More than one in four U.S. homeowners—or 27%—don’t know the interest rate on their current home, according to a new study published by Bankrate. That lack of knowledge may be prompting homeowners to miss out on refinancing their mortgage into a lower rate and saving on monthly costs. Mortgage rates have recently been hovering at three-year lows.

Younger homeowners are the most likely to be unaware of their mortgage rate. About 34% of homeowners between the ages of 29 to 39 say they’re unsure what their mortgage rate is. On the other hand, for comparison, 23% of homeowners between the ages of 56 and 74 don’t know their mortgage rate.

“It is concerning that more than a quarter of mortgage borrowers don’t know the rate of interest they’re paying on their existing mortgage,” says Mark Hamrick, Bankrate’s senior economist analyst. “Given the decline in mortgage rates we’ve seen over the past year, many qualified homeowners would stand to benefit, or save, by refinancing.”

For example, Fox Business offers the following example of how big a difference it can make: A $200,000 mortgage with a 4.70% interest rate could cost a homeowner about $119 a month more in interest than a mortgage with a 4.13% rate.

But mortgage rates are a lot cheaper now. The 30-year fixed-rate mortgage averaged 3.47% last week, according to Freddie Mac.

More than 11 million homeowners could save an average of $268 per month on their mortgages by refinancing, according to a recent report by Black Knight.