# Notice of deficiency: what the IRS 90-day letter means

Source: https://backtaxesdesk.com/irs-notices/notice-of-deficiency
Publisher: Back Taxes Desk (backtaxesdesk.com), independent editorial site
Topic: IRS Notices and Letters
Last updated: 2026-09-18

> A notice of deficiency is the IRS's formal legal notice that it intends to assess more tax. You have 90 days from the notice date (150 if it is addressed to you outside the US) to petition the US Tax Court without paying first. The deadline cannot be extended. If you do nothing, the IRS assesses the tax and bills you.

## Key facts

- Common letter numbers: Letter 3219 (mail audits), Letter 531 (in-person audits), CP3219A, CP3219N
- Tax Court deadline: 90 days from the notice date, 150 if addressed outside the US
- Can it be extended: No, not by the IRS or the court
- Tax Court filing fee: $60, waiver available
- Small tax case limit: $50,000 or less per year in dispute
- To agree: Sign and return Form 5564

## What a notice of deficiency is

A notice of deficiency, often called a statutory notice of deficiency or the 90-day letter, is the legal step the IRS must take before it can assess additional income tax that you have not agreed to. The Taxpayer Advocate Service calls it your ticket to the Tax Court, because it is what lets you ask a judge to review the IRS figures before you pay anything.

It usually arrives at the end of a longer exchange: an audit, a [CP2000 underreporting proposal](https://backtaxesdesk.com/irs-notices/how-to-respond-to-cp2000) that was not resolved, or a substitute return the IRS prepared because a return was never filed.

| Letter or notice | Where it usually comes from |
| --- | --- |
| Letter 3219 | An audit conducted by mail |
| Letter 531 | An audit conducted in person |
| CP3219A | Third-party income that does not match your return, often after a CP2000 |
| CP3219N | A substitute for return when no return was filed |

Letters that are notices of deficiency

## The 90-day (or 150-day) deadline

The clock runs from the date on the notice, not the day it reached your mailbox. The notice itself shows the last day to file a petition. You have 90 days, or 150 days if the notice is addressed to a person outside the United States, and the Tax Court says it cannot extend that time.

If the last day falls on a Saturday, Sunday or a legal holiday in the District of Columbia, a petition filed the next business day is still on time. An electronic petition must reach the court by 11:59 p.m. Eastern Time on the last day.

### Worked date example

A notice of deficiency dated Monday, October 5, 2026 reaches day 90 on Sunday, January 3, 2027. Because that is a weekend, the last day to petition becomes Monday, January 4, 2027. Always check this against the date printed on your notice, since that is the one the court relies on.

> **Talking to the IRS does not stop the clock:** The IRS says the 90-day period cannot be extended, and filing a late return or sending more documents does not extend the time to petition. If you might want a judge to decide, file the petition on time and keep talking to the IRS in parallel.

## Options on a notice of deficiency IRS letter

### Agree and sign Form 5564

If the numbers are right, sign Form 5564, Notice of Deficiency-Waiver, and return it as the letter directs. You can pay some or all of the tax now or wait for the bill. Interest keeps accruing on the unpaid balance until it is paid in full, so paying now limits it.

### Disagree and petition the Tax Court

The petition goes to the United States Tax Court, not the IRS. You can file online through the court's DAWSON system or mail it, and the fee is $60, which the court can waive if you cannot pay. Attach a complete copy of the notice and do not attach receipts or returns at this stage. Our [Tax Court petition guide](https://backtaxesdesk.com/irs-audits/tax-court-petition) walks through the form.

If $50,000 or less per year is in dispute, you can choose the small tax case procedure. It is less formal, but the decision cannot be appealed. Our page on [how IRS appeals work](https://backtaxesdesk.com/irs-audits/irs-appeals-process) explains where the Independent Office of Appeals fits into disputes over audit results.

### Send the IRS more information

You can still write to the IRS with a signed explanation and documents, and it will work with you during the 90 days. This can resolve simple errors. It is a parallel track, not a substitute for a petition if the deadline is close.

### Pay, then claim a refund

The Tax Court is the only court where you can challenge the tax without paying first. If you pay the assessed amount, you can file a refund claim with the IRS and, if it is denied, sue in a US district court or the US Court of Federal Claims.

## What happens if you miss the 90 day letter IRS deadline?

If the IRS receives no signed waiver and no petition is filed, it assesses the proposed tax and penalties and sends a bill with interest. From that point, the account follows the normal collection path, and the 10-year collection period starts from the assessment date.

1. Expect a first balance-due notice, then reminders if it stays unpaid.
2. If you have new information, ask for [audit reconsideration](https://backtaxesdesk.com/irs-audits/irs-audit-reconsideration). This generally works only while the assessed tax is unpaid.
3. If you already paid, file a refund claim instead, and go to district court or the Court of Federal Claims if it is denied.
4. If you cannot pay, look at payment plans or hardship status before enforcement letters arrive.

If the deficiency came from a substitute return, filing your own correct return is often the best fix; our page on the [IRS substitute for return](https://backtaxesdesk.com/unfiled-returns/irs-substitute-for-return) explains that route.

## Getting help before the deadline

A Tax Court petition is a legal filing, so it is worth getting advice early if the amount is large. Attorneys, CPAs and enrolled agents can represent you before the IRS, and Low Income Taxpayer Clinics help eligible taxpayers in IRS disputes for free or a small fee. Our page on [Low Income Taxpayer Clinics](https://backtaxesdesk.com/tax-help/low-income-taxpayer-clinic) covers who qualifies.

For other letters in the same family, see the [IRS notices guide](https://backtaxesdesk.com/irs-notices).

## Common questions

### What is a notice of deficiency from the IRS?

It is the formal letter the IRS must send before assessing extra income tax you have not agreed to. It gives you 90 days, or 150 if addressed outside the US, to petition the US Tax Court.

### Can the 90-day deadline on a notice of deficiency be extended?

No. The Tax Court cannot extend it, and sending the IRS more information or filing a late return does not pause it. Only a weekend or District of Columbia holiday on the last day moves it to the next business day.

### What happens if I miss the Tax Court deadline?

The IRS assesses the proposed tax and bills you. You can still ask for audit reconsideration with new information, or pay and file a refund claim, but you cannot go to Tax Court without paying first.

### What if I agree with the deficiency?

Sign and return Form 5564, Notice of Deficiency-Waiver, and either pay now or wait for the bill. Interest and any penalties are added to the final amount.

### Is Letter 3219 the same as CP3219A?

Both are statutory notices of deficiency with the same 90-day Tax Court deadline. Letter 3219 usually follows a mail audit, while CP3219A usually follows an income mismatch such as an unresolved CP2000.

### How much does it cost to petition the Tax Court?

The filing fee is $60. The court can waive it if you file an application showing you cannot pay.

## Sources

- [Letter 3219, Notice of Deficiency (Taxpayer Advocate Service)](https://www.taxpayeradvocate.irs.gov/notices/letter-3219/)
- [Understanding your CP3219A notice](https://www.irs.gov/individuals/understanding-your-cp3219a-notice)
- [Understanding your CP3219N notice](https://www.irs.gov/individuals/understanding-your-cp3219n-notice)
- [US Tax Court: Starting a case](https://www.ustaxcourt.gov/petitioners_start.html)
- [US Tax Court: Case procedure](https://www.ustaxcourt.gov/case-procedure/)
- [Publication 556, Examination of Returns, Appeal Rights, and Claims for Refund](https://www.irs.gov/publications/p556)