Introduction
On Long Island, challenging your property tax bill is the norm, not the exception. 62% of Long Island homeowners have filed a property tax grievance at least once, nearly triple the national rate of 22%.
Here is what many homeowners miss: a Nassau grievance is filed for a single tax year, so the authorization that lets an agent file for you does not roll over. Each new tax year is a fresh decision about who represents you.
This guide covers whether you must reauthorize, which form does it, how to switch or cancel a representative, and how to avoid a duplicate-authorization denial. At Ownwell, we file Nassau grievances directly, so we can walk you through the mechanics from experience.
Key Takeaways
A Nassau grievance covers one tax year, so you must authorize a representative each year; last year's authorization does not carry into the new roll.
Representatives are authorized on Nassau's AR-10, filed through Assessment Review on the Web (AROW); statewide, part four of Form RP-524 does the same.
You can switch representatives or file for yourself; you are not locked to last year's firm.
Never sign more than one authorization per year; unresolved duplicates are denied by the Assessment Review Commission (ARC).
Submit before the filing deadline, which falls in January through March; always confirm the current year's date.
Do You Have to Reauthorize a Property Tax Agent in Nassau County Every Year?
Yes. In practice, you reauthorize a representative every year, because each grievance challenges only the current tentative assessment roll. You cannot grieve prior years, so the right to file resets annually, and so does the authorization behind it.
Nassau routes residential grievances through ARC rather than a local Board of Assessment Review, as most other New York counties do. The tentative roll is where your assessed value for the coming tax year first appears. If that number looks too high, the grievance window lets you push back, and only an authorized representative can do it on your behalf.
Here is the annual chain in plain terms: the county publishes a new tentative roll, you or your representative file a grievance against that year's assessed value, and that filing needs a current-year authorization to be valid.
Many legacy Long Island firms auto-contact returning clients each January to renew. That outreach is convenient, but the legal filing still requires a fresh authorization tied to the new tax year. A reminder email is not the same as a signed, current authorization.
Filing every year is normal here. In fact, 93% of Long Island homeowners agree the property tax system penalizes those who don't file a grievance. Treat each annual reauthorization as a checkpoint to confirm your representation is still the best deal.
We won't re-explain the full filing walkthrough here; our complete Nassau County grievance filing guide covers building and submitting the case start to finish. Because the clock resets, a firm that filed for you last year has no standing this year until you sign again. That is good news: every January is a clean slate to compare options, including moving to Ownwell.
How Much Are You Over Paying?
How to Authorize a Representative in Nassau County: AR-10 and RP-524
In Nassau County, you authorize a representative on the AR-10, the "Authorization to Represent an Individual Taxpayer in an Application for Correction of Property Tax Assessment." It ties one representative to one property for one specific tax year.
The AR-10 captures the details ARC needs to verify who is filing on your behalf:
The tax year the authorization applies to
The representative's name and representative number
The aggrieved party and relationship to the property (owner, tenant, or contract vendee)
The parcel ID and property address
Your signature and the date
Submit the form online through AROW, Nassau's electronic filing system. A representative filing on 10 or more properties they do not own must register with ARC, and all attorneys must register regardless of volume.
The AR-10 is Nassau-specific. Outside New York City and Nassau, authorization is handled in part four of Form RP-524, the statewide grievance form issued by the New York State Department of Taxation and Finance.
Accuracy matters here. A missing parcel ID or an authorization dated to the wrong tax year can stall or invalidate the filing, so we double-check every field before it goes to ARC.
When you sign up with Ownwell, we prepare and submit the authorization and grievance for you, so you aren't decoding form fields on a deadline. One authorization equals one representative for one year, and that single signed AR-10 is all we need to start working your case.
How to Change or Cancel Your Nassau County Property Tax Representative
For each new assessment, you can change representatives or file for yourself. Signing with a firm one year does not bind you to that firm the next. When the roll resets, so does your choice.
Switching cleanly comes down to three steps:
Decide before you sign anything for the new tax year.
Sign a single authorization with the representative you actually want.
Make sure no prior-year firm's authorization is still active for the same new roll.
The safest time to switch is early in the grievance window, before any firm files on your behalf. Once you submit a grievance under an old authorization, untangling it is harder than starting clean.
Before you assume you are committed, check what you signed. Some legacy Long Island firms use flat fees or multi-year contract language, so read the terms rather than renewing on autopilot.
Hesitation is common. Among Long Island homeowners who have never filed, 16% said the process was too confusing, and 6% cited distrust of grievance firms, preferring to handle it themselves or skip filing. Switching to a transparent, contingency-based representative removes both of those barriers.
If you are leaving another provider, Ownwell can help. Our Cancel Non-Ownwell Service handles the handoff so you don't have to manage two firms at once.
What Happens If You Sign Duplicate Authorizations?
Don't do it. If two representatives hold active authorizations for the same property and tax year and the conflict isn't resolved, ARC denies the application outright. A denied grievance means no reduction that year.
Duplicate authorizations usually happen by accident, not by intent, for example when a homeowner responds to a renewal notice from last year's firm and also signs up with a new one.
The practical rule is simple: only one authorization can stand per property, per year. If you decide to represent yourself after signing with a firm, or you move from one firm to another, you must confirm the earlier authorization is withdrawn before the deadline.
Reauthorize, Switch, or File Yourself: How to Decide
Your realistic options each year are to file yourself, use a traditional Long Island firm, or authorize Ownwell. They differ most on cost, lock-in, and how much of the work lands on you.
One term to know first: if ARC denies your grievance or under-offers, the next level is Small Claims Assessment Review (SCAR), a low-cost, court-supervised review available to residential homeowners.
Factor | File Yourself (DIY) | Legacy Long Island Firm | Ownwell |
|---|---|---|---|
Fee | No fee, but your time | Often a flat fee or a share of savings; terms vary | 25% of what we save you, with no upfront cost |
Contract lock-in | None | Sometimes multi-year or auto-renewing | None; you decide each year |
Effort | You do all research and filing | Low, once signed | Low; we handle it end to end |
AROW filing | You file | Firm files | We file |
SCAR escalation | You file and attend | Varies by firm | We escalate when warranted |
Here is what a reduction looks like on a typical Long Island home. Take a $650,000 home at a 0.71% effective tax rate, with a 15% assessed-value reduction.
Figure | Before | After |
|---|---|---|
Assessed value | $650,000 | $552,500 |
Effective tax rate | 0.71% | 0.71% |
Annual tax bill | $4,615 | $3,923 |
Annual savings | $692 |
That $692 is not a one-time win. A successful reduction becomes your new assessed-value baseline, so the lower number carries into future rolls and compounds year over year. That is exactly why who you reauthorize each year matters.
If your assessment barely moved and you enjoy the paperwork, DIY can work. If you want representation without a lock-in or an upfront bill, our contingency model aligns our incentives with your savings: we only get paid when you do.
Want to Try What Made Ownwell Famous?
How Ownwell Can Help With Your Nassau County Grievance
When you work with Ownwell, we handle the full grievance from start to finish. We prepare the AR-10 authorization, build your evidence with a comparative market analysis, file with ARC through AROW, and escalate to SCAR when the numbers justify it.
Our Nassau County results speak for themselves: we win 93% of the time and save homeowners an average of $1,462. We work on a 25% contingency with no upfront cost, so you only pay if we lower your bill. Across markets, we hold a 4.7 rating from 3,000+ reviews.
There is no multi-year contract and no risk to trying us. If we don't save you money, you owe us nothing.
Frequently Asked Questions
Do I Have to Reauthorize My Property Tax Agent in Nassau County Every Year?
Yes. Each grievance covers only the current assessment roll, so you need a new authorization for every tax year.
What Form Authorizes a Representative to File My Nassau Grievance?
Nassau uses the AR-10 "Authorization to Represent," submitted through AROW. Part four of Form RP-524 is the statewide equivalent.
Can I Switch Property Tax Representatives or File for Myself This Year?
Yes. You can change representatives or self-file for the new assessment, as long as only one authorization is on file for that year.
When Is the Nassau Authorization and Grievance Deadline?
It falls in the January-through-March window and has been extended by about a month each year. The 2027/28 deadline was extended to March 31, 2026, so confirm the current year's date with ARC.
