What is a CAF number?
Centralized Authorization File number
Short answer
A CAF number is the IRS file number assigned to a representative the first time a Form 2848 or 8821 naming them is processed, and used on every later form.
What it is
The Centralized Authorization File is the IRS database of third-party authorizations. When the IRS processes a Form 2848 or 8821 for a representative who does not yet have a number, it assigns a CAF number, and that number identifies the representative on all future forms.
A CAF number is not a credential and does not mean the IRS has vetted the person. It is a filing key, like an account number.
Why it matters for a tax firm
Forms with a missing or mistyped CAF number are rejected or delayed. Keep the number with the firm's PTIN and EFIN records and use it consistently, including the same name format.
Related terms
Read more on XyloDocs
Sources
Questions about CAF number
How do I get a CAF number?
You do not apply for one. Write "none" in the CAF box on your first Form 2848 or 8821; the IRS assigns the number when it processes the form and mails it to you.
Does a CAF number expire?
No, but it can be deactivated if the IRS cannot match you to it or if practice rights are lost. Use it at least once in a while and keep your contact details current.
Last reviewed: October 16, 2026. This glossary explains terms; it is not legal or tax advice. Check the cited source for the current rule.
Stop chasing documents and status calls
XyloDocs is the AI client communication platform for tax firms: bilingual calls and texts, document intake over WhatsApp and email, and status updates clients read before they phone.