421-a expiration calculator

What happens to the taxes when a 421-a abatement expires?

A 421-a (or J-51) abatement exempts part of a building’s assessed value for a fixed benefit period — commonly 10 to 25 years, phasing out in steps. When it ends, the exempted value returns to the tax roll and bills can jump 3–5×. Type an address to see its abatements on record, the approximate expiration year, and the estimated bill after the benefit ends — computed from the city’s own exemption file.

Estimates use the current exempt value and FY2026 class rates; real 421-a benefits phase out gradually (typically 20% steps), so the full amount arrives over the final years rather than at once. Condo units are assessed individually — building-level lots show building-wide figures.

Buying in a 421-a building?

Ask for the abatement’s start date and schedule, not just “has 421-a.” A monthly payment that works today can rise by hundreds or thousands when the benefit ends — run the post-abatement tax through the mortgage calculator before you commit.