Guide · Sources reviewed September 20, 2026

Nassau County tax grievance deadline

File with ARC from January 4 to March 1, 2027. The County’s FAQ says there’s no extension, so gather your record and evidence before the window closes.

Confirm the dates on Nassau County’s appeal instructions before filing. Every date in the cycle is on our deadlines page, with a calendar you can add.

Prepare a small review folder

Our suggested checklist keeps your research organized:

1. Save the record you reviewed, its year, and the date you retrieved it.
2. Write down property details you want to verify, such as living area or building type.
3. Keep notes on each sale you considered, including differences from your home.
4. Gather any existing representation agreement so you know what you have already authorized.

Start with your property check and use our assessment guide to work through the figures.

The 2028–29 cycle, date by date

An appeal filed in early 2027 is not about this year’s bills. It concerns the 2028–29 assessment, and the first bill calculated from it arrives in the fall of 2028. The County publishes the whole sequence on its Assessment Review Calendar:

The gap between filing and billing is the reason the deadline catches people out. By the time a higher bill arrives, the window to appeal the assessment behind it closed well over a year earlier.

Which assessment are you appealing?

The County issues an assessment each year, and its appeal deadline comes before the resulting tax bills. A pending appeal from a previous year does not replace a new-year application: the County advises appealing the most recent assessment if you disagree with it, even while you wait for a decision on last year’s. Check the assessment year in the official filing system. Our process guide sets the filing window in the context of the full review cycle, and our guide to the tentative roll covers what to check when it is published.

Don’t count on an extension

The County’s FAQ is direct on this point. Asked whether you can get an extension of time to file after March 1, 2027, it answers “No.” The County has sometimes extended the window for everyone (to March 18 in 2024 and March 31 in 2026), but announced it only weeks before the deadline, so plan on March 1. The FAQ also states that not receiving a notice of your tentative assessment does not extend your time to file, and that you can file even if no notice arrived. File early rather than on the last day, and keep the confirmation the County’s system sends you.

If you miss March 1

Once the filing period ends, the County states, you can no longer contest that assessment, and a prior year’s assessment cannot be appealed. Missing the window also closes the later steps for that year. The County says judicial review, including Small Claims Assessment Review, is available only if you applied to ARC and did not stipulate to a reduction. See the County’s SCAR page for its deadlines.

A missed year still leaves useful work:

• Check your record now. Wrong property details are worth finding before the next tentative roll, not during the filing window.
• Review exemptions separately. STAR and other exemptions run on their own applications and deadlines. See our exemptions guide.
• Plan for the next window. The County publishes a new tentative assessment on the first business day of each January, and the filing window follows. The reminder below will email you before it opens.

Filing yourself or using a representative

ARC accepts online applications without a filing fee; an attorney is not required. Avoid duplicate applications or authorizations. The County warns that many grievance services seek an authorization before the filing period opens, and that unresolved duplicate applications will be denied. If a representative or condominium board is filing for you, check that arrangement before filing independently. See the County’s instructions for details.

Keep separate assessments in view

A village assessment may have a different appeal process. Check with the local assessor rather than assuming the ARC deadline applies. The County FAQ explains the distinction, and New York State notes that villages that assess typically hear grievances on the third Tuesday of February, with dates that vary. Our village grievance guide covers that track, and our area pages summarize County assessments by school district, hamlet, and village.

Keep a record of your next step

Once you use the official filing system, save its confirmation and any documents you submitted. When ARC responds, our guide to ARC’s decision explains the options. A Good Grieves lookup or guide download does not file anything with the County.