How to Calculate the Cost of Driving

Calculating Fuel Costs

Calculate fuel costs by writing down the number of miles or kilometers on the odometer when the fuel tank is nearly empty.

Fill the tank when it is near empty. Do not top off the tank.

Refill the tank when it is near empty again and write down the number of gallons or liters it took to fill. Do not top off when refilling.

Check the odometer again at refilling and subtract the old number on the odometer from the new number to see how far you drove. Write down the difference between the two odometer readings. If the number was 30,000 miles (48,280 km) when you filled the tank the first time and 30,300 (48,763 km) when you refilled, you drove 300 miles (482.8 km) on 1 tank of gas.

Divide the number of miles or kilometers you drove by the number of gallons or liters it took to refill your tank. For example, if you drove 300 miles (482.8 km) and burned 15 gallons (56.78 liters) of gasoline, your vehicle got about 20 miles per gallon (8.5 km per liter).

Divide the distance driven in a month by the miles or kilometers per gallon or liter. (If your car has 30,000 miles [48,280 km] and is 40 months old, you drive about 750 miles [1,207 km] per month.) In this hypothetical example, divide 750 (1,207 km) by 20 gallons (75.7 liters) to get the number of gallons or liters you burn per month: 37.5 gallons (142 liters).

Multiply the total amount of fuel per month you burn by the cost of a gallon or liter of gasoline to get your monthly fuel costs. If gas costs $4 per gallon ($1.05 per liter), you spend $128 per month on fuel, or 17 cents per mile (10 cents per km).

Maintenance and Insurance

Add up what you spend in a year on oil changes, tires and other maintenance, car repair bills, and insurance. Divide this total by 12 to get the monthly total. If the total is, for example, $1,890 per year, the monthly cost for maintenance, repairs and insurance is $157.50 per month.

Add inspection and registration costs for a year and divide by 12. If the total is $100 per year, the monthly cost is $8.33.

Costs of Driving

Add the monthly totals for fuel ($128 in our example); maintenance, repairs and insurance ($157.50 a month); and inspection and registration ($8.33) to see how much it costs to drive the automobile per month. In the hypothetical scenario we used, the cost to drive the fictional car per month would be $293.83 per month.

Divide vehicle operation costs, $293.83 per month in our hypothetical scenario, by the distance you drive per month, 750 miles (1,207 km) in our example, to calculate the cost per mile. The cost per mile for this hypothetical driver and vehicle is 39.17 cents per mile or 24 cents per kilometer.

Note that the costs in this calculation do not include finance charges drivers pay to buy the vehicle, travel time, depreciation of the automobile's value, accidents, parking and tolls, and societal costs of taxes and other costs from factors such as road construction and pollution abatement. One website calculates the cost of driving the average car at $1.41 per mile (83 cents per km) with all costs factored in.