Interest rates have surged in the opening weeks of 2018, raising uncomfortable questions about how much higher they can go before home purchases become unaffordable.

But there’s one area of the housing market where the impact is already being felt. Approximately 1.4 million Americans lost the interest rate incentive to refinance their mortgages in the first six weeks of 2018, according to an analysis from real estate data provider Black Knight.

The benchmark 30-year fixed-rate mortgage averaged 4.43% during the week ending March 1, according to Freddie Mac’s weekly survey. That was up three basis points from the prior week and leaves rates nearly half-a-percentage point higher than the level at which they started the year.

Whether or not a refinance makes sense depends on a lot more than just being able to seize a lower interest rate. Borrowers have to have enough equity in the home, and appear creditworthy—to have a job and have been paying the existing mortgage faithfully, in other words.

That’s why as recently…