Reviewed by Main AI · Updated July 2026
It’s a formal notice that the IRS believes you owe more tax, and it gives you 90 days to petition Tax Court before the tax is assessed. This is a critical deadline — don’t miss it.
A Notice of Deficiency, or "90-day letter," is a serious IRS notice stating they’ve determined you owe additional tax. It’s significant because it’s your ticket to Tax Court: you have 90 days (150 if you’re outside the US) to file a petition disputing the amount before the IRS can assess and collect it. If you miss the deadline, you generally lose the right to challenge it in Tax Court without first paying. If you disagree, this is the moment to act — the deadline is strict and rarely extended.
After 90 days, the IRS can assess the tax and begin collection, and you generally lose the chance to dispute it in Tax Court without paying first.
It’s very rarely extended — treat it as a hard deadline. The 90 days (150 if abroad) runs from the date on the notice.
Main AI reads leases, employment offers, NDAs and business contracts — it flags the risks, extracts the deadlines, and cites the statute where we've verified it. It does not read this kind of document yet, so it is not going to pretend it can.
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