The 421-a Tax Abatement: What It Is, Where to Find It, and What Happens When It Expires

421-a is a NYC property tax abatement designed to incentivize new residential construction. For buyers, it's a meaningful benefit — but only for as long as it lasts, which is usually 10, 15, 20, or 25 years from when the building was completed. When 421-a phases out and expires, the building's property tax bill jumps to the full unabated amount, often 3 to 5x what owners had been paying. If you're buying a new condo, you need to know two numbers: how much the abatement is currently saving you, and what the tax bill will look like the year after it ends.

How 421-a actually works

When a developer builds new residential housing in NYC, the city assesses property tax on the building's market value. That tax bill, applied at NYC's typical condo tax rates, would make most new construction completely uneconomic for buyers. 421-a was created to bridge that gap. The developer applies for the abatement, and if approved, the building's units pay tax on a heavily reduced assessed value — sometimes nearly zero in early years — for a fixed number of years (10, 15, 20, or 25 depending on the program version and affordability commitment). The abatement then phases out: the taxable portion of assessed value gradually rises from say 25% in year 1 to 100% in the final year. Once expired, you pay the full tax bill on the full assessed value. For buyers, this means: while the abatement is in place, monthly carrying costs can be 30 to 50% lower than they will be once it ends. If you're buying a unit with a 421-a in place, model the post-expiration tax bill carefully. The right way: ask the offering plan or the listing agent for the year-by-year projected tax bill through expiration, plus the year-after-expiration projected bill. If they can't give you that, get your attorney to compute it from the building's current assessed value and the relevant property tax class rate.

A worked example, and what to do

Imagine a $2M condo in a 25-year 421-a building completed in 2018. Today, year 8 of the abatement, the unit pays roughly $400 per month in property tax — call it $4,800 per year. Once the abatement fully expires in 2043, the unit's projected unabated tax could easily run $24,000 to $30,000 per year, or $2,000 to $2,500 per month. That's a $1,500 to $2,000 monthly carrying-cost jump that hits every owner in the building on the same day. Smart buyers do three things. First, they price that future expense into their bid — a unit with 5 years left on a 25-year abatement is structurally less valuable than the same unit with 25 years left, and the listing price should reflect that (often it doesn't). Second, they save the difference. If you're saving $1,500 a month vs. the unabated bill, set that aside in an escrow you mentally label "future tax bill," not in your spending budget. Third, they don't refinance based on the abated cost basis. If you stretch your loan to the carrying cost cap during the abatement, the post-expiration cliff can force a sale. What to do as a buyer: ask for the year-by-year tax projection through expiration plus year +1, model the post-expiration scenario into your decision, and don't trust generic listings that just quote "low taxes" without a date.

If you're considering a 421-a building and want me to pull the year-by-year tax projection for the specific unit and run the post-expiration math, that's a 15-minute call. 646.939.7375.