For metric users, this is typically shown as L/100 km. For imperial users, this is miles per gallon (mpg). Finally, enter your current fuel price. If your fuel price changes often, you can run the calculator twice: once with today’s price and once with a higher price to see how sensitive your budget is to price changes.

The most useful way to read the result is to focus on the annual total and the monthly estimate. The annual number is great for long-term planning, while the monthly estimate helps you decide whether your current travel pattern is affordable within your normal budget. If you are deciding between two vehicles, change only the fuel economy input and keep distance and price the same to compare the fuel-cost impact of efficiency.

Keep in mind that fuel spend is not perfectly predictable. Real-world fuel economy varies with traffic, driving style, load, tyre pressure, weather, and terrain. Fuel prices also move. This calculator is a planning tool, not a promise. The goal is to get a realistic range so you can make better decisions and avoid being surprised by fuel costs.

Assumptions and how to use this calculator

• Your distance per year is an estimate. If you only know weekly or monthly distance, convert it to an annual total before calculating.
• Fuel economy is assumed to be your real-world average. If your dashboard average differs from the manufacturer rating, use the real-world number.
• Metric mode assumes fuel economy is entered as litres per 100 km (L/100 km).
• Imperial mode assumes fuel economy is entered as miles per gallon (mpg) and fuel price is per gallon.
• Monthly cost is calculated as annual cost divided by 12, and weekly cost is calculated as annual cost divided by 52.

Common questions

What if I do not know my annual distance?

Use a simple estimate. Take your typical weekly driving distance and multiply by 52. If your routine changes seasonally, do two estimates (a normal week and a busy week) and average them. If you have last year’s odometer readings from services or inspections, subtract the older reading from the newer one and use that value.

Should I use the vehicle’s advertised fuel economy?

Only if you have nothing else. Advertised figures are often optimistic compared to real life. If you already own the vehicle, use your actual average from the car’s trip computer or fuel tracking app. If you are shopping, consider adding a buffer by increasing L/100 km (metric) or decreasing mpg (imperial) to avoid underestimating your cost.

Why does my fuel spend change even when my distance stays the same?

Fuel economy and fuel price both change. Traffic, short trips, cold starts, tyre pressure, and extra weight can all increase consumption. Fuel price changes can also move your monthly spend significantly. Running this calculator with a low and high fuel price can show you the realistic range.

Does this include maintenance, tyres, tolls, or insurance?

No. This calculator estimates fuel only. Running costs like maintenance, tyres, toll roads, parking, and insurance can be substantial. If you want a fuller picture, use this result as one line item inside a broader vehicle cost budget.

How do I compare two cars using this calculator?

Keep the same distance per year and the same fuel price, then run the calculator twice with each vehicle’s fuel economy. The difference between the two annual costs is your estimated yearly savings (or extra cost) from fuel efficiency alone.