IRS Notice of Deficiency Letter Explained
A Notice of Deficiency, sometimes called a 90-day letter, is one of the most important documents the IRS can send you. It is the agency's formal determination that you owe additional tax, and it gives you 90 days to petition the United States Tax Court before the assessment becomes final. Missing this deadline means losing your right to challenge the amount in court without paying first.
This guide is general educational information, not professional advice. If the document involves a serious deadline, lawsuit, tax issue, health decision, or major financial consequence, get qualified help.
What this document usually means
The IRS has completed its review of your tax situation and has determined that you owe additional tax for a specific year. This notice follows earlier correspondence such as an examination report or a proposed change letter where you either did not respond or could not reach an agreement with the IRS.
The Notice of Deficiency is the IRS's statutory requirement before it can officially assess the additional tax. It starts a 90-day clock during which you can file a petition with the United States Tax Court. If you are outside the country, the deadline extends to 150 days. This is your last opportunity to dispute the tax before paying it.
The first things to check
Find the date of the notice and calculate your 90-day deadline. This is the most critical piece of information on the letter. If you miss this deadline, the IRS will assess the tax and begin collection, and your only option to dispute will be to pay first and then sue for a refund in a different court.
Review the proposed deficiency amount, including additional tax, penalties, and interest. Compare the IRS calculations against your records and any prior correspondence you exchanged during the examination process.
Check whether the notice covers all the issues you previously disputed or whether new items have been added.
Common reasons this letter feels confusing
The legal tone of the Notice of Deficiency is more formal than typical IRS correspondence. It references specific tax code sections, includes detailed computation tables, and uses language about court rights and deadlines that can feel overwhelming.
People are also confused about whether they need a lawyer to petition Tax Court. While professional representation is recommended for complex cases, individuals can file a petition on their own. Small tax cases under a certain dollar threshold have simplified procedures.
What to do before you pay or respond
If you disagree with the deficiency, file a petition with the United States Tax Court before the 90-day deadline. You can find petition forms and instructions on the Tax Court website. Filing the petition stops the IRS from assessing the tax until the case is resolved.
If you agree with the deficiency, you can sign the enclosed consent form and return it. The IRS will assess the tax and send a bill. You can then set up a payment plan if needed.
If you are unsure whether to agree or dispute, consult a tax professional immediately. The 90-day deadline cannot be extended, so time is critical. Low Income Taxpayer Clinics and tax attorneys can help evaluate whether filing a petition is worthwhile.
Do not ignore this notice. Letting the 90-day deadline pass without action means the IRS will assess the full deficiency amount and begin collection.
How Letter Lens can help
Upload your Notice of Deficiency to Letter Lens, and it will identify the deficiency amount, the 90-day deadline, and the specific items the IRS is adjusting. It translates the formal legal language into plain English so you can understand what is at stake and what action to take.
Given the legal significance of this notice, professional help is strongly recommended. Letter Lens helps you understand the letter quickly so you can seek qualified advice before the deadline passes.
Key Terms Decoded
Have an IRS Notice of Deficiency you need decoded?
Upload it now and get a plain-English explanation in seconds.
Decode It Free