More Boston homes were listed for sale in January compared to the previous month, according to a new report.

Nationwide, January marked the first time in 18 months that more homes were listed for sale compared to the previous month, with an additional 15,000 homes, or a 2.9 percent increase, listed for sale compared to December, according to a new report by national real estate brokerage ZipRealty.

In the Boston metro area, 27,547 MLS-listed single-family homes and condos were listed for sale in January, a 4.8 percent increase from the previous month. However, single-family homes and condos listed for sale in the area were down 9.8 percent year-over-year.

Markets in California showed significant jumps in inventory in January with month-over-month increases of 10.1 percent in the San Francisco Bay Area, 8 percent in Orange County, 4.5 percent in Los Angeles, and 6.5 percent in San Diego.

Baltimore was one of only two markets where the number of homes listed for sale decreased, at a modest 1.9 percent. In Miami, ZipRealty tracked a minor decrease of .05 percent.

"Serious sellers need to list their home now, rather than wait for the spring, to capitalize on buyers looking to take advantage of the tax credit extension," said ZipRealty President and CEO Patrick Lashinsky. "While the number of homes for sale is starting to increase, we are still seeing some markets with a shortage of homes for sale."