Every IRS notice, in plain English.
What each one means, the deadline it actually carries, the rights that expire with it, and the mistake people make. Two things separate this from the rest of the internet. Every claim is cited to the IRS, the Internal Revenue Manual or the Code. And where the IRS publishes no day count — which is most of them — we say so instead of repeating the thirty days that circulates without a source.
A Notice of Deficiency — CP3219A, Letter 531 or Letter 3219 — gives you 90 days from the date it was mailed, or 150 if it was addressed to someone outside the United States, to petition the Tax Court. The IRS states on its own page that replying to it does not extend that time. Every other deadline in this library is softer than it looks; that one is harder. What to do with one →
The IRS spots a mismatch
It proposes a change
It makes the determination formal
It bills you
It starts collecting
The consequences reach beyond tax
Everything else
Questions people actually ask
Which of these actually has a deadline that cannot be moved?
One: the Notice of Deficiency — CP3219A, Letter 531 or Letter 3219. Ninety days from the date it was mailed, a hundred and fifty if it was addressed outside the United States, and the IRS says plainly on its own page that talking to it during that window does not extend the window. The CP2000 deadline before it can be extended; this one cannot.
Why do some of these pages say there is no deadline when everyone else says 30 days?
Because the IRS does not publish one for those notices, and we would rather say that than repeat a number we cannot source. For CP2501, CP15, CP501, CP503, CP23, CP49, CP71 and the identity-verification letters, the IRS says only 'by the date shown on your notice'. The date on your copy is the one that governs — and if a site tells you 30 days with no citation, it is guessing on your behalf.
Which notice is the last one with a court at the end of it?
For a proposed tax change, the Notice of Deficiency — that is your Tax Court ticket. For collection, the final levy notice: CP90, LT11 or Letter 1058. Thirty days, Form 12153, and a Collection Due Process hearing you can take to the Tax Court afterwards. File it on day 31 and you get an Equivalent Hearing instead, which feels the same and has no court at the end.
Is a CP504 a final levy notice?
No, despite the wording. On its own it supports a levy on your state income tax refund, and it carries no Collection Due Process right — which is why it does not appear on the IRS's own list of notices offering that appeal. Filing Form 12153 against a CP504 preserves nothing. The final notice is the one that comes next.
What does any of this have to do with crypto?
The underreporter notices — CP2501 and CP2000 — are the ones a crypto 1099 produces. Brokers report your proceeds and leave the cost box blank, so the proposal computes the tax as though your coins were free. In Notice 2026-20 the IRS acknowledged that broker-reported basis and your own records will not match for 2026 transactions, and that where you made an adequate identification in your books and records, those records control regardless of what the broker reported. Reconstructing them is the answer to the notice.
Most crypto notices are arithmetic, not accusation.
The exchange reported what you sold for and left the cost box blank, so the IRS computed the tax as though the coins were free. Rebuild the basis from your own transaction history — free — and answer with a number instead of an apology.