The exact interest cost behind a mortgage, car loan, or refinance.
It depends on the rate and term, but over a 30-year mortgage or a 6-7 year car loan, total interest paid can add tens of percent on top of the amount borrowed. Each tool on this page breaks that interest total out on its own line, next to the monthly payment.
Refinancing saves money when the interest saved over the remaining term outweighs closing costs and any rate-lock or prepayment fees, and that break-even point depends on how long you keep the loan after refinancing, not just the new rate being lower.