My huge blog on auto insurance
When in doubt, be conservative. For instance, if you do not know exactly how much interest you are likely to pay, estimate your interest a little high. If you do not know how much cash you will be able to get back for your old car, estimate a little low. Experiment with the loan calculator, entering a longer or shorter loan term, a higher or lower interest rate, more or less of a down payment, and so forth. Get a sense of how changes in the different factors change the monthly loan payment.