Multifamily Tax Abatement Underwriting: The Burn-Off

Published October 22, 2026

A capped 35-year 421-a building that holds the program minimum of 25% affordable units does not phase out of its exemption. Per the New York City Department of Finance benefit schedules summarized by MGNY Consulting, the capped version of the 421-a(16) benefit runs fully exempt through year 25, then in years 26 through 35 the exemption equals the share of affordable units — so a building at the minimum steps from a full exemption to roughly a quarter of one in a single tax year. The rent restrictions on those units do not step down with it.

That asymmetry is the whole problem with multifamily tax abatement underwriting. The abated tax line is the number the seller shows in the trailing 12 months. The restricted rent is the number that survives the exemption. A model that carries the first and forgets the second is pricing a cash flow with a known expiration date at a market multiple.

For capped 421-a(16) buildings, that step is not happening yet. The program, also called Affordable New York, covers projects that started construction from 2016 through mid-2022, so the earliest buildings reach year 26 in the early 2040s, and later completions well after that. It matters now for a different reason: a 10-year hold or a long-dated loan written today exits into a market whose buyers are likely to be underwriting that step, and the residual value is where it shows up first. The phase-outs landing on tax bills in 2026 belong to older 421-a(1-15) buildings working through their final benefit years.

Why Multifamily Tax Abatement Underwriting Breaks at the Reset

The mechanics are unusual among operating lines. Most expenses drift — insurance reprices annually, payroll moves with the labor market, utilities track consumption and tariff. The exemption benefit is different: it is a scheduled, dated, legally fixed event sitting on the property, and its size is knowable years ahead from the exemption filing.

Which makes the common failure a modeling choice rather than an information problem. A five-year or seven-year hold that begins in year 20 of a 25-year benefit — the position many 421-a(1-15) buildings are in today — runs the burn-off straight through the exit, and the buyer at that exit is underwriting a tax line that may be several times the one in the trailing statements. This is the same year-two discipline that property tax reset underwriting applies to the reassessment on sale, extended to a second, slower trigger with a known date.

The second half of the problem is that the exemption and the restriction run on different clocks. Per the New York City Department of Housing Preservation and Development, 485-x affordable housing units are permanently affordable and restricted units are permanently rent stabilized, while the exemption terms are 35 years for the large and modest rental options, 40 years for very large projects in the designated zones, and 10 years for the small rental option. A building can therefore reach a point where it pays full taxes on units it can never fully reprice.

What the Programs Actually Say

Sourced facts first; the reading of them follows in the next section.

• Per the New York City Department of Housing Preservation and Development, 485-x Option A requires 25% of units as affordable housing units averaging 80% of Area Median Income (AMI) for rentals of 100 or more units, or averaging 60% of AMI for projects of 150 or more units in Zones A and B; Option B requires 20% of units averaging 80% of AMI for buildings of 6 to 99 units.
• Per the same source, the highest income band permitted in those structures is capped at 100% of AMI, and all affordable housing units are described as permanently affordable.
• Per the New York City Department of Finance benefit schedules summarized by MGNY Consulting, the 421-a(1-15) 25-year benefit is fully exempt in years 1 through 21 and phases out at 80%, 60%, 40%, and 20% across years 22 through 25; the uncapped 421-a(16) 35-year benefit has no phase-out and simply ends; the capped version drops in year 26 to the affordable share.
• Per the NYU Furman Center's 2024 brief "Principles to Guide an Improved Tax Exemption to Secure New Rental Housing" (corrected version dated April 12, 2024), its feasibility model sets full property taxes at 25% of gross revenue for New York City rental prototypes, a rule of thumb the authors describe as at the low end of what the industry uses. The brief adds that a cross-check using the Department of Finance's valuation method produced a result above 25% of gross revenue in every case, and it reports that 123,500 new units were built using various forms of 421-a between 2010 and 2020.
• Per Texas House Bill 21, effective May 28, 2025, and summaries published by BakerHostetler and Chapman and Cutler, housing finance corporation properties must meet one of two affordability tiers — 10% of units at 60% of AMI plus 40% at 80% of AMI, or 10% at 50% of AMI plus 40% at 100% of AMI — with annual compliance audits submitted to the Texas Department of Housing and Community Affairs.
• Per the Federal Reserve H.15 release (as republished in the FRED DGS10 series), the 10-year Treasury constant maturity yield was 5.15% on October 19, 2026.

Read as interpretation rather than prediction: the combination of a dated exemption step and a permanent rent restriction compresses where value can come from. Rent growth that would normally absorb a rising tax line is unavailable on the restricted units by design, so the burn-off lands disproportionately on the market-rate share. Program terms vary by jurisdiction and vintage, and the figures above are national and program-level references rather than a read on any specific asset.

What the Step Costs: A Worked Example

Illustrative figures throughout. A 150-unit rental building carrying a capped 421-a(16) benefit at the 25% affordable minimum, with benefit year 1 in 2019 — so year 26, and the step, arrives around 2044. The question is how that step looks to a buyer underwriting the building in its early 2040s, or to anyone today pricing a residual or a long-dated refinance against it. Effective Gross Income (EGI) of roughly $6.0M, held flat in both columns so the tax change is isolated. Operating expenses excluding real estate taxes of approximately $2.1M. Abated real estate taxes of about $150,000, reflecting the pre-improvement assessment.

Full taxes are modeled at approximately 25% of gross revenue, the rule of thumb in the NYU Furman Center's 2024 brief — roughly $1.5M here. In year 26 the exemption falls to the 25% affordable share, so about 75% of the roughly $1.35M benefit is lost, adding on the order of $1.0M to the tax line.

The value step is roughly $20M, or about 27% of the abated-basis valuation, on a property where nothing operational has changed. The coverage step matters more immediately: debt sized at a 50% Loan-to-Value (LTV) ratio against the abated Net Operating Income (NOI), at a 6.5% rate on 30-year amortization, carries annual debt service of approximately $2.84M. That is a Debt Service Coverage Ratio (DSCR) near 1.32x before the step and under 1.0x after it. The sensitivity runs one way: at 30% of gross revenue, full taxes are about $1.8M, the lost benefit is about $1.24M, Net Operating Income falls to roughly $2.51M, value at a 5.0% cap rate to about $50M, and coverage to about 0.88x. Because the Furman cross-check came in above 25% in every case, the step shown in the table is more likely understated than overstated. Rate quotes and amortization terms change daily — verify current pricing directly with a lender.

The line item most often missed is not the tax number itself but the assessment underneath it. The abated years are assessed on a pre-improvement basis, so the full-tax figure is not the current bill grossed up — it is a new assessment on a completed, stabilized building, and that figure may not exist anywhere in the seller's statements. The mechanics of carrying it through to the bottom line are the standard Net Operating Income build, and its effect on sizing runs through debt service coverage; the step is simply larger than most expense surprises.

Texas Moved the Trigger to the Transaction

The New York programs attach their step to a calendar date. Texas House Bill 21 attached part of its reset to the deal itself. Per the BakerHostetler and Chapman and Cutler summaries of the statute, the revised affordability restrictions apply to existing housing finance corporation properties by the earlier of December 31, 2035 or the first sale or refinancing of the property — which means a buyer or a refinancing sponsor may be the event that brings the new tiers into force, rather than inheriting the prior structure.

A second dated item sits closer. Properties held outside the sponsoring local government's jurisdiction need approval from the city or county and any local housing finance corporation by December 31, 2026, or the exemption may be lost on January 1, 2027. For anything trading or refinancing into that window, the approval status is a diligence item with a hard date attached, and the annual compliance audit filed with the Texas Department of Housing and Community Affairs is where the operating record either supports the exemption or does not. These details are subject to change — verify current terms directly with counsel and the sponsoring issuer.

Where This Analysis Breaks

The strongest counter-argument is that the market already prices this. A building sitting three years from a known exemption cliff does not trade at the same cap rate as an unencumbered asset, and buyers in New York City routinely underwrite to a stabilized post-burn-off tax load. If pricing already reflects the step, then modeling it again as a surprise overstates the risk and could lead to passing on assets that are fairly priced.

That objection holds where the remaining term is short and visible. It holds less well at a 15-year or 20-year remaining term, where discounting the step to present value makes it look small and where the exit assumption quietly carries it instead. The exit is where the compounding shows up: a residual priced off pre-burn-off income assumes the next buyer accepts the same treatment, which is the same residual-assumption fragility that disciplined exit pricing and an occupancy-first revenue model try to surface elsewhere in the model.

There is also real uncertainty in the full-tax figure. The 25%-of-gross-revenue assumption used above is a rule of thumb from one brief, not a bill from an assessor, and actual assessment practice, equalization ratios, class shares, and the availability of a successor exemption all move it. A certiorari filing can reduce the stepped-up assessment, sometimes materially. Treating the modeled number as precise would be its own error — the defensible version is probably a range, carried as a scenario rather than a point estimate, with the governing exemption agreement read in full before any of it is relied on.

Finally, the permanence of affordability cuts both ways. A permanently restricted unit is a permanently capped revenue line, but it also tends to be a highly occupied one, with a waiting list and low turnover cost, and agency lenders have shown appetite for mission-qualifying collateral. The restricted units are not purely a drag; they simply stop paying for the tax relief once the relief ends.

The Underwriting Takeaway

Multifamily tax abatement underwriting comes down to putting two dates in the model: when the exemption steps, and when the restriction ends. In several current programs the second date does not exist, because the restriction is permanent. A hold period that spans the first date without repricing the tax line is carrying income with a known expiration at a market multiple.

The practical test is small. Pull the exemption filing, find the benefit year the property is actually in, model the stepped tax load as a range rather than a point, and look at what the Debt Service Coverage Ratio does on the far side of it. A deal that only clears coverage on the abated basis is a deal whose financeability depends on a benefit that is scheduled to end.

UWmatic is an AI-powered underwriting platform built for multifamily and mobile home park investors. Model the abatement step as a dated event and see what it does to Net Operating Income, coverage, and exit value across the hold. Try the free underwriting calculator →

This analysis reflects current market interpretations as of the publication date and may evolve as new data becomes available. Figures cited are drawn from public sources including the New York City Department of Housing Preservation and Development, New York City Department of Finance benefit schedules as summarized by MGNY Consulting, the NYU Furman Center's 2024 rental housing tax exemption brief, Texas House Bill 21 and published summaries by BakerHostetler and Chapman and Cutler, and the Federal Reserve H.15 release via FRED, and are subject to revision. Nothing in this post is investment advice; readers should conduct their own diligence and consult qualified professionals before making investment decisions.