The average monthly mortgage payment in the U.S. in December soared 21.6% from a year ago, the biggest increase since real-estate services company Redfin Corp. /zigman2/quotes/203726414/composite RDFN -1.25% has been keeping records, and are expected to keep rising this year, Redfin said Friday. And monthly average rents in December jumped 14.1% to $1,877, also the biggest increase on record. Redfin attributed the rise in mortgage payments to both climbing home prices and mortgage rates. Redfin started recording rental data in February 2019. "And those rising mortgage costs push more potential homebuyers into renting instead, which pushed up demand and prices for rentals," said Redfin Chief Economist Daryl Fairweather. "Mortgage rate increases are accelerating, which will cause both mortgage payments and rent to grow throughout 2022." Redfin's stock, which fell 0.7% in premarket trading, has plunged 42.3% over the past three months to close Thursday at the lowest price since June 1, 2020, while the S&P 500 /zigman2/quotes/210599714/realtime SPX +1.55% has lost 1.5% over the same time.