. >> reporter: the lower rates mean bill and jerry grimes should save enough to renovate a bathroom. they just refinanced in december, now they're re-fi-ing again. >> it's just been amazing. i didn't expect this to happen at this time and this quickly. >> reporter: when should you refinance? experts say if interest rates are at least half a percentage point lower than rate you're currently paying. it may be smart to do the math. a family with a 30-year $300,000 mortgage at 4.5% pays about $1367 a month. but at 3.8% that monthly payment drops by $150. total savings over the life of the loan $22,575. and market analysts believe interest rates will stay low or could go even lower over the coming months. surprisingly, nearly half of consumers don't comparison shop for the best possible loan rate. >> you should shop. if you're shopping for shoes, you should definitely shop for something that's your single largest investment. >> reporter: advice from experts, it's better to re-fi now than to hope rates will go lower. >>> back in a moment, as promised, with a big secret a lot of partners ha