Somebody holding an IRS letter usually wants one thing first: to know which letter it is. There are hundreds of them and they range from a corrected figure to a serious proposal to change your return.
There is a number that answers it, and the IRS prints it in the same place every time.
It is on the right
In the IRS’s own words: “You can find the CP or LTR number on the right corner of the letter.”
That is the identifier. Not the amount, not the date, not the office it came from. If you are going to write one thing down before doing anything else, write that.
CP and LTR
You will see one of two prefixes.
CP is a computer generated notice. The IRS’s systems produced it automatically because something on your account met a condition: a balance, a changed refund, a delay, a mismatch between what was filed and what a third party reported.
LTR is a letter, generally produced in the course of something a person is handling.
Neither prefix tells you how serious the contents are. A CP notice can be trivial or significant. The number after it is what narrows it down.
Look the number up, not the city
A lot of people search for the city printed on the envelope instead, trying to work out what is coming.
It will not tell you. The city is where the letter was processed, not what it concerns. The same processing location handles many unrelated kinds of correspondence, and two people holding letters postmarked from the same city can be dealing with completely different things.
The number is specific. The city is not.
Once you have the number, the IRS has a search on its own site for looking it up. And if the letter does not appear there, or if anything about it seems off, the IRS asks you to call 800-829-1040 rather than respond to it.
What people mean by an access code
This comes up often enough to be worth naming. People search for an access code on an IRS letter, and usually one of two things is meant.
Most of the time it is the notice number described above: the thing you need in order to look the letter up. That is the number in the right corner.
Sometimes it is a code printed on a letter asking you to confirm your identity, used once to complete that specific process. Those letters say plainly what the code is for and where to use it.
Either way the instruction is the same: use it only on the route the letter itself describes, and only after you are satisfied the letter is genuine. A code is exactly the sort of thing an impersonation attempt wants you to hand over.
Before you respond
Two things worth doing once you have the number.
Check the deadline. It is on the letter, and most of your options depend on it.
Check whether it is right. A notice is what the IRS currently believes about your account. Where a notice proposes a change to your return, agreeing by default is a decision, not a formality.
If you are not sure which of those you are looking at, bring it in. Reading a notice number and knowing what it actually means are two different jobs, and the second one is quick when you do it every week.