When you receive an IRS notice, look in the top right hand corner to find the notice number. The notice should cover a specific issue about your account or return. Below are some common notice numbers and the reason for the correspondence or letter.

CP 11:
Changes to your tax return, there is a balance due. During processing your return, the IRS made changes and there is a balance due now.

CP 14:
Balance due. This is not a math error notice, it show the amount of underpaid tax according to their records.

CP 22E:
Examination Adjustment Notice, Balance Due. This notice shows there was an exam adjustment done to your return.

CP 31:
Your refund check was returned. You should update your address, it was sent to your last address on file.

CP49:
Overpaid tax applied to other taxes you owe.

CP 90/CP 297:
This notice is telling you the IRS is intending to issue a levy against any federal payments due you. The IRS may also file a tax lien if they have not already done so. You have 30 days from the date of the notice to contact the IRS before they issue a levy.

CP 297A:
This notice is telling you the IRS has issued a levy against any federal payments due you.

CP 91/CP 298:
Final Notice Before Levy on Social Security Benefits

CP 161:
Request for Payment or Notice of Unpaid Balance Due

CP 501:
Reminder Notice- Balance Due

CP 503:
Second Notice- Balance Due

CP 504:
Final Notice Intent to Levy. This notice is letting you know the IRS intends to levy against your state refund and is looking for other assets to levy

CP 523:
Notice of Default on Installment Agreement. This notice is letting you know the IRS has terminated your Installment Agreement. The notice should tell you the specific reason, it could be that you missed a payment, you have a new balance due or you did not file a required tax return.