Learn NYC property · Deeds, mortgages and sales

Comparable sales: how professionals use them, and how BlockLot picks them

What comparable sales are, how appraisers and assessors choose and adjust them, the units they compare on — price per square foot, per unit — and, as our own reading of the public record, how BlockLot picks a building's comparable sales and when it declines to estimate a value.

Comparable sales — comps — are recent sales of properties like the one being valued, used as evidence of what it would sell for. A comparable sale is similar enough to the subject, in place, size, age and kind, that its price, adjusted for the differences, says something about the subject's market value. Comparing sales is how most people answer what is this worth? — the State's guide for homeowners calls it the primary method of professional appraisers and real estate agents.

How professionals use them

Appraisers and assessors recognize three ways to value a property: the sales comparison approach, the income approach and the cost approach. New York's assessment standards call comparable sales the preferred approach for homes and vacant land, whenever there are enough sales; for income-producing property — an apartment or office building bought for its rents — the income approach comes first.

A professional picks comps in four steps:

1. Recent sales. The federal housing agency's appraisal handbook prefers sales from the last six months and requires at least three from the last twelve. In a slow market, older sales may be used with an explanation, adjusted for the time that has passed.
2. Similar properties nearby. Comps are chosen for location and physical likeness — size, age, style, quality, condition — never for their price. The handbook warns against choosing sales because they bracket a hoped-for value. In a condominium, recent resales of other units in the same building are often the best evidence there is.
3. Arm's-length sales only. A sale between relatives, out of an estate, or at a foreclosure auction does not show market value; see sale prices.
4. Adjustments. No comp matches exactly, so each price is adjusted for the differences: a comp that is better than the subject in some way is adjusted down, one that is worse is adjusted up. The State's guide for homeowners works an example: add $30,000 to a comp in a less desirable location, subtract $12,000 for its extra bathroom. Prices are also adjusted for time — at half a percent a month, a sale sixteen months old is adjusted up 8%.

Units of comparison

Houses and condo apartments are compared whole, by price. Larger buildings rarely sell often enough for that, so their prices are put on a common scale: price per square foot of floor area, or price per unit — per apartment. Each has a weakness. Price per unit misleads when the apartments differ in size — studios against three-bedrooms — and price per square foot still needs adjusting for the mix and the condition.

How the City uses comparable sales

The Department of Finance values one- to three-family homes from the sales of similar properties nearby over the last three years — the comparable sales method of its market value. State law requires co-ops and condominiums to be valued as if they were rental buildings, so for them DOF compares rents, not sales: it values each from the incomes and expenses of similar rental buildings.

How BlockLot picks them — our reading

A building's page in BlockLot shows comparable sales and, when it can, an implied value. Both are our own reading of the public record, made by rules we publish here, not an appraisal.

What counts as a comp. A deed recorded in ACRIS with a price from $250,000 to $30 million, conveying one lot and the whole interest, no older than three years. Deeds with no price, a nominal price or a partial interest are not sales at market value, and a deed that conveyed several lots has no price for any one of them. Narrowed by those rules, a year of deeds shrinks like this:

By BlockLot Intelligence's count, of the 57,985 deeds recorded in the twelve months to September 30, 2026, 29,168 — 50.3% — passed every rule. A price that repeats on more than two lots in one peer set is dropped as part of a package.

Where the peer set comes from. BlockLot looks for at least four comps in the closest peer set it can, widening one step at a time:

The census tract — a neighborhood-sized area the Census Bureau draws — is used rather than a radius, because a circle crosses parks, highways and zoning lines. Time widens before geography: a three-year-old sale next door is still next door, while a sale this month a mile away is a different market. Past the tract and three years, the ladder stops.

The implied value. From the peer set, BlockLot takes the median: the median price for a house or a condo unit; the median price per square foot for other buildings; per apartment only where a "unit" is a home. It qualifies or withholds the number in four cases, and says why:

• Too few comps — fewer than four in the widest peer set: the sales are listed, but no value is estimated.
• A recent sale of the building itself — a qualifying sale of the whole building, at arm's length, in the last 18 months is the market's answer, so it is shown instead.
• Methods that disagree — when the price per square foot and the price per unit differ more than twofold, a range is shown, never one figure.
• A wider peer set is named above the figure whenever it did not come from the same block.

It knows nothing about a building's condition, renovation, floor, light or leases, so it is a starting point for a question — is this owner holding more than they think? — not a price for a deal.

Where you see this in BlockLot

A building's Comparable sales card lists the peer set, its median price per square foot or per unit, and the implied value or the reason there is none; an area's page runs the same engine for each kind of building in it.

Questions people ask

How many comparable sales do you need? Appraisers generally use at least three; the State's guide for homeowners says the same. BlockLot requires four before it estimates a value.

How recent must a comparable sale be? As recent as possible: the federal appraisal handbook prefers six months and requires three sales within twelve. BlockLot looks back 18 months first, and at most three years.

Why are foreclosures and family sales excluded? Because they are not arm's-length: the price reflects pressure or a relationship, not the open market.

Is BlockLot's implied value an appraisal? No. It is a median of public sale prices, with no adjustment for condition or features. An appraisal is a licensed appraiser's opinion of value, made with an inspection and adjustments.

How does the City use comparable sales for my tax? For a one- to three-family home, DOF estimates market value from similar sales nearby over three years. Co-ops and condos are valued as rental buildings instead, by law.

Related

• Sale prices in the public record: ACRIS, DOF's sales files, $0 deeds and package deals — Where New York City sale prices are published — the price written on the deed in ACRIS and the Department of Finance's rolling and annualized sales files — why so many sales show $0, and how partial interests, package deals and non-arm's-length sales distort a price.
• Market value (NYC property tax) — What the Department of Finance's "market value" is, why it is not what a property would sell for, how DOF estimates it for each tax class — with the income formula — and how and when an owner can challenge it.
• Deeds in New York City: the kinds of deed, and grantor and grantee — What a deed is, the kinds New York law describes — bargain and sale, quitclaim, executor's, referee's — transfer-on-death and life estate deeds, who the grantor and grantee are, and what party 1 and party 2 mean on any document in ACRIS.
• BlockLot Intelligence: how our figures are made — Where the live counts and timeframes in BlockLot's guides come from — the public records they are computed from, how often they are refreshed, how a waiting time is measured, and what the numbers can and cannot tell you.
• 311, community districts and the map units a property sits in — What 311 is and what happens to a building complaint made to it, and the map units every New York City lot is filed under — community districts and boards, City Council districts, census tracts and Neighborhood Tabulation Areas.

Sources

• BlockLot Intelligence — BlockLot's own analysis of the public records below, computed October 10, 2026.
  • ACRIS Real Property Master
  • ACRIS Real Property Legals
  • ACRIS Real Property Parties
• NYS Office of Real Property Tax Services — Valuation standards
• NYS Office of Real Property Tax Services — Glossary
• NYS Office of Real Property Tax Services — How to estimate the market value of your home
• NYS Office of Real Property Tax Services — Sales usability criteria
• NYS Office of Real Property Tax Services — Level of assessment, an owner's manual
• HUD — Single Family Housing Policy Handbook 4000.1 (appraisal: the sales comparison approach)
• HUD — Handbook 4465.1, chapter 8: the market comparison approach (historical)
• DOF — Determining your market value
• DOF — Definitions of property assessment terms
• DOF — Cooperative and condominium comparables
• New York Real Property Tax Law § 581

By BlockLot. Reviewed October 9, 2026. Figures by BlockLot Intelligence, computed from public data on October 10, 2026. This page explains the rules in general; it is not legal or tax advice. For a decision about a specific property, check the official source or ask a professional. Spotted a mistake? Tell us.