Auto loan calculators allow you to estimate your monthly payment depending on the cost of the car, your down payment, the loan term, and the interest rates. Lots of websites have great calculators available, and it’s not a bad idea to play around with them a bit and do some research before you ever start shopping, just so you have an idea of what you can afford and what you can’t.

Bankrate.com is a terrific website with a great auto loan calculator and lots of solid basic information on what to look for when shopping for a car and financing for the car. You can check out the bankrate.com calculator at http://www.bankrate.com/brm/auto-loan-calculator.asp.

One especially nice feature of the bankrate.com auto loan calculator is that it allows you to figure out how much time and money making extra payments on your auto loan will save over the life of the loan. This can be a real eye-opener. For example, if you borrow $15,000 for 48 months on a new car at 10% interest, your monthly payment will be $380.44. If you add $40 extra to your monthly payment you will pay the loan off three months early and save yourself $385 in interest over the life of the loan.

In general, the shorter the term of your auto loan, the better the interest rate and the lower the cost of borrowing. If you finance the same $15,000 car for 36 months at 8% your monthly payment would be $470.05, but over the life of the loan you would save yourself a staggering $1341 in interest.

Another useful auto loan calculator at cars.com lets you plug in the cost of the new car, the trade in value of your old car, your down payment, the taxes, and the interest and loan term to get your payment. On the same $15,000 car, if you put $1000 down and trade in your old vehicle for $4000, assuming sales tax at 5% or $750, you end up with a monthly payment on a three-year 8% loan of $336.86, shaving almost $150 per month off your payment with nothing down and no trade-in.

Edmunds.com is a great website for checking out the auto loan calculator, because not only can you plug in all the features available at the other sites, you can also find out the fair trade-in value on your old car.

MSN Money lets you find out the current auto loan rates in your specific area by zip code and then get an estimate based on that and the cost of the car you want to buy.

MSN Money’s auto loan site also shows you the current national average for auto loans at low, average, and high costs. You can also apply for an auto loan from any of the sponsors of the site directly from the calculator page. These features are available at the MSN site at http://moneycentral.msn.com/loan/loan.aspx?iType=3&pkw=auto_loan_calculators&vendor=google&refcd=go210919s_auto_loan_calculators&tsacr=go558940140.

Yahoo lets you compare lease and loan options and the cost of each by providing three different auto loan calculators at http://autos.yahoo.com/finance/loan-calc/.  As with a number of auto loan calculator sites, you can also find the value of the car you are buying and the car you want to trade in, and apply directly for a loan right from the calculator page.

When calculating the cost of an auto loan, most people only care about the monthly payment. If you are not prepared before you shop, the car salespeople will also focus on the monthly payment. They do this in order to sell you the most expensive car they possibly can, which is always good for them, but may or may not be good for you, depending on your situation.

Using a variety of auto loan calculators before you shop will enable you to focus on the true cost of the loan. If you finance $15,000 for three years at 10% interest, you will have the same monthly payment as if you finance $23,000 for five years at the same rate, but you will end up paying $3896 more in interest to the bank on the five year loan. Plus, you will be making payments for two additional years.