A home is most Americans’ single largest investment. The returns are losing ground.

Home prices nationally rose 1.5% in August compared with the same month last year, down from the 1.6% annual gain recorded in July, according to the S&P Cotality Case-Shiller U.S. National Home Price NSA Index.

While home prices aren’t yet falling, they’re weakening — rising at a slower pace than the current 3% rate of inflation. That means that housing wealth eroded in real terms for the fourth consecutive month, according to the index.

Home prices in nearly all of the metropolitan markets highlighted in the index fell month to month in August. Only Chicago saw price gains. Home prices are seasonal and usually drop this time of year, but this weakness was more significant than typical seasonal patterns.

Much of that is due to stubbornly high mortgage rates, which stagnated over the summer, when much of this index was measured. (The index is a 3-month running average). Rates have since declined, but not by a lot. The average rate on the 30-year fixed mortgage started June at just below 7% and fell to 6.5% by the end of August, according to Mortgage News Daily. It is now at 6.19%.

“Mortgage rates remaining above 6.5% continue to weigh on buyer demand, even during what should be the busy summer season. The combination of high financing costs and prices that remain near record highs has limited transaction activity,” wrote Nicholas Godec, head of fixed income tradables and commodities at S&P Dow Jones Indices, in a news release.

August prices rose the most in the New York metropolitan area, with a 6.1% annual gain, followed by Chicago at 5.9% and Cleveland at 4.7%. On the flip side, prices in Tampa fell 3.3% year over year, Phoenix dropped 1.7% and Miami declined 1.7%.

There was also weakness in the West, with prices in San Francisco down 1.5%, Denver down 0.7%, and San Diego down 0.7%. Seattle also turned very slightly negative.

“Markets that experienced the sharpest pandemic-era gains are now seeing the largest corrections, while more affordable metros with stable local economies are holding up better,” Godec said. “This adjustment may ultimately lead to a more sustainable market, but for now, homeowners are watching their real equity erode while buyers face the dual challenge of elevated prices and high borrowing costs.”

A separate survey from the Federal Housing Finance Agency (FHFA) that measures prices of homes with conforming loans showed house prices rose 2.3% in August year over year and 0.4% from July.

“This relative strength on a month-on-month basis reverses the recent weak trend and shows some stabilization in home prices across the US after several months of month-on-month declines,” said Eugenio Aleman, chief economist at Raymond James, in a statement. “We may see some more stability in home price appreciation during the rest of the year as the effects of lower mortgage interest rates support increased housing activity.”