The housing market is heating back up. But only a small percentage of new homes are fully-built.

• New-home sales jumped 8% in December as mortgage rates fell.
• But most of the new homes aren't yet complete, with only 17.9% ready for move-in.

New-home sales rebounded in December, rising 8% as homebuyers rushed to take advantage of falling mortgage rates, US Census Bureau data shows.

But while consumers appear eager to re-engage with the housing market, new purchases don't mean an immediate move-in for some.

Realtor.com reports that only 17.9% of for-sale new homes were completed in December as homebuilders race to catch up with supply needs. Meanwhile, 58.5% of new homes are still under construction, while 23.6% have yet to even be started. Despite this, homebuyers are jumping at what's available to buy, which caused new home inventory to fall below November's levels.

Sidelined buyers jumped back into the market as the 30-year fixed mortgage rate descended to a six-month low in December, now averaging 6.32%. This decline from 8% peak levels in October was spurred by bets that the Federal Reserve would start cutting interest rates.

Total for-sale inventory, which includes existing homes, rose 4.9% year-over-year. Of that, new homes took on a bigger share of the inventory, as high mortgage rates kept homeowners from selling.

"New home sales ended the year on a high note thanks largely to falling interest rates and a decline in existing home sales," the National Association of Homebuilders' Danushka Nanayakkara-Skillington said in a press release. But she also outlined further challenges, such as a lack of lots and skilled labor.

Still, NAHB's CEO Jim Tobin separately expects construction and demand to take off in 2024, once consumers realize ultra-low mortgage rates aren't coming back.