Metro Atlanta home prices finished last year up 5.5 percent for the year, according to a closely watched national survey.

Atlanta’s 2015 price rise was slightly slower than the 5.7 percent gain for the top 20 metro areas in the S&P/Case-Shiller U.S. National Home Price Index.

Prices both in the Atlanta region and for all 20 metros were unchanged in December.

While the end of the year is usually slow, the latest number shows real estate is decelerating, said David Blitzer, chairman of the index committee at S&P Dow Jones.

“While home prices continue to rise, the pace is slowing a bit,” he said.

Svenja Gudell, chief economist at real estate research firm Zillow, said the market faces a range of concerns as the spring selling season approaches.

One is stubbornly low inventory — the number of homes for sale. There are economic undercurrents, too, from oil to global woes, Gudell said.

Among the largest metros, Atlanta’s annual price increase was tied with Charlotte’s for the 14th fastest. Hottest markets were Portland, where prices rose 11.2 percent, San Francisco, which scored an 10.3 percent rise, and Denver, where prices climbed 10.2 percent.

Smallest gains were in Washington, D.C., at 1.7 percent, and Chicago, at 2.4 percent.

In a separate report, Zillow said Atlanta led the nation in inventory gains for the year, at 6.8 percent. But it was one of only four metro areas with any gain at all, and local real estate experts say the stock in metro Atlanta remains well below historical norms.

For instance, inventory in January was still 51 percent lower than in early 2011, when the market started to emerge from the bust.

In a third report Tuesday, the National Association of Realtors said existing home sales crept up 0.4 percent in January, despite market volatility and economic worries. That followed a strong 2015, when sales reacher their highest level in nine years.

The median price was $213,800 in January, up 8.2 percent from a year earlier.

Driving those price increases are an absence of choices for buyers. The number of listings on the market nationally in January fell 2.2 percent from a year ago. At the current sales rate, the inventory of homes would be exhausted in four months. A balanced market usually contains six months’ supply.

Many homeowners are reluctant to sell, as they’re enjoying savings from low mortgage rates and lack enough equity to comfortably upgrade to another house.

“So far sales have been bulletproof to price increases, but this is unsustainable in a slowly growing economy unless inventory improves,” said Nela Richardson, chief economist at the real estate brokerage Redfin.

The affordability pressures are showing up in mortgage down payments. As a percentage of the purchase price, down payment levels fell slightly in the closing months of 2015, according to LendingTree, an online lender. But down payments increased in absolute terms to an average of $51,721 in the final three months of the year from $48,924 in the prior quarter.

— The Associated Press contributed to this article.