Completely fill your car's fuel tank at the beginning of the month. Record the vehicle's odometer reading. The odometer is located below the speedometer on the car's dash board. The odometer keeps track of total miles the car has been driven. For example, the odometer reading might be 45,300 miles.
Completely refill the tank when empty and record the number of gallons it took to refuel. Also, write down the odometer reading. For example, the car might have needed 12 gallons of fuel and have an odometer reading of 45,612.
Subtract the first odometer reading from the second reading to get the distance traveled in miles. Continuing the example, you have 45,612 miles minus 45,300 miles , or 312 miles.
Divide the miles driven until refueling by the number of gallons of fuel added to get the gas mileage in miles per gallon. Now you have 312 miles divided by 12 gallons, or a gas mileage of 26 miles per gallon.
Write down the odometer reading at the end of the month. Subtract the beginning of the month mileage from the end of the month mileage to get the miles total driven in a month. Assume the end of the month mileage was 47,200 miles. Performing this step leads to 47,200 miles minus 45,300 miles, or 1,900 miles.
Divide the number of miles driven for a month by the gas mileage to obtain the number of gallons of fuel required. This step, for example, yields 1,900 miles divided by 26 miles per gallon, or 73.1 gallons.
Multiply the number of gallons of fuel by the current cost of gasoline to get the total cost of fuel needed for driving. Assume the price of gas is $3.59 per gallon. Continuing the example, you have 73.1 gallons times $3.59 per gallon, or a total cost of $262.43.
Add together the costs for parking your car for a month. Include costs for work and leisure. If you pay a flat fee per year to park at your residence, divide the yearly cost by 12 to get the monthly price. Assume, for example, that your monthly parking expense equals $10.
Add together the average monthly cost for oil changes, car insurance and repair bills. Call this result "X." Most people get an oil change every other month, so include half the price of an oil change, or about $15, for monthly costs unless your habits are different. Divide the yearly insurance premium by 12 to get the monthly cost. Assume, for example, a monthly insurance cost of $50. To get an estimate of monthly repair bill cost, add together all repair bills from last year and divide by 12. For example $500 in repairs divided by 12 equals $41.67 per month. Adding the costs together yields $15 plus $50 plus $41.67, or $106.67 for "X."
Add together the yearly costs for state inspection and registration. Then divide by 12 top get the monthly cost. Call this result "Y." For example, $50 for inspection plus $26 for registration equals $76. This yields a monthly cost of $6.33 for "Y."
Add together the monthly cost for fuel plus parking plus "X" plus "Y" to arrive at the total monthly cost to drive the vehicle. Completing the example, you have $262.43 plus $10 plus $106.67 plus $6.33, or a total monthly cost of $385.43.
