Nassau County Property Tax Grievance: Deadline, Where to File and What Happens Next

A grievance is the formal route for contesting what the County assigns a property for tax purposes. It changes the assessment, and the assessment sets your share of the levy, so it sits next to Nassau County property taxes and the STAR exemption in any bill review. For sellers, it is also part of the selling guide, because an assessment is one of the figures a buyer sees.

What a grievance can and cannot change

Assessors can only address a property’s assessment, not the amount of the taxes. The taxes to be collected are set by local jurisdictions, not by the assessor. A grievance therefore targets the assessed value. It does not touch a school budget or a village rate.

Taxpayers have the right to file a grievance regarding their property’s assessed value. The Assessment Review Commission reviews the valuation set by the Department of Assessment and makes determinations on grievance applications filed on time. It is an independent agency, separate from the Department of Assessment.

If an informal discussion does not reduce the assessment and the owner still thinks it is too high, the owner may contest it. Bringing questions to the assessor before the tentative roll is filed is helpful. All property owners should check the tentative assessment roll each year to confirm their assessments are fair and that they receive the exemptions they expect.

A grievance can also claim an excessive assessment when a property was denied all or part of a partial exemption, such as senior citizens, veterans or STAR.

Nassau County grievance deadline and filing window

The 2026 window closed March 31, 2026. The County first gave January 2, 2026 to March 2, 2026 for appeals based on the tentative assessment, and the commission’s page carries a notice that the filing period was extended to March 31, 2026. The County’s FAQ lists March 2, 2026 as the deadline for an application for correction and answers no to a request for more time after that date. The two County pages differ on the date.

The Town of Oyster Bay gives the grievance period as January 2 to March 1. The County runs the commission, so the County’s dates control. A new tentative assessment is published on the first business day in January each year, and the next opportunity to file follows the next tentative roll.

A pending decision on last year’s application does not move the date: the County ties the filing deadline to the new assessment, with or without a determination on the prior application. Failing to receive an assessment notice does not extend the time to file. The Department of Assessment must value all property at the same time even when an appeal is pending.

How to file: AROW online or Form AR1

An appeal can be filed on the website through the online appeal system called AROW, Assessment Review on the Web. Filing online is recommended because it is faster and more accurate. An online appeal can be filed for any type of property. A filer must register to file an appeal, but the sale locator and public inquiry functions work without registering. The sale locator is optional.

Paper filing is still available. During the grievance period, taxpayers may examine the assessment rolls and obtain grievance applications, Form AR1, at the Nassau County Assessment Review Commission. The commission’s Mineola office is at 240 Old Country Road, 5th Floor, Mineola, NY 11501. Questions go to (516) 571-3214 or ARC@nassaucountyny.gov.

The commission uses three application forms:

• AR1 contests the value of an exclusively residential one-, two- or three-family house or a Class 1 condominium unit.
• AR2 contests the value of all other property types.
• AR3 is for a disagreement over the property’s tax class or exemptions.

Attachments are welcome: online filers can attach word documents, spreadsheets, digital photographs and scanned images, and video files are not accepted. Online filers get an email notification that the application was received. Adjacent tax lots used as a single property go on one appeal that lists all the parcel numbers. Duplicate applications are denied, so do not sign multiple authorizations.

Only the owner or another applicant-taxpayer, or a representative with the applicant’s written authorization, may act on an application. Using a representative is not required, and when one is hired, the commission may speak only to the representative.

Who can file, and what the commission can do

The owner, or one of several owners, can file. A lessee of an entire property who pays all the taxes also qualifies. A person with a written contract to buy may file as contract vendee but loses standing if the sale does not close. A qualified fiduciary, such as an executor or a person named in a notarized power of attorney, can authorize an appeal when the owner has died or cannot sign. A representative’s authorization is valid for only one filing.

The commission either reduces an assessment or leaves it unchanged, and cannot increase it. It will consider the claimed value and the evidence supplied, without requiring proof of why the Department of Assessment’s estimate was wrong. Professional appraisers and other qualified professionals review applications, and the owner need not appear in person. For commercial property, appraisers consider rental income potential, sales of similar properties or cost to build.

Some things are outside its reach. The commission cannot hear an appeal of the tax bill, because each tax district’s budget process sets the rates. A prior year’s assessment cannot be appealed once its filing period expires. Each year’s assessment is a separate determination, so an owner who filed last year files again only if the owner disagrees with the new assessment. In a cooperative the corporation’s board may appeal the single assessment, and individual shareholders cannot.

Many North Shore properties sit in places with their own assessors. Property assessed by the City of Glen Cove, the City of Long Beach or a village is appealed to the local Board of Assessment Review, and a filing with the commission does not preserve review of the city or village assessment. The filing dates and procedures are different.

Class 1 owners get one more signal. The County advises appealing when a Class 1 assessed value rises more than 6%, unless the increase reflects new construction or renovation, and the 6% limit applies to total assessed value rather than the appraised fair market value. Even when the adjusted market value looks right, an owner may appeal the tax class, exemption determinations or calculation of assessment limitations or transition assessments.

What a grievance has to contain

The State’s grievance form guide sends Nassau County residents to the Nassau County Assessment Review Commission. A grievance must cover the total assessed value of the whole parcel, which includes the land. It cannot be based only on the assessed value of the land. The land assessment and total assessment appear on the assessment roll.

The form asks for the property’s market value based on the sources of information suggested in RP-524, Part II. For most residential owners, comparable sales priced below the assessor’s estimated market value are the best support for the case. Condominium boards may appeal assessments on behalf of unit owners. A condo owner may appeal a unit individually but should contact property management first to avoid duplicate applications.

What happens after you file

The commission takes a full year to review all appeals, and the FAQ puts the range at up to 15 months. Final determinations are issued by March 31 of the year after the appeal is filed. The final determination appears on the final roll, published on the first business day of April, and notices are mailed at the same time. An appeal of an assessment published in January 2026 shows up on the April 2027 final roll.

A reduction offer need not be accepted. Small claims and other judicial proceedings can be filed starting the first business day in April.

If the owner disagrees with the final determination, an appeal can be filed in New York State Supreme Court. A taxpayer may file a Small Claims proceeding or a judicial proceeding if qualified. Dollar savings depend on the district rates applied to the corrected value, which the property tax guide walks through.