Understanding IRS Notice CP09: Notice of Proposed Adjustment and How to Respond
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What the IRS Is Telling You
This notice informs you that the IRS has identified a discrepancy on your tax return and proposes to adjust your tax liability. You have 30 days to respond with documentation supporting your original position.
The Detangler: Plain English
"The IRS thinks you screwed something up on your return. They're giving you a chance to prove them wrong before they assess the tax. Don't ignore this."
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Last Verified: May 10, 2026