421-a

The 421-a program exempted new multifamily construction from the property taxes its added value would otherwise incur, phasing into full taxation over the benefit term. Across its eras the bargain's conditions grew — affordability shares, rent regulation of covered units during benefit periods, wage requirements in later versions — making the program both the engine of market-rate development economics and a recurring political battleground.

It lapsed for new entrants and was succeeded by 485-x; projects vested under prior eras continue under their era's terms. In records, an active 421-a benefit explains a building's tax bill and implies its era's obligations — regulation included — while the expiration schedule is a scheduled repricing of both taxes and, sometimes, tenancies.