A tax assessment notice is a letter from the IRS or a local tax authority stating that you owe more than you reported, and your response — or silence — before the deadline printed on the notice decides what happens next. Federal notices typically give you 30 or 90 days. Local property tax notices can give even less. If you let the deadline pass, the amount the agency proposes becomes your legal liability, and collection tools like liens, levies, and wage garnishments open up. Everything below is organized around meeting that deadline.
First, Check the Deadline and Confirm the Notice Is Real
Open the envelope the day it arrives and look at the top of the first page. You are looking for two things: the notice date and the response deadline. Write the deadline on your calendar before you do anything else. For a Notice of Deficiency, the deadline is exactly 90 days from the mailing date (150 days if you are outside the United States), and the Tax Court will not accept a late petition for any reason.1Internal Revenue Service. Understanding Your CP3219A Notice
Then confirm the notice is legitimate. A real IRS notice arrives by mail, carries a notice number in the upper right corner, and references a specific tax year and amount. It will never demand payment by gift card or threaten arrest. You can verify any federal letter by logging into your IRS Online Account to see whether it appears in your file, or by calling the IRS using the number listed on irs.gov rather than any number printed on the letter itself. If a private collection agency contacts you about a federal tax debt, the IRS will have already mailed you a separate CP40 notice containing a Taxpayer Authentication Number the agency must reference.
Identify Which Notice You Received
Your rights and response options depend entirely on the type of notice, so match yours to one of the categories below before deciding what to do.
CP2000 (Proposed Changes)
A CP2000 is not a bill and not an audit. The IRS compared the income reported on your return to data filed by employers, banks, and brokerages and found a mismatch. The notice proposes changes and asks you to agree or disagree by a specific date. If you ignore it, the IRS will eventually convert the proposal into a bill.
Notice of Deficiency (CP3219A or CP3219N)
This is the 90-day letter. It is the IRS formally determining that you owe additional tax and starting a rigid 90-day clock to petition the U.S. Tax Court. The IRS has no power to extend this deadline. Miss it and the assessment becomes final.
Substitute for Return
If you did not file a return at all, the IRS can prepare one for you using third-party income reports. These substitute returns use the least favorable assumptions available: single filing status, no dependents, and nothing beyond the standard deduction. The resulting bill is almost always inflated, and the only way to replace it is to file a properly completed original return for that year.
30-Day Letter
After an audit, if the examining agent proposes changes you disagree with, the IRS issues a 30-day letter inviting you to request a conference with the IRS Independent Office of Appeals before the case escalates to a Notice of Deficiency.2Taxpayer Advocate Service. Letter 525 Audit Report/Letter Giving Taxpayer 30 Days to Respond
Property Valuation Notice
These come from your county or municipal assessor and set the fair market value used to calculate your property tax bill. Reassessment cycles vary widely by state. A majority of states require reassessment at least every three years, while some allow up to ten. If the assessed value exceeds what the property would actually sell for, you can appeal to a local Board of Equalization or similar body. The appeal window is usually much shorter than federal windows.
Federal and property tax rules do not overlap. The deadlines, forums, and standards for each are entirely separate, so do not assume the process you read about for one applies to the other.
Decide Whether the Notice Is Right
Gather everything related to the tax year in question: your filed return, every W-2 and 1099, receipts for deductions you claimed, and any prior correspondence with the IRS. If you used tax software, pull the saved return and calculation worksheets.
Then do a line-by-line comparison between the figures in the notice and the figures on your return. You are sorting the situation into one of two buckets. Either the IRS is correct — you missed a 1099, miscalculated something, or claimed a deduction you cannot substantiate — or the IRS is wrong, because it attributed income to you that belongs to someone else or disallowed something you can prove. That answer dictates your next step. A correct notice points you toward payment arrangements and penalty relief. A wrong notice points you toward Appeals or Tax Court.
If the Notice Is Correct: Pay or Reduce What You Owe
Pay in Full
If you have the funds and the notice is accurate, paying the full tax, penalty, and interest by the deadline is the fastest way to stop additional charges from accruing. Reference the tax year and notice number on your payment. For small assessments, this is also the sensible choice when fighting the notice would cost more in time and professional fees than the amount at stake.
Ask for Penalty Abatement
If you owe the tax but believe the penalties are unfair, two routes exist for getting them reduced or removed. First-Time Penalty Abatement is granted administratively if you filed the same type of return for the prior three tax years, had no penalties during that period (or any prior penalty was removed for an acceptable reason), and are current on all filing and payment obligations.3Internal Revenue Service. Administrative Penalty Relief You can request it by calling the number on your notice.
Reasonable cause abatement applies when circumstances beyond your control prevented timely filing or payment. Serious illness, a natural disaster, the death of an immediate family member, inability to obtain necessary records, and reliance on incorrect advice from a tax professional can all qualify. You submit Form 843 or a written explanation with documentation, and the IRS evaluates whether you exercised ordinary care and still could not comply. Abatement removes penalties only; the underlying tax and interest remain. But stripping a 25% failure-to-file penalty off a $15,000 balance saves $3,750, so it is almost always worth asking.
Set Up an Installment Agreement
If you cannot pay in a single lump sum, the IRS offers formal payment plans. A short-term plan gives you up to 180 days to pay in full with no setup fee. A long-term installment agreement spreads payments monthly. Setup fees for long-term plans as of March 2026 range from $22 for an online direct debit agreement to $178 if you apply by phone or mail without direct debit, with a fee waiver available for low-income taxpayers.4Internal Revenue Service. Payment Plans; Installment Agreements One detail worth knowing: once you are on an approved installment agreement and your filings are current, the failure-to-pay penalty drops from 0.5% to 0.25% per month.5Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax
Offer in Compromise
An Offer in Compromise settles your tax debt for less than the full amount. The IRS accepts an OIC on one of three bases: doubt as to liability, doubt as to collectibility, or effective tax administration (where collection would create economic hardship or be fundamentally unfair).6Internal Revenue Service. Topic No. 204 Offers in Compromise Acceptance rates are low and the process demands detailed financial disclosure, but for taxpayers who genuinely cannot pay, it is a legitimate path.
Currently Not Collectible Status
If your income barely covers basic living expenses, the IRS can place your account in Currently Not Collectible status. This temporarily halts levies and garnishments. The debt itself does not disappear: penalties and interest keep accruing, and the IRS may file a federal tax lien to protect its interest. If your finances improve on a later review, collection resumes.7Internal Revenue Service. Temporarily Delay the Collection Process You request CNC by submitting a Collection Information Statement (Form 433-F or 433-A) with proof of income, expenses, and assets.
If the Notice Is Wrong: How to Dispute It
Respond to a 30-Day Letter
You have 30 days to submit a formal written protest requesting an Appeals conference, or a simplified Small Case Request on Form 12203 if the total proposed additional tax and penalties for each period is $25,000 or less.8Internal Revenue Service. Preparing a Request for Appeals The Appeals conference is an informal settlement discussion, not a courtroom. The Appeals Officer weighs the strength of each side’s position and has authority to settle based on how likely the IRS is to prevail in court. That often produces a compromise unavailable at the examination level.
Petition the U.S. Tax Court
If you received a Notice of Deficiency, you have 90 days from the mailing date (150 if abroad) to file a petition with the U.S. Tax Court.9GovInfo. 26 USC 6212-6213 – Notice of Deficiency and Time for Filing Petition The filing fee is $60.10United States Tax Court. Guidance for Petitioners: Starting a Case This is the only forum where you can dispute the deficiency without paying the tax first.
Miss the 90 days and the assessment becomes final. Your only remaining option is to pay in full and then file a refund claim; if the IRS denies the refund, you can sue in U.S. District Court or the Court of Federal Claims within two years. That pay-first path is far costlier than a timely Tax Court petition, which is why the 90-day date is the single most important one on any Notice of Deficiency.
Appeal a Property Tax Assessment
Property disputes go to your local Board of Equalization or similar review body, using a jurisdiction-specific form and a small filing fee. The hearing is quasi-judicial: you present evidence that the assessed value exceeds fair market value, and the board rules.
The strongest evidence is recent sales of comparable properties. Aim for three to five sales that closed within the past year involving homes of similar size, age, and condition. If your property has a significant defect the assessor’s mass appraisal method missed, a professional appraisal strengthens the case. Residential appraisals for tax appeals typically cost several hundred dollars, but multi-year tax savings can easily justify the expense. Deadlines vary by jurisdiction and are generally short, so check your local assessor’s website the day the notice arrives.
What Penalties and Interest Add While You Wait
Penalties and interest are what turn a manageable bill into an overwhelming one, and they start running the moment you miss a deadline.
The failure-to-file penalty is 5% of unpaid tax per month or partial month, capped at 25%.11Internal Revenue Service. Failure to File Penalty A fraudulent failure to file triples the rate to 15% per month with a 75% cap.5Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax The failure-to-pay penalty is 0.5% per month, also capped at 25%; when both penalties apply in the same month, the file penalty is reduced so the combined rate is 5% rather than 5.5%.12Internal Revenue Service. Failure to Pay Penalty Once the IRS sends a notice of intent to levy and ten days pass without payment, the failure-to-pay penalty doubles to 1% per month.
Interest runs on top of all of that from the original due date, set quarterly at the federal short-term rate plus three points. The first quarter of 2026 is 7%, dropping to 6% for the second quarter.13Internal Revenue Service. Internal Revenue Bulletin 2026-8 It compounds daily and runs on penalties too, not just the tax. Unlike penalties, interest cannot be abated unless the IRS caused an unreasonable delay. A $10,000 balance ignored for two years can easily grow 40% to 50% once everything stacks.
What Happens If You Do Nothing
Ignoring a tax assessment notice is the worst possible move. If you fail to respond to a Notice of Deficiency within 90 days, the IRS assesses the full proposed amount and starts collection. Collection tools include a federal tax lien, a public claim against your property that damages credit and complicates sales and loans, and a levy, the actual seizure of bank funds and wages.14Internal Revenue Service. What’s the Difference Between a Levy and a Lien?
Ignoring a Substitute for Return turns that inflated assessment into your legal liability. You lose the deductions, credits, and better filing status a proper return would have given you. Filing an original return later is still possible, but reopening a finalized SFR assessment takes far more effort than responding on time.
When the IRS May Be Out of Time
The IRS generally has three years from the date you filed your return to assess additional tax for that year. If you never filed, there is no time limit, which is why filing even a late return starts the clock and eventually produces finality. A fraudulent return also has no statute of limitations.15Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection
If a notice reaches you for a tax year older than three years, check whether you actually filed for that year. If you did, and there is no fraud or substantial understatement alleged, the assessment may be time-barred. The tolling rules and exceptions are technical, so this is a question worth putting to a tax professional before you respond.
When to Bring in Help
Not every notice needs a professional. A CP2000 proposing a small adjustment for a 1099 you forgot is usually straightforward to handle yourself. But some situations are high-risk enough that going it alone is a serious mistake: audit-based assessments involving business deductions, any Notice of Deficiency with a Tax Court deadline, Substitute for Return assessments spanning multiple years, and any notice where the liability exceeds what you can realistically pay.
If you cannot afford representation and the IRS is causing financial hardship, the Taxpayer Advocate Service is a free, independent organization within the IRS that can intervene. TAS takes cases involving economic harm, an immediate threat of adverse action like a levy, or an IRS system failure that has gone unresolved more than 30 days past the normal timeframe.16Internal Revenue Service. IRM 13.1.7 Taxpayer Advocate Service (TAS) Case Criteria Low Income Taxpayer Clinics, which operate independently of the IRS, also provide free or low-cost representation to qualifying taxpayers in IRS disputes.
Whichever path you take, send every response by certified mail with return receipt requested. If a deadline dispute ever arises, that receipt is the only proof that counts.