Mortgage rates are now at their highest level in four years and poised to move even higher. The timing couldn’t be worse, as the usually busy spring housing market kicked into gear early this year amid higher home prices and strong competition for a record low supply of homes for sale.

Add it all up, and affordability is starting to hurt.

The average rate on the popular 30-year fixed is now right around 4.50 percent, still low when looking historically, but buyers over the past six years have gotten more used to rates in the 3 percent range. Mortgage rates have not been at 5 percent since 2011.

A 5 percent rate would cause more than a quarter of today’s homebuyers to slow their plans, according to a Redfin survey of 4,000 consumers at the end of last year. Just 6 percent said they would drop their plans to buy altogether. About one-fifth of consumers said 5 percent rates would cause them to move with more urgency to purchase a home, fearing rates would rise even further. Another fifth said they would consider more affordable areas or just buy a smaller home.

Despite rate concerns, the bigger issue for buyers is changes to tax laws that had lowered the…