Where to Find the Letter Number
Every piece of IRS correspondence has an identifying number. For notices, it starts with "CP" followed by a number. For letters, it starts with "LTR" followed by a number and sometimes a letter suffix. This code tells you exactly what the IRS is communicating and what action they expect from you.
Look in the upper right corner of the first page. You will see something like "Notice CP14" or "Letter 525" or "LTR 1058." Some letters also have a suffix like "C" after the number. The suffix usually indicates a variant or a specific version of that letter type.
CP Notices vs. LTR Letters
CP notices are computer-generated. They come out of the IRS automated systems and typically deal with account adjustments, balance due reminders, and processing issues. They are usually sent from IRS service centers and do not have a specific person assigned to your case.
LTR letters are generated by specific IRS functions or employees. They tend to be more targeted and may come from examination, collection, appeals, or other divisions. A Letter 525 means an auditor is proposing changes to your return. A Letter 1058 means a revenue officer or automated collection system is about to levy your assets.
The LT Series
There is also an "LT" series, which stands for "Letter Taxpayer." These are collection-oriented letters that often deal with balance due reminders, levy notices, and installment agreement communications. LT11, for example, is a final notice of intent to levy that triggers Collection Due Process hearing rights.
Why the Number Matters
The letter number is the single most important piece of information on the page. It tells you whether you are dealing with a routine account notice or a life-altering legal deadline. A CP14 is a balance due notice that gives you time to respond. A CP90 is a final levy notice that gives you exactly 30 days to protect your rights. Knowing the difference can save you thousands of dollars and years of stress.
When you call a tax professional for help, the first thing they will ask is the letter or notice number. Have it ready. It tells them everything they need to know about where your case stands and what needs to happen next.
Common Formatting Variations
Some letters include revision dates at the bottom. Some have multiple pages with different codes on continuation pages. Always use the code from the first page of the letter. If the letter references a prior notice, note both numbers so your tax professional can trace the full history of IRS communications on your account.
The letter number is your roadmap. It tells you what the IRS wants, what your rights are, and how much time you have to respond. Find it first, research it second, and respond before the deadline.