You might face another choice that involves promotional low-interest deals. Let’s say Chrysler offers a reduced interest rate on the Dodge Caravan. It sounds attractive to go with that low-cost dealer financing. But wait. Let’s also say you have an alternative choice of taking a cash rebate, which is common these days.

In this case, your decision will depend on how low the promotional rate is. You can readily figure out your alternatives with Web site calculators. For instance, if you’re buying a Dodge Grand Caravan at an attractive negotiated price of about $20,000, and you put down 10 percent, your loan amount would be $18,000. If you take a $1,000 rebate, cut that principal to $17,000 and get a regular, 8 percent auto loan, your monthly payment on a four-year loan would be $415.02.

If the promotional rate is the common 5.9 percent, taking that instead of the rebate would produce monthly payments of $421.91. The rebate is a slightly better deal. But if the manufacturer cut the rate to 1.9 percent, monthly payments on a four-year loan would be $389.73 — the clear winner.