NYC ADU Property Tax: What Changes When You Build

property taxes are one of the biggest questions homeowners have about building an ADU. will your taxes double? is there a way to reduce the impact? what happens when inspectors reassess your property?

the good news: NYC has put real tax protections in place for ADU construction, including a $200,000 property tax exemption for 5 years and built-in assessment caps that limit how fast your taxes can grow. the bad news: the system is complex, and the exemption doesn't last forever. here's everything you need to know.

the $200K ADU tax exemption

the most important thing to know: when you build a legal ADU in NYC, you're eligible for a property tax exemption of up to $200,000 in assessed value for 5 years. this is a specific provision that was included in the ADU legislation to encourage homeowners to build.

what this means in practice:

• the first $200,000 of increased assessed value from your ADU is exempt from property taxes for 5 years
• since most ADUs increase assessed value by $80K–$180K, many homeowners will pay zero additional property tax for the full 5-year period
• the exemption applies automatically once your ADU receives a certificate of occupancy and is registered with the Department of Finance

to put real numbers on this: if your current assessed value is $50,000 and your ADU increases it to $90,000, that $40,000 increase is fully covered by the exemption. your property tax bill stays the same for 5 years.

how NYC property tax assessment works

to understand the ADU tax impact, you need to understand how NYC property taxes work — because it's different from almost every other city in the country.

NYC has 4 property tax classes. most ADU-eligible homes fall into Class 1 (one- to three-family residential properties). class 1 properties get significant protections:

protection	limit	what it means
annual assessment increase cap	6% per year	your assessed value can't jump more than 6% in any single year
5-year assessment increase cap	20% over 5 years	even if your property value doubles, the assessment only rises 20% over 5 years
assessment ratio	6% of market value	only 6% of your home's market value is used for tax calculation

these caps are powerful. they mean that even after the 5-year ADU exemption expires, your taxes can't spike dramatically — they'll phase in gradually over years.

year-by-year tax impact example

let's walk through a realistic example for a homeowner in queens building a $200K backyard ADU:

before ADU:

• market value: $800,000
• assessed value: $48,000 (6% of market)
• annual property tax: ~$4,600

after ADU (with exemption active):

• market value: $950,000 (property appreciated ~$150K due to ADU)
• new assessed value: $57,000
• increase in assessed value: $9,000
• exemption covers: up to $200,000 — so the full $9,000 increase is exempt
• annual property tax: still ~$4,600 (no change)

years 1–5: no additional tax thanks to the exemption

years 6–10 (exemption expired):

• the $9,000 assessment increase phases in, subject to the 6%/year cap
• your tax bill increases by roughly $800–$1,200/year — phased in over several years
• but you're earning $24,000+/year in rental income, so the net impact is strongly positive

how to apply for the ADU tax exemption

the application process is through the NYC Department of Finance:

1. build your ADU and receive a certificate of occupancy from DOB
2. file for the exemption with the Department of Finance — this requires your CO, proof of owner-occupancy, and basic property information
3. the exemption takes effect on the next assessment roll (January tentative roll, July final roll)
4. maintain owner-occupancy — the exemption requires that you live in the primary dwelling. if you move out, the exemption ends.

important timing note: the Department of Finance updates assessments on an annual cycle. depending on when you complete your ADU, there may be a gap between completion and when the exemption appears on your bill. during this gap, you might see a temporary increase that gets corrected once the exemption is processed.

what triggers a reassessment

building an ADU will trigger a property reassessment. here's what the assessor looks at:

• the ADU itself — square footage, finishes, configuration
• the overall property — the assessor reassesses the entire property, not just the ADU
• comparable sales — they look at what similar properties with ADUs have sold for
• income approach — if you're renting the ADU, the rental income is a factor in valuation

the reassessment happens automatically when DOB issues a new certificate of occupancy. you don't need to request it — the Department of Finance gets notified by DOB.

property tax class considerations

one question homeowners ask: does adding an ADU change my property's tax class?

the answer: usually no. adding an ADU to a one- or two-family home keeps you in Class 1, which is the most favorable class. you'd only move to a different class if you converted from a 3-family to a 4+ family property — and the ADU rules are designed to prevent that scenario.

Class 1 benefits you want to keep:

• 6% assessment ratio (vs. 45% for Class 2 apartment buildings)
• 6%/year and 20%/5-year assessment caps
• lower effective tax rates

as long as your property remains a 1–3 family home (including the ADU), you stay in Class 1.

tax implications for rental income

beyond property taxes, there are income tax implications for ADU rental income:

• federal income tax — rental income is taxable. you report it on Schedule E.
• state and city income tax — NYC and NYS both tax rental income at your marginal rate.
• deductions — you can deduct mortgage interest (on the ADU portion), depreciation, repairs, insurance, property management fees, and a portion of utilities.
• depreciation — the ADU structure can be depreciated over 27.5 years. on a $200K build, that's approximately $7,270/year in depreciation deductions.

the depreciation deduction is particularly valuable. if you're earning $24,000/year in rent and deducting $7,270 in depreciation plus $3,000–$5,000 in other expenses, your taxable rental income drops to $12,000–$14,000.

we strongly recommend working with a tax professional who understands NYC real estate — the intersection of city, state, and federal tax rules is complex enough to justify professional guidance.

STAR exemption interaction

if you currently receive the STAR exemption (School Tax Relief), adding an ADU does not affect your STAR eligibility as long as you remain the owner-occupant of the primary dwelling. the ADU tax exemption and STAR exemption can stack — you get both.

however, if your income exceeds the Enhanced STAR threshold ($107,300 for 2025), you'll need to verify your eligibility annually through the Income Verification Program.

what happens if you sell

if you sell your property during the 5-year exemption period, the exemption transfers to the new owner for the remaining years — as long as the new owner is also an owner-occupant. this is a selling point: you can market the remaining tax exemption as a benefit to buyers.

for capital gains purposes, the ADU construction cost is added to your cost basis, which reduces your taxable gain when you sell. combined with the primary residence exclusion ($250K single / $500K married), most homeowners will have minimal capital gains tax impact.

the bottom line on taxes

the tax picture for NYC ADU construction is genuinely favorable:

• years 1–5: $200K exemption means most homeowners pay zero additional property tax
• years 6+: assessment caps limit increases to 6%/year, phasing in gradually
• rental income: taxable but heavily offset by depreciation and expense deductions
• net impact: even after full phase-in, the rental income ($18K–$30K/year) dramatically exceeds any tax increase ($800–$2,000/year)

taxes shouldn't be the reason you don't build an ADU. the math works overwhelmingly in your favor, especially during the 5-year exemption window. the sooner you build, the sooner you start that 5-year clock.

use the nycadu cost calculator to model your specific tax scenario, or check your property eligibility to get started.