The condop, which sits on leased land and was the site of a fatal crane accident in 2008, was hindered by other issues, Mr. Lorber said, but buyers were deterred, in particular, by its relative remoteness. “If the building were built today,” he added, “it would sell right away.”

Measuring the precise effect of the subway construction on property values is difficult, because while the construction has caused a number of inconveniences (including the closing of parts of sidewalks and streets), it also coincided with a massive housing downturn. And this part of the Upper East Side has been falling out of favor for years, brokers say. But anecdotal evidence suggests that prices for co-ops and condominiums here dropped about 20 percent — a discount that is long gone, according to most brokers. Moreover, the prices of many apartments now reflect a subway bonus of about 10 percent, they say.

“The post-subway premium is already in effect,” said Itay Gamlieli, the owner of GZB Realty, who often works on the Upper East Side and lives there as well.

The modest blocks east of Third Avenue have long had lower prices than the fancier parts of the Upper East Side, known as the Silk Stocking District. But the new subway stations at East 72nd, East 86th and East 96th Streets, and the expanded one at East 63rd, seem to be having an equalizing effect on prices in what used to be more of a cotton socks district. (Initially, those stations will offer access to an extension of the Q line; later, they will service the T train as well.)

Consider the Kent, a 30-story, 83-unit brick, limestone and metal-paneled condo from the Extell Development Company rising at 200 East 95th Street, at Third Avenue. Prices for its spacious two- to five-bedroom apartments, which have up to 15-foot ceilings, marble-lined baths and Miele appliances, will start at about $2.4 million, or $2,500 a square foot, when sales begin in May, said Gary Barnett, Extell’s president.