Notice of Deficiency (CP3219A): the letter with a real deadline

I've written before about ordinary balance-due letters. This one is different, and mistakes here cost more.

How it differs from a CP2000

A CP2000 is a proposal: the IRS suggests a change, and you can agree or object without rushing. A CP3219A comes when no response to the CP2000 was filed or the response wasn't accepted. It's a formal determination.

Why the deadline is strict

You have 90 days (150 if you're outside the US) to petition the US Tax Court. Miss it, and the proposed amount becomes an official debt that can only be challenged after you pay, through a refund suit.

The main trap

The letter looks like one more notice in a long exchange. In fact it's the last point where you can disagree without paying first.

What to do when you receive it

Find the line "Last day to file a petition with the U.S. Tax Court". That's your deadline. The 90 days run from the date the letter was mailed, not the date you received it, and mail delays don't extend it. Don't call instead of responding in writing: a phone call doesn't stop the clock.