Assessment 101: What You Need to Know for Nassau County

It’s natural to be confused by the assessment process in Nassau County. While the County professes to make the process understandable to ordinary citizens, there are many moving parts in the system, and the technical language can be filled with jargon that is difficult for a layperson to understand.

The purpose of this brief article is to “unpack” the assessment process so that it can be more easily understood by homeowners.

Why Assessment Is Necessary

Assessment is a key part of the modern property tax system. In New York State, a “home rule” state, assessment is carried out by local assessors appointed by local elected officials. On Long Island, assessment is performed on a County basis; hence Nassau and Suffolk Counties maintain their own separate and distinct assessment systems.

The goal of the assessment process is simple:  to establish the market value of a given piece of property (including any structures upon it) so that the property owner shoulders an appropriate share of the overall tax burden.  Of course, those market values are imperfect, and homeowners can challenge those assessments every year, by filing tax grievances.

How Assessment Works

Today, Nassau County assessors do not personally inspect assessed properties in order to establish market values. Instead, they rely on CAMA (Computer Assisted Mass Assessment) software, which compares many variables associated with the property in question, including its location, condition, square footage, style and many other variables meant to serve as proxies for market value, such as recent sales of comparable properties.

In Nassau County, the system currently used by the Department of Assessment is called Prognose (if you’d like to know more about the way this software works, please read our article, Prognose, What We Know, What We Don’t Know, and What You Should Do, available on this blog).

Prognose is a sophisticated program, but its ability to provide accurate estimates of market value is dependent on the data fed into it. It behooves each and every homeowner to closely examine the data that Prognose lists on their properties.  A seemingly small error in the data can have a large impact on actual taxes.

A dedicated County website,, allows property owners to examine this data in detail; before going there, read our article, Make Sure that Nassau County’s Data on Your Property Agrees with Reality, available on this blog.

How Do Assessed Values Relate to the Taxes That You’ll Actually Pay?

One confusing aspect of the assessment system is determining how the assessed value correlates to the actual taxes paid.  The assessed value of the property is multiplied by the local tax rate to determine the homeowner’s tax liability.  So, if the assessed value decreases, the property taxes follow suit.  While the tax rates are set by the towns, school districts, villages and special districts in which a property is located, and cannot be challenged, the assessed value can be.

What You Can Do If Nassau County’s Assessment of Your Property is Wrong

The process by which property owners can contest the assessments published by the County is called “grieving.”  Need help with that?  You have until March 2, 2020 to authorize Maidenbaum to file your 2021/22 property tax grievance and take advantage of our advanced knowledge and many years of experience navigating the assessment process.

If you’re ready to get started, click here to authorize us to file a property tax grievance on your behalf.