A Notice of Deficiency, often called a 90-day letter or statutory notice, is the IRS's formal determination that you owe more tax. It is also your ticket to the United States Tax Court. If you file a petition in time, the IRS generally cannot assess or collect the disputed amount until the case is resolved. If you do not, the tax is assessed and collection begins.

Everything starts with reading the notice correctly. Here is what is in it and what each part means.

What makes it a Notice of Deficiency

IRC 6212(a) authorizes the IRS to send a notice of deficiency by certified or registered mail. The notice usually says "Notice of Deficiency" at the top and refers to your right to petition the Tax Court. Common versions include Letter 531, which the IRM describes as the notice letter used most often in income tax cases, and Letter 3219, commonly issued after an automated underreporter case. Estate and gift tax notices use different letters, such as Letter 902.

A 30-day letter is not a notice of deficiency. Neither is a CP2000. Neither is a balance due bill. If you are unsure, look for the Tax Court language and the petition date.

The most important line: the last day to petition

The notice states the last day to file a petition with the Tax Court. Under the final sentence of IRC 6213(a), any petition filed on or before that date is treated as timely. That protects you if the IRS computes the date generously.

The underlying rule is 90 days after the notice is mailed, or 150 days if the notice is addressed to a person outside the United States. If the last day falls on a Saturday, Sunday, or legal holiday in the District of Columbia, IRC 6213(a) says it is not counted as the last day.

Here's the part most people miss: the clock starts when the notice is mailed, not when you open it. If the envelope sat at the post office for two weeks, those were your two weeks. Check the date on the notice and the postmark. If the notice has no petition date, or the date looks wrong, do not guess. Count conservatively from the mailing date and file well before.

The deficiency and penalty amounts

The first page or two show, for each year, the deficiency in tax and any penalties or additions to tax, such as the accuracy-related penalty under IRC 6662 or the failure-to-file addition under IRC 6651. Interest is generally not shown as part of the deficiency; it is computed separately.

Write these numbers down by year. They matter for two decisions: whether the case qualifies for small tax case procedures under IRC 7463, which caps the amount in dispute at $50,000 per year including penalties, and how much is at stake in each year if you consider settlement.

The attachments

The notice usually includes several forms, and each one tells you something:

  • Form 4089 or 4089-B, Notice of Deficiency Waiver. Signing it agrees to immediate assessment. Do not sign it unless you have decided not to contest the deficiency.
  • Form 4549-A or Form 5278, the statement of income tax changes. The line-by-line computation of how the IRS got from your return to its number.
  • Form 886-A, Explanation of Items. The narrative explanation of each adjustment. This is where you learn the IRS's theory.

Read the Form 886-A twice. Your petition will need to assign error to each adjustment you dispute. Under Tax Court Rule 34(b)(1)(G), any issue not raised in the assignments of error is deemed conceded.

The Taxpayer Advocate notice

IRC 6212(a) requires the notice to tell you of your right to contact a local office of the Taxpayer Advocate and to give its location and phone number. The Taxpayer Advocate Service can help with IRS process problems. It does not extend the 90 days.

Who the notice was sent to

Check the name and address. Under IRC 6212(b), a notice mailed to your last known address is sufficient even if you never receive it. If it was sent to an old address, or to only one spouse on a joint return when the IRS had been told you lived apart, there may be a validity issue. See invalid notices of deficiency. Do not let that question delay a petition. Petition first; argue validity later if it matters.

Common misreadings

  • "The IRS gave me 90 days to pay." No. The 90 days are to petition the Tax Court. Payment is a separate question.
  • "I already sent a protest, so I am covered." A protest to Appeals does not substitute for a petition once a notice of deficiency is issued.
  • "The amount is wrong, so the notice is invalid." An incorrect amount is a reason to petition, not a defect that voids the notice.
  • "I can call and explain." A phone call does not stop the clock. Only a timely petition protects your right to contest without paying first.

Your options, in order of consequence

  1. Petition the Tax Court. This preserves your right to contest without paying first. Most petitioned cases are referred to IRS Appeals for settlement consideration if Appeals has not already considered them. See how to file the petition.
  2. Agree and sign the waiver. The tax is assessed, interest stops growing on the amount you pay, and collection follows if you do not pay.
  3. Do nothing. Under IRC 6213(c), the deficiency is assessed after the period expires. You can still pay and sue for a refund in district court or the Court of Federal Claims, but the full payment rule generally requires paying the assessed tax first.
  4. Ask the IRS to reconsider while you prepare a petition. You can send information to the office that issued the notice, but that does not stop the clock. A rescission is possible in limited cases and only with IRS agreement.

The first week checklist

  • Find the mailing date and the last day to petition. Calendar both.
  • Pull your account transcripts for each year on the notice.
  • Gather the audit file: the 30-day letter, the examination report, your protest if you filed one, and your correspondence.
  • List each adjustment on Form 886-A and mark which ones you dispute.
  • Decide on regular or small case procedure.
  • Talk to counsel before you send the IRS anything new.

The firm's article on building a statutory notice of deficiency action plan is a useful companion to this page.

Let's talk

Ninety days sounds like a lot until you spend thirty of them deciding what to do. If you are holding a Notice of Deficiency, call (813) 229-7100. Let's talk about the petition while the date is still comfortably ahead of you.