Include more than fuel in annual costpermile calculations to find out how much it actually costs to drive a mile. Start with your current vehicle, and then use this information to compare annual costs for a newer or more efficient vehicle. You can also use costpermile information to see how much more you can potentially save each year by ditching your car and telecommuting, or if that’s not possible, by riding a bike or taking a bus to work.
Start With Fuel Cost

Although fuelcost calculations are more accurate when you have a log containing fuel and mileage information, you can use estimates if historical information isn’t available. Divide total actual or estimated fuel expenses by actual or estimated annual miles driven to calculate annual fuel cost per mile. For example, if you drove 15,000 miles and spent $1,600 on fuel over the past year, your fuel cost is 1,600 divided by 15,000, or 10.67 cents per mile.
Include Operating Costs

Calculate total operating costs and then divide this amount by annual miles driven. Include regular maintenance such as routine servicing, car washes, detailing, tires and wiper blades. Also, include money you paid for emergency repairs, including any outofpocket deductible expenses for insurance claims. Make sure to include unreimbursed parking and toll fees if these apply. If you spent $5,000 last year to operate a vehicle and drove 15,000 miles, your operating cost is 5,000 divided by 15,000, or 33.33 cents per mile.
Determine Annual Ownership Costs

Ownership costs are the annual expenses you incur by virtue of owning a vehicle. These include insurance, depreciation, license and registration fees, finance charges on an outstanding loan and taxes if your state has a salestax requirement. Gather the information required for calculating ownership cost  except for depreciation  by referring to documents you have on hand. The easiest way to calculate depreciation is by using an online calculator, available on websites such as MoneyZine.com, Edmunds.com or CarPrice.com. However, because most calculators determine total rather than annual depreciation, you’ll need to divide total depreciation by the years you’ve owned the vehicle to determine average annual depreciation.
Consider Indirect Costs

Include commute time and estimates of potential accident cost to create an evenclearer picture of true driving costs. Because travel costs depend on the frequency and length of your commute, World Bank economist Kenneth Gwilliam recommends using 15 to 30 percent of your hourly wage as a good default estimate. If you make $25 per hour, spend one hour driving to and from work each day and use 15 percent, travel costs total $3.75, or about $975 per year. Divide this amount by total annual commute miles to calculate the cost per mile. Contact your insurance agent to get information on accident cost per mile or consider an estimate of 10 to 12 cents per mile.
Calculate Total Driving Costs

Add and convert total ownership costs to ownership costs per mile. If you spent $3,000 last year in ownership costs and drove 15,000 miles, your ownership cost is 3,000 divided by 15,000, or 20 cents per mile. Add fuel and operating costs per mile to this amount to get a final cost per mile. For example, if fuel costs are 10.67 cents, operating costs are 33.33 cents, ownership costs are 20 cents and indirect costs total 25 cents, you spend about 89 cents for every mile you drive.
References
 AAA.com: Your Driving CostsHow Much Are You Really Paying to Drive?
 CarsDirect.com: How to Find and Use a Car Depreciation Calculator
 CommuteSolutions.org: How Much Does it Really Cost You to Drive?
 Victoria Transport Policy Institute: Transportation Cost and Benefit Analysis II – Travel Time Costs
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