Homes in Seattle sold in an average of 47 days in 2017. That's the fastest it's ever been, according to a new analysis by Zillow.

It means something recent house hunters already have learned -- be ready to move fast when you find the home you want.

"As demand has outpaced supply in the housing market over the past three years, buying a home has become an exercise in speed and agility," said Zillow Senior Economist Aaron Terrazas in a statement.

The 47 day average in made Seattle the third-fastest market for selling homes in 2017. Only San Jose, Calif. (41 days) and San Francisco (43 days) were faster.

Zillow said May and June were the fastest-selling months in 2017. Homes stayed on the market for 42 days. That includes closing.

It's just going to get worse in 2018. Zillow predicts there will be 19.7 percent fewer homes on the market this year.

"This is shaping up to be another competitive home shopping season for buyers, who may have to linger on the market until they find the right home but then sprint across the finish line once they do," said Terrazas.

Be prepared to pay more than you planned. Zillow says 52.4 percent of homes in 2017 sold for more than the asking price.

Nationwide, it took 81 days for the typical U.S. home to sell in 2017. The slowest market for selling was New York City (134 days).