A new report from Streeteasy reinforces a dispiriting reality that many New Yorkers already know: The path to buying a home in the city is hard because home prices are so high in relation to incomes. In a back-of-the-envelope calculation, the real estate listings firm estimates that New Yorkers looking to buy their first home would have to accumulate savings over an average of 18 years—nearly 11 years longer than the national average—to buy a median priced home in the city.

Streeteasy based the calculation on the $70,406 median household income of New Yorkers ages 25 to 44 in 2017, assuming a savings rate of 10 percent of gross annual income and a customary 20 percent down payment.

The current national housing savings rate is 7.6 percent of income after taxes. Other studies have shown that 25- to 44-year-olds save at much lower rates than that, suggesting that the actual average time needed to save for a down payment is even longer.

The median price of a home sold in New York City is $637,250—three times higher than the rest of the country, according to the report. A 2016 study by the NYU’s Furman Center found that while housing sale prices rose nearly 200 percent between 1990 and 2014, real median household income fell by 11 percent.

The barriers explain why New York is a city of renters, about 67 percent, according to U.S. census figures.

Buyers who are not independently wealthy often rely on help from family, a well-observed phenomenon among real estate brokers. “It’s almost like a GoFundMe,” Jason Haber, a broker at Warburg Realty, told the New York Times last week in a story about first-time home buyers. (For those without rich relatives, affording a home purchase may require renting a cheap room for years and avoiding having a social life.)

Other reports have examined the weak rate of homeownership in New York City and its socioeconomic underpinnings. The Furman Center study that found only 26 percent of black and 15 percent of Hispanic households owned their homes, compared to 42 percent of white households and 39 percent of Asian households, according to 2014 data.

The Streeteasy report comes amid slumping housing sales in Manhattan and Brooklyn. In Manhattan, the number of closed co-op and condo sales in the fourth quarter of 2018 fell by 3.3 percent over the same period last year, according to the real estate brokerage Elliman. In Brooklyn, closed sales fell by 5.8 percent.

Real estate appraiser Jonathan Miller characterized the market as one in which New Yorkers are basically “camping out” in the rental market.

Nancy Wu, the author of the Streeteasy report, said the slow sales market means buyers have more room to negotiate. “First time homebuyers should definitely think about which neighborhoods they want to look into,” she said. “In all three boroughs, Manhattan, Brooklyn, and Queens, prices have been falling and inventory has been growing.”

In other words, home buyers could see some potential bargains—if they can afford a down payment at all.