A tax assessment notice is a letter from the IRS or a local tax authority stating that you owe more than you reported, and the most important thing on it is the response deadline printed near the top. Federal notices generally give you 30 or 90 days; property valuation notices sometimes give as little as 30 calendar days. Miss that window and the assessed amount becomes final, which opens the door to liens, wage garnishments, and bank levies. Everything else in this guide flows from that deadline.
Confirm the Notice Is Real Before You Act
Tax scams imitate official mail well enough that verifying the sender is a real first step, not paranoia. A genuine 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.
Log into your IRS Online Account and check whether the letter appears in your file. You can also call IRS customer service using the number listed on irs.gov, not the number printed on the letter itself. If a private collection agency contacts you, the IRS will already have sent you a separate CP40 notice containing a Taxpayer Authentication Number the agency must reference.
Find the Deadline and Identify the Notice
Once you know the letter is genuine, find the notice date and the response deadline and write them on your calendar the same day. Which type of notice you received determines what that deadline means and what rights you still have.
CP2000: Proposed Change, Not a Bill
The CP2000 is the most common federal notice. It is not an audit and not a final bill. The IRS compared your return against income data reported by employers, banks, and brokerages, found a mismatch, and is proposing changes. You can agree or disagree by the date shown. If you do nothing, the IRS eventually converts the proposal into a bill.
Notice of Deficiency: The 90-Day Letter
The Notice of Deficiency (CP3219A or CP3219N) is the most consequential federal notice you can receive. It gives you exactly 90 days from the mailing date, or 150 days if you are outside the United States, to petition the U.S. Tax Court.1Internal Revenue Service. Understanding Your CP3219A Notice The Tax Court cannot hear a late petition for any reason, and the IRS cannot extend the deadline. This is the one date on any tax notice you cannot afford to miss.2GovInfo. 26 USC 6212-6213 – Notice of Deficiency and Time for Filing Petition
Substitute for Return
If you did not file at all, the IRS can prepare a return for you using third-party income data. The resulting bill is almost always inflated because the IRS uses the least favorable assumptions: single filing status, no dependents, and only the standard deduction. The only way to replace a Substitute for Return with something realistic is to file a properly completed original return for that year.
30-Day Letter After an Audit
If your return was audited and you disagree with the examiner’s proposed adjustments, the IRS sends a 30-day letter offering you a conference with the Independent Office of Appeals.3Taxpayer Advocate Service. Letter 525 Audit Report/Letter Giving Taxpayer 30 Days to Respond Ignore that window and the case escalates to a Notice of Deficiency with its harder 90-day clock.
Property Valuation Notices
Property notices come from your county or municipal assessor and set the fair market value assigned to your real estate, which is then multiplied by the local rate to produce your tax bill. Appeals go to a local Board of Equalization or similar body, not the IRS, and appeal windows vary by jurisdiction but are generally shorter than federal deadlines. Do not assume federal rules apply here. Check your assessor’s website the day the notice arrives.
Check Whether the Notice Is Actually Right
Before you decide how to respond, you need to know whether the IRS is correct. Pull the return for the year in question, along with every W-2, 1099, K-1, receipt, and prior letter connected to that year. If you used tax software, open the saved return and the calculation worksheets.
Compare the figures in the notice against the figures on your return, line by line. You are trying to place the notice in one of two categories. Either the IRS is right (a missing 1099, an arithmetic error, a credit that did not actually apply), or the IRS is wrong (income attributed to you that belongs to someone else, a legitimate deduction disallowed, a return the IRS did not process). That single distinction determines your path. If the notice is correct, your work is around payment and penalty relief. If it is wrong, your work is a formal dispute.
If the Notice Is Correct: Pay or Arrange to Pay
Pay in Full
If you have the funds and the assessment is right, paying the tax, penalty, and interest by the deadline stops further penalties and interest from accruing. Reference the tax year and notice number on the payment. For small assessments, this is almost always cheaper than fighting.
Ask for Penalty Abatement
The tax and interest are usually not negotiable, but penalties often are. Two routes exist. First-Time Penalty Abatement is granted administratively if you filed the same type of return for the prior three years, had no penalties during that period (or any prior penalty was removed for an acceptable reason), and are current on all filings and payments.4Internal Revenue Service. Administrative Penalty Relief Call the number on the notice to request it.
Reasonable cause abatement covers situations beyond your control: serious illness, natural disaster, death in the immediate family, inability to obtain records, or reliance on incorrect professional advice. Submit Form 843 or a written explanation with documentation. The IRS evaluates whether you exercised ordinary care and still could not comply. Removing a 25% failure-to-file penalty from a large balance can save thousands, so this request is worth making even when the underlying tax is not in dispute.
Set Up an Installment Agreement
If you cannot pay at once, the IRS offers formal payment plans. A short-term plan gives you up to 180 days with no setup fee. A long-term installment agreement spreads payments over months, with setup fees ranging from $22 for an online direct debit agreement to $178 for a phone or mail application without direct debit as of March 2026. Low-income taxpayers may qualify for a fee waiver.5Internal Revenue Service. Payment Plans; Installment Agreements
A detail worth knowing: once you are on an approved installment agreement and filed on time, the failure-to-pay penalty drops from 0.5% to 0.25% per month.6Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax Interest keeps accruing, but the plan is meaningfully cheaper than doing nothing.
Offer in Compromise
An Offer in Compromise settles the debt for less than the full amount. The IRS considers three grounds: doubt as to liability (a real argument you don’t owe it), doubt as to collectibility (your assets and income are less than the debt), or effective tax administration (paying in full would create economic hardship or be fundamentally unfair).7Internal Revenue Service. Topic No. 204 Offers in Compromise Acceptance rates are low and the financial disclosure is extensive. It remains a legitimate option for taxpayers who genuinely cannot pay.
Currently Not Collectible Status
If your income barely covers basic living expenses, the IRS can place your account in Currently Not Collectible status, which temporarily halts levies and garnishments. The debt does not go away. Penalties and interest continue, and the IRS may file a lien to protect its position. Expect periodic financial reviews, and expect collection to resume if your situation improves.8Internal Revenue Service. Temporarily Delay the Collection Process You will need to submit a Collection Information Statement (Form 433-F or 433-A) with proof of income, expenses, and assets.
If the Notice Is Wrong: Dispute It
Request an Appeals Conference
If you disagree with the findings in a 30-day letter after an audit, submit a formal written protest within the 30 days, or a Small Case Request on Form 12203 if the total proposed additional tax and penalties for each period is $25,000 or less.9Internal Revenue Service. Preparing a Request for Appeals The conference is an informal settlement discussion. An Appeals Officer weighs how likely the IRS would be to win in court and has authority to compromise on that basis, which often produces a better outcome than the examination itself.
File a Tax Court Petition
If you received a Notice of Deficiency, the petition to the U.S. Tax Court must be filed within 90 days of the mailing date (150 if you are abroad). The filing fee is $60.10United States Tax Court. Guidance for Petitioners: Starting a Case The Tax Court is the only forum where you can dispute the deficiency before paying it.
Miss the 90 days and the assessment becomes final. Your only remaining route is to pay in full, file a claim for refund, and if the IRS denies it, sue in a U.S. District Court or the Court of Federal Claims within two years of the denial. That path is slower, more expensive, and requires you to fund the disputed tax first. File the Tax Court petition on time.
Appeal a Property Valuation
Property tax appeals go to your local Board of Equalization or a similar body, typically using a jurisdiction-specific form with a small filing fee. The hearing is quasi-judicial, and 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 did not catch, a professional appraisal strengthens the case. Residential tax-appeal appraisals typically run several hundred dollars, and multi-year tax savings often justify the cost.
What Happens If You Ignore It
Doing nothing is the worst response, and it happens more than you would expect because people set anxious mail aside. If you do not petition the Tax Court within 90 days of a Notice of Deficiency, the IRS assesses the proposed amount and starts collecting. That means a federal tax lien, which is a public claim against your property that damages your credit and complicates loans and real estate sales, and eventually a levy, which is the actual seizure of bank funds or wages.11Internal Revenue Service. What’s the Difference Between a Levy and a Lien?
If you ignore a Substitute for Return notice, that inflated assessment becomes your legal tax liability. You lose the deductions, credits, and filing status you could have claimed on an original return. You can still file for that year afterward, but reversing a finalized SFR takes far more time and effort than responding to the notice would have.
Send Every Response by Certified Mail
Whatever route you take, mail every response certified with return receipt requested. If a deadline is ever contested, that receipt is the only proof that matters. Keep copies of everything you send.
When to Bring in a Professional
You do not need help with every notice. A CP2000 proposing a small adjustment based on a 1099 you forgot is usually manageable on your own. Bring in a tax professional when the notice involves audit-based adjustments to business deductions, any Notice of Deficiency with a Tax Court deadline, a Substitute for Return covering multiple years, or a total liability you cannot realistically pay.
If professional fees are out of reach and the IRS is causing you financial hardship, the Taxpayer Advocate Service is a free, independent organization inside the IRS that can intervene. TAS takes cases where you face economic harm, an immediate threat like a levy, or an unresolved issue that has run more than 30 days past normal timeframes.12Internal Revenue Service. IRM 13.1.7 Taxpayer Advocate Service (TAS) Case Criteria Low Income Taxpayer Clinics operate separately from the IRS and provide free or low-cost representation to qualifying taxpayers in disputes.
One last check before you do anything else: look at the tax year on the notice. The IRS generally has three years from the date you filed to assess additional tax, and if you filed on time and there is no allegation of fraud or substantial understatement, an older assessment may be time-barred.13Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection If you never filed for that year, no such time limit exists. The rules around tolling and exceptions get technical fast, so this is one place worth a professional’s second look before you write your response.