What Is an IRS Notice of Deficiency, and How Long Do You Have to Respond?
An IRS notice of deficiency, often called the “90-day letter,” is a formal legal notice proposing additional tax you owe. Once you receive it, you have 90 days to file a petition with the U.S. Tax Court to challenge the amount before the IRS can legally assess and collect the tax. If you live outside the U.S., you get 150 days instead of 90.
Key facts about the notice of deficiency:
- 90-day deadline to petition Tax Court (150 days if your address is outside the U.S.)
- The deadline cannot be extended by the IRS or by requesting additional time
- Sent via certified mail to your last known address on file with the IRS
- Failing to respond means the IRS assesses the proposed tax automatically
The notice of deficiency typically arrives as Letter 3219 or Notice CP3219N. It details the tax year in question, the proposed changes to your return, and the additional tax the IRS believes you owe.
Your three options after receiving a notice of deficiency:
| Option | What happens |
| Agree with the proposed amount | Sign and return Form 5564 (waiver); the IRS assesses the tax |
| Disagree and petition the Tax Court | File a petition within 90/150 days; the case goes before a judge |
| Disagree, but do not petition | IRS assesses the tax; you pay, and then file a refund claim |
The 150-day window matters for expats. If you live abroad and your IRS address still shows a U.S. location, you may only get 90 days. Keep your address current with the IRS by filing Form 8822 so the correct deadline applies.
If the IRS has already sent collection notices before the deficiency letter, you may also have the right to request a Collection Due Process hearing. If your balance is the result of late filing, a tax professional can help you evaluate whether the proposed amount reflects credits and exclusions you may have missed.
Last updated on April 29, 2026
