Guide · Sources reviewed September 20, 2026

Choosing comparable sales for a Nassau County grievance

Choose sales of homes similar in size, type, location, and condition. Record the differences and compare matching periods; a lower neighboring tax bill alone is not evidence.

What you are actually arguing

Nassau County defines market value as “the most probable price at which a property would sell if offered for sale under ordinary circumstances.” A comparable sale is useful to the extent it stands in for that: a real transaction, close enough to your home in the ways that drive price, that a reader can accept it as a proxy.

Note the phrase ordinary circumstances. A sale between relatives, an estate sale, or a foreclosure may be a real transaction and still be a poor comparable.

Start with the differences that move price

When you line a sale up against your home, work through these in order:

1. Property type and style. Compare like with like before anything else.
2. Living area. Usually the single largest driver. A meaningful size gap is hard to argue past.
3. Location. Same school district and same neighborhood, ideally. Proximity on a map is not the same as comparability. Our area pages show the range of values across each school district and village.
4. Age and condition. Often the weakest data you will have, and the most likely to be challenged.
5. Sale date. A recent sale reflects the market you are arguing about; an older one may not.
6. Lot and setting. Lot size, corner or through lots, and obvious external factors.

Write down what does not match

The instinct is to present only flattering sales. Resist it. A comparison you have annotated honestly (“larger by roughly 300 square feet, sold fourteen months ago, renovated kitchen per the listing”) is more persuasive than an unqualified list, and it prepares you for the obvious questions.

Keep a short record for each sale: the address, the sale date and price, where you found it, and the two or three differences from your home. If condition or renovation history is unknown, write that it is unknown. An open question is a legitimate entry; an assumption presented as a fact is not.

A neighbor’s lower tax bill is not a comparable

This is the most common mistake, and it is worth stating plainly. Different exemptions and different taxing districts produce different bills for similar homes, so a bill comparison does not establish that your assessment is wrong. Our exemptions guide explains why two neighbors can be taxed differently on purpose.

The same caution applies to assessed values pulled from different years. Compare matching periods and matching measures, and label both.

Which sales count

Only sold homes are comparables. A neighbor’s lower assessment is not evidence of value unless that home sold. Practitioners suggest:

• Sales from about the last two years. Your own home’s sale can be older and still count.
• Ordinary sales only. Leave out foreclosures, short sales, sales between relatives, and homes sold damaged.
• Five sales, starting with the first five ARC’s online system suggests. They are usually nearby and similar, and using them shows you did not cherry-pick. Swap one out only for a clearly closer match.

If the only close matches are old or imperfect, say so rather than hiding it.

Compare sales at the County’s level, not with your County value

Nassau County’s recent rolls value most homes well below what they sell for: across school districts, homes that sold were valued at roughly 50% to 66% of their price. So a sale price above your County value does not mean you are fairly assessed. Divide your County value by your district’s level, shown on its area page, to get the price it stands for. If good sales come in below that, you have a case. Our property pages do this arithmetic for you.

Using the Good Grieves checker

Our property checker brings available County assessment records, property details, and sales context into one view so you can start this comparison from records rather than from memory. Coverage varies, and a missing record is not a zero. Check the year and source labels, and verify anything important with the County.

The checker shows available records; it does not perform an appraisal, and it does not decide which sales are comparable. That judgment stays with you, or with a professional you engage.

Then put it on the calendar

Evidence is only useful inside the filing window. Read the deadline guide for the published dates and the process guide for what follows a filing. Savings are not guaranteed, and this page is general information rather than an appraisal or legal advice.