What it means
The IRS has determined you owe more tax, often after a CP2000 or a substitute return. This letter gives you the right to challenge it in Tax Court.
What to do now
Get help immediately. If you disagree, a petition to the U.S. Tax Court must be filed before the deadline, or the IRS can assess the tax.
Deadline
90 days from the notice date to petition Tax Court (150 days if addressed to you outside the U.S.). This deadline can’t be extended. Always go by the date printed on your notice.
Last updated October 15, 2026.