Term in months for your auto lease or your auto loan.

Amount paid as a down payment, which for leases is often called a capital reduction.

Any fee, other than a capital reduction or down payment, required to be paid at the close of the lease or loan. This may include license, title transfer fees, etc.

Total purchase price. Price should be after any manufacturer's rebate.

Annual interest rate for your loan or your lease.

Percentage sales tax to be charged on this purchase. Sales tax is included in each lease payment. Sales tax for buying is charged on the total sale amount.

The rate of depreciation gauges how fast your new automobile will lose its market value. A high depreciation rate is about 20% per year, medium is 15% per year and low is 10% per year.

For leases, this is remaining value after the lease term expires. The higher this amount, the lower your lease payment will be.

Value of your auto after the lease term is over.

Rate of return on investments. This is the return that you would make if you were to invest your down payment or security deposit instead of using it in your auto purchase or lease.

The actual rate of return is largely dependent on the type of investments you select. For example, from December 1999 to December 2009, the average annual compounded rate of return for the S&P 500 was -0.6%, including reinvestment of dividends. From January 1970 to December 2009, the average annual compounded rate of return for the S&P 500, including reinvestment of dividends, was approximately 10.1% (source: www.standardandpoors.com). Since 1970, the highest 12-month return was 61% (June 1982 through June 1983). The lowest 12-month return was -43% (March 2008 to March 2009). Savings accounts at a bank may pay as little as 1% or less but carry significantly lower risk of loss of principal balances.

It is important to remember that these scenarios are hypothetical and that future rates of return can't be predicted with certainty and that investments that pay higher rates of return are generally subject to higher risk and volatility. The actual rate of return on investments can vary widely over time, especially for long-term investments. This includes the potential loss of principal on your investment. It is not possible to invest directly in an index and the compounded rate of return noted above does not reflect sales charges and other fees that funds and/or investment companies may charge.

This includes any interest you would have earned at your investment rate of return on the buy option's down payment and other fees. If the monthly payment for leasing is less than the monthly payment for buying, this also includes any lost interest due to the higher monthly payments. If leasing is more expensive than buying, your interest costs for buying are reduced by the amount of interest you would earn on the difference.