When you use a cosigner, most lenders base the maximum payment on the lower of the borrower's income and the cosigner's income. The interest rate and repayment terms are typically based on the cosigner's credit. If the cosigner has a good credit score, it can result in a lower interest rate, potentially saving the borrower thousands over the loan term. However, if the cosigner's income is significantly lower than the borrower's, it might limit vehicle choices.