Getting a Notice of Deficiency from the IRS can feel like the moment a tax issue becomes very real. Many taxpayers open the envelope, see proposed additional tax, penalties, or both, and immediately wonder whether the IRS has already won, whether payment is due right away, and whether there is still time to push back.
In general terms, a Notice of Deficiency is the IRS’s formal notice that it believes additional tax is owed and that the taxpayer has a limited window to ask the U.S. Tax Court to review that determination before paying. The IRS and the Taxpayer Advocate Service often describe it as the taxpayer’s “ticket” to Tax Court, and federal law generally gives taxpayers 90 days from the mailing date to file a petition, or 150 days if the notice is addressed to a person outside the United States. The deadline rules come from Internal Revenue Code § 6213, and the IRS and Tax Court repeat those rules in their current guidance (IRS, Taxpayer Advocate Service, U.S. Tax Court).
In this post, you’ll learn the 10 questions taxpayers ask most often after receiving a Notice of Deficiency, what those questions usually mean in plain English, and where legal help may become especially valuable.
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A Notice of Deficiency is a formal IRS letter stating that the agency has determined a tax deficiency for one or more years. It is often called a statutory notice of deficiency or a 90-day letter. The IRS uses it to explain proposed adjustments and give the taxpayer a path to challenge them in the U.S. Tax Court before payment. The Taxpayer Advocate Service uses similar language and describes the notice as the document that opens the door to Tax Court review (IRS CP3219A page, Taxpayer Advocate Service).
This is different from many earlier IRS letters. A CP2000, for example, is usually a proposed underreporter adjustment, not yet the formal notice that starts the Tax Court petition clock. If the dispute continues, the IRS may later issue CP3219A or another statutory notice. The IRS explains that progression in its current materials about return reviews by mail and proposed changes (IRS Publication 5181, IRS CP2000 explainer).
For readers who want a fuller look at what happens once a deficiency case reaches court, this overview of how Tax Court deficiency cases work before payment can help connect the notice to the larger process.
Usually, not immediately in the collection sense. A Notice of Deficiency is generally a proposed determination, not yet a final bill that can be collected through normal assessment and levy procedures. Under 26 U.S.C. § 6213, the IRS generally cannot assess the deficiency or begin collection during the 90-day or 150-day petition period, and if a timely Tax Court petition is filed, collection is generally paused until the Tax Court’s decision becomes final.
That said, many taxpayers are surprised to learn that even when immediate collection is paused, interest can continue to accrue on unpaid amounts, and the IRS explains that underpayment interest generally runs until the balance is paid in full. The IRS also notes that interest commonly continues on unpaid tax, penalties, and even interest itself in some circumstances (IRS interest guidance, IRS Topic No. 653).
Here’s what this often means in practical terms: the notice may not require instant payment, but it often creates a short window to decide whether the proposed tax is accepted, disputed administratively, challenged in Tax Court, or addressed through some other path. An attorney or tax controversy professional may help evaluate which route fits the facts and the deadline.
For many taxpayers, this is the most important question.
Federal law generally provides 90 days from the date the notice was mailed, or 150 days if the notice is addressed to a person outside the United States, to file a petition in U.S. Tax Court. The statute also says that if the last day falls on a Saturday, Sunday, or legal holiday in the District of Columbia, that last day is not counted as the deadline day (26 U.S.C. § 6213).
The U.S. Tax Court’s current filing page adds an important procedural detail: for electronic filing, the Court generally states that it must receive the petition no later than 11:59 p.m. Eastern Time on the last date to file (U.S. Tax Court eFiling guidance). That timing point can matter for taxpayers filing from another time zone or filing at the last minute.
The Taxpayer Advocate Service and IRS materials also repeat the 90-day and 150-day framework and emphasize that the date on the notice matters (Taxpayer Advocate Service filing guidance, IRS Taxpayer Bill of Rights material).
Because jurisdiction in Tax Court often turns on timely filing, many taxpayers in this situation look for legal help quickly, especially when the notice has been sitting unopened, was mailed to an old address, or involves multiple tax years.