What Is a CAF Number and How Do You Get One?

If you're filling out Form 2848 or Form 8821 for the first time and hit the box that asks for a CAF number, here's the short version: it's an ID the IRS assigns to you personally, not to your firm, the first time you're authorized to act on a client's behalf. You only get one, ever, and you'll use the same one on every authorization form for the rest of your career.

What CAF actually stands for and what it's for

CAF stands for Centralized Authorization File. It's the IRS's internal system for tracking who's authorized to represent which taxpayer, and for what purposes. Every time you file a Form 2848 (Power of Attorney) or Form 8821 (Tax Information Authorization), the IRS logs that authorization against your CAF number so their staff can quickly verify, when you call or when they're reviewing a return, that you're actually allowed to be talking to them about that client.

Without a valid authorization tied to your CAF number on file, the IRS can't discuss a client's account with you at all, even if the client is sitting right next to you on the phone.

You don't apply for a CAF number separately

This trips people up: there's no standalone application form for a CAF number. You get one automatically, generated by the IRS, the first time you submit a properly completed Form 2848 or Form 8821 that doesn't already have a CAF number on it. The IRS processes the form, assigns your number, and mails it to you (typically within a few weeks, though processing times shift depending on filing volume). From that point forward, you use that same number on every future authorization.

The mistake that delays everything

The most common holdup isn't the CAF number itself. It's submitting an authorization form with a mismatch between the practitioner's name, address, or other identifying details and what the IRS already has on file, which kicks the form back for correction and resets the clock. Before you submit, double-check that your name and address on the form exactly match your professional registration details (PTIN records, if you have one), since small mismatches are the single biggest cause of processing delays.

What to put on the form your first time

If you genuinely don't have a CAF number yet, leave that field blank rather than guessing or writing "none" in a way that confuses the form's formatting. The IRS will generate one automatically once the form processes. If you're not sure whether you already have one (this happens with staff who've moved between firms), check any prior authorization paperwork or reach out to the IRS Practitioner Priority Service line, since submitting a form with the wrong CAF number listed causes more delay than leaving it blank.

Where this fits into onboarding a new client

For firms handling any IRS correspondence work, getting the authorization filed correctly and promptly is usually one of the first things that needs to happen after a new client signs on, especially if there's an active notice or deadline involved. Firms that track this as a formal step (request sent, signed, filed, confirmed) tend to catch delays early. Firms that handle it informally over email are the ones who discover three weeks later that the form never actually got submitted.