Supply of homes for sale rises in SF, Bay Area — but how are prices holding up?

The biggest decline in the nine-county region was in Marin County, where the median sold price fell 10.9% to $1,560,000 from July to August, according to the Realtors group. In San Mateo County, prices fell 8.8% to a median $1,925,000, and in Contra Costa the decline was 5.4% with a median price of $889,500.

The median was relatively flat in San Francisco at $1,850,000, down just $2,500 from July. Sonoma was the only Bay Area county seeing an increase, with the median sold price rising 1.1% to $770,000 in August.

The price drops accompanied a small rise in supply: Available homes in the San Francisco metropolitan area listed on real estate website Zillow rose from 8,630 in July to 8,795 in August. The share of listings with a price cut grew as well — meaning that buyers had more choices and an improved chance of seeing a drop in asking price. However, compared to the same month in 2020, inventory was down 4.1%.

Zillow defines the San Francisco metro area as Alameda, Contra Costa, San Francisco, San Mateo and Marin counties.

According to the Realtors group, the unsold inventory index — indicating the number of months it would take to sell the supply of homes on the market at the current rate — was flat for most Bay Area counties in August.

Statewide, the median sold price set its fifth record in six months, reaching $827,940, up 2.1% from July and 17.1% from August last year, the Realtors group said.

Zillow uses a different metric called typical home value, which it calculates as an average of the middle third of the market, minus the top and bottom 5%. In August, the typical home value in the San Francisco metro area was $1,331,868, up 1.5% from July and 17.9% over last year, according to Zillow.

Nationwide, while home values grew in all 50 of the country’s largest markets last month, a deceleration is widespread, according to Zillow — 43 of the 50 major metros saw appreciation slow down. San Francisco was among the cities with the largest drop-off, along with Buffalo, San Diego and Austin.

The “lift of the gas pedal” in terms of home values “is indicative of balance returning to the market” Nicole Bachaud, economic data analyst at Zillow, said in a press release. But the factors that “pushed the market to extremes” this year are still present, she said.

Nationwide, home sales have been rising monthly since March, and monthly rent growth had been accelerating since January before slowing down slightly last month.

Typical rent in the San Francisco metro area in August — around $3,092 a month — was up from $3,072 in July and up 3.9% from $2,977 in August 2020, according to Zillow.

Danielle Echeverria is a San Francisco Chronicle staff writer. Email: danielle.echeverria@sfchronicle.com Twitter: @DanielleEchev