“The concept on paper is to increase affordability for a buyer,” said Jonathan J. Miller, the president of Miller Samuel Real Estate Appraisers & Consultants. “But it doesn’t factor in human behavior.”

Even though an owner’s tax bill from the city shows the abated and unabated tax amounts, owners tend to overestimate their income growth and underestimate future tax assessments, Mr. Miller said. It’s hard for condo owners to anticipate how much their total tax bills will grow over time because the city could increase their property assessment annually.

Initial prices in abated buildings also tended to be higher, because the landowner would charge the developer a premium for property that qualified for the abatement program, and the developer would pass that cost onto buyers, he said. (Some developers also took advantage of 421-a exemptions when building rentals, but the expiration of those abatements has less impact on renters.)

Many bought tax-abated units at prices that they justified with low monthly carrying costs, or plans to rent the units before higher taxes kicked in. The sticker shock at the end of abatement is twofold: The share of the total tax responsibility steadily rises as the abatement drops over time, while the overall tax bill often climbs when the city reassesses the property. Sellers in buildings with expired abatements are also often competing with owners in similar circumstances, sometimes in the same buildings, which can push sale prices down further, Mr. Miller said.

New York is also in one of the toughest markets for sellers in years, said Lindsay Barton Barrett, an agent with Douglas Elliman.

“People are sensitive to everything now,” Ms. Barrett said of buyers, who have ample choice and might be leery of buying a unit that used to have much lower carrying costs, even though the taxes may now be similar to what they would pay at comparable unabated buildings.