The year begins with mortgage rates near historically low levels, with the 30-year fixed-rate mortgage averaging under 3%. Rates will remain low in January.

Today's mortgage rates sprouted from the pandemic and the resulting recession, in which millions of jobs withered.

Some lost jobs will return in 2021, but the economy is unlikely to flourish enough to push mortgage rates significantly higher in January, or indeed the first half of the year.

More than 6 million homeowners refinanced in the first nine months of 2020, and many millions more could save money by refinancing, according to Black Knight, a mortgage analytics company.

The average rate on a 30-year fixed-rate mortgage was around 4% APR at the beginning of 2020, and had fallen to around 3% in mid-December. At an interest rate of 4%, the monthly principal-and-interest payment on a 30-year fixed-rate mortgage for $200,000 is $954.83; at an interest rate of 3%, the payment is $843.21.

No wonder millions of people refinanced in 2020.

Because of lower rates, borrowed money goes further in 2021 than it went at the beginning of 2020. Here's the effect on buying power when the 30-year fixed mortgage rate drops from 4% to 3%:

At an interest rate of 4%, you can borrow $209,500 with a principal-and-interest payment of about $1,000 a month.; at 3%, you can borrow $237,200 with a principal-and-interest payment of about $1,000 a month, or $27,700 more.

Here are three caveats to this news:

1. Not enough homes are for sale to meet demand. Of homes sold in October, 72% were on the market less than a month, according to the National Association of Realtors. Because demand for homes exceeds supply, prices are going up fast.

2. Rising home prices have roughly kept pace with the increased loan affordability. The median price of an existing home went up 15.5% in the 12 months ending in October, NAR says. Meanwhile, the example above shows that borrowing power increased 13% with a 1 percentage point drop in the interest rate.

3. Millions of people are jobless. Without steady income, they are unable to qualify for mortgages.

2020 was a brutal year. Here's hoping that 2021's economic recovery brings good jobs to people who were laid off or endured reduced income. When people are ready to buy homes in 2021, low mortgage rates will await them.

Holden Lewis writes for NerdWallet. E-mail: Twitter: @HoldenL.