Determine the amount of mileage that you will incur over a set period of time. For example, suppose you will drive your car 15,000 miles over a period of one year.
Find out the miles per gallon and the recommended oil change mileage for the vehicle. This information is included in the dealer's handbook provided at the time of purchase. You can also find it online (see Resources). Suppose a car gets 30 miles per gallon, and you must change the oil every 5,000 miles.
Divide the total mileage by the miles per gallon of the car. In this case, 15,000/30 = 500 gallons. Divide the total mileage by the recommended oil change mileage. In this case, 15,000/5,000 = 3 oil changes.
Multiply the number of gallons by the price of gas per gallon. For example, if gas is $3.50 per gallon, then 3.50*500 = $1,750. Multiply the number of oil changes by the price of an oil change. For example, if an oil change is $40, then 40*3 = $120.
Sum the total gas price with the total oil price to yield the total overall estimate. In this case, the overall estimate is 1,750+120 = $1870.