Monthly fuel cost calculator

How this is calculated

Weekly miles are the one-way commute times 2 times the days per week, plus any extra miles. Weekly cost is those miles divided by your mpg, times the price per gallon. The yearly cost is the weekly cost times the weeks you drive, and the monthly cost is the yearly cost divided by 12.

weekly cost = (one-way miles × 2 × days + extra miles) ÷ mpg × price

The method, the constants and the limits are written out in how fuel cost is calculated.

Using it to budget

Gas is a cost that comes in small pieces, so the monthly total can be a surprise. Enter your commute and the days you actually drive, add errand miles if you want them counted, and compare the monthly figure with what you think you spend. If your weeks vary, lower the weeks per year to leave out holidays or remote weeks.

What a price change does

The monthly gas use does not depend on the price, so a price change is easy to work out by hand: multiply it by the gallons used per month. If you use 25 gallons a month, a 50-cent rise adds 25 × $0.50 = $12.50 a month, and a 50-cent drop saves the same.

When mpg changes with the seasons

Most cars use more fuel in cold weather and with the air conditioning on, so one mpg figure for the whole year is a simplification. If you know your winter and summer figures, run the calculator once with each, then average the two monthly costs weighted by how many months each season lasts. Working out each from fill-ups is covered by the fuel consumption calculator.

For a single trip rather than a routine, use the fuel cost calculator. To see what your car costs per mile including the other costs, use the cost per mile calculator. To split the fuel cost with a carpool, there is the gas money calculator, and the EV vs gas cost calculator compares yearly energy costs with an electric car.