421-a was a New York State property tax program that encouraged the construction of new multifamily housing in NYC through property tax exemptions. The 421-a program provided eligible residential development with partial property tax exemptions for a specified period in exchange for providing affordable housing requirements. 421-a became one of NYC’s primary methods of promoting new affordable housing development. 421-a expired in 2022 and was subsequently replaced by a stricter 485-x program, which established new requirements for projects seeking similar property tax benefits. The 421-a program is no longer available to new developments and is referenced primarily as the predecessor to 485-x. (New York Real Property Tax Law 421-a, New York State Senate, Verified June 2026)