CP2100 Notice: What It Means And How To Respond

A CP2100 notice isn’t an audit, and it isn’t a penalty. It means the IRS found a name and TIN combination on your 1099 filings that doesn’t match its records. You get a set window to fix your records, tell the affected payees, and start backup withholding if they don’t respond. Hit those deadlines and the notice closes quietly. Miss them and the IRS can propose a penalty months later. The steps are simple. The deadlines are strict.

What is a CP2100 notice?

A CP2100 notice is a letter from the IRS telling a business that one or more payee names and taxpayer ID numbers on its filed 1099s don’t match IRS or Social Security Administration records. It lists the flagged payees and the numbers you reported. It’s a warning to fix your records, not a bill.

The IRS sends two versions. You get a CP2100 if 50 or more of your returns had errors. You get a CP2100A if fewer than 50 did. The instructions and the required response are the same, and the IRS confirms that the only real difference is the number of error returns behind the notice.

Why did you get one?

Because a payee’s name and number didn’t line up with federal records. The usual causes are ordinary. A contractor wrote the wrong EIN on a W-9. Someone transposed two digits during data entry. A person married and changed their name with one agency but not the other. And the most common case of all: a sole proprietor put their business (DBA) name on line 1 of the W-9 instead of their legal name. The IRS matches line 1 against the legal name on file with the SSA, so the business name fails the check.

When does the IRS send CP2100 notices?

Twice a year, in October and again the following April. October notices cover returns processed earlier that year. April notices pick up corrected filings and late arrivals. So a 1099 you filed in January 2026 would show up on an October 2026 notice if it had a mismatch. A correction you sent in March could surface the next April.

First and second B-notices: who sends them?

You do, not the IRS. This one trips up almost everyone. A “B-notice” (backup withholding notice) is a letter you mail to the payee after the IRS flags them. There are two kinds, and the difference is where the money gets lost.

	First B-notice	Second B-notice
When to send	Payee’s first time on a CP2100 in a 3 calendar year period	Same payee’s second time within 3 calendar years
Include a W-9?	Yes, a blank one	No
What the payee must do	Return a signed W-9 with the correct name and TIN	Send official proof: a copy of their Social Security card (individuals) or IRS Letter 147C (businesses)
Deadline to mail	15 business days from the notice date or receipt, whichever is later	Same, 15 business days

A W-9 does not fix a second B-notice. That’s the single most expensive mistake in this whole process. On a second notice, the payee has to verify their number straight from the source: the SSA for individuals, or the IRS for a business EIN. Accept another self-signed W-9 and the mismatch is still sitting there, and the next CP2100 is already on its way.

Here’s a rule people also get backwards: two notices in the same calendar year count as one. If the same payee shows up twice inside one calendar year, you send one B-notice, not two. A payee only moves to “second notice” status when the second appearance lands in a different calendar year within the three-year window. You track this yourself, and the IRS won’t tell you whether a payee is on strike one or strike two. If the count gets murky, a Michigan tax attorney can confirm which notice applies.

One small step with big consequences: mark the outside of every B-notice envelope “IMPORTANT TAX INFORMATION ENCLOSED” or “IMPORTANT TAX RETURN DOCUMENT ENCLOSED.” That wording is an IRS rule spelled out in Publication 1281, not a suggestion. A perfect letter in a plain envelope doesn’t count.

The backup withholding clock (2026 rate: 24%)

If a payee ignores your B-notice, you have to hold back 24% of their future payments and send it to the IRS. Backup withholding is the enforcement tool: if someone won’t give a correct TIN, the IRS collects the tax at the source instead. These are the deadlines that actually matter.

Action	Deadline
Mail the B-notice	Within 15 business days of the CP2100 date or the date you got it, whichever is later
Start 24% backup withholding (no response)	By the 30th business day after the CP2100 date or receipt, whichever is later
Stop backup withholding (valid response)	Within 30 days of getting a valid W-9 or official TIN certification
Report what you withheld	On Form 945, Annual Return of Withheld Federal Income Tax

The rate is 24%. If your written procedures still say 28%, they’re stale; that rate ended after 2017, and using it is a common slip in offices that never updated the template. Deposit what you withhold on the schedule that fits your size, monthly or semiweekly, under the rules in IRS Publication 15.

One useful exception: if a payee never responds and you make no more payments to them, you owe no backup withholding. There’s nothing left to withhold from. Just keep proof that you mailed the notice and got no answer.

Missing TIN or wrong TIN? Two different tracks

These aren’t the same problem, and the fix is different. If a payee never gave you a TIN, or gave one that’s obviously wrong (not nine digits, or with a letter in it), you start backup withholding right away and make up to three requests for the number: one when you open the account, then two annual follow-ups. That solicitation record is what protects you from a separate missing-TIN penalty. The B-notice steps above are for the other case, where you have a number but it doesn’t match. Don’t run one playbook for both.

Does filing through IRIS change anything?

Fewer surprises, but not zero. The IRS is retiring its old FIRE system and moving electronic 1099 filing to IRIS. Starting with tax year 2025 returns, IRIS runs a name and TIN check at submission, so a mismatch can bounce back the same day as an “Accepted with Errors” status (IRIS error 015 flags a business name and EIN that don’t agree). That beats the old days, when the first sign of trouble was a CP2100 months later.

But IRIS doesn’t end CP2100 notices. The IRS runs its own match after processing, and it can flag records IRIS waved through. Treat the submission check as a first filter, not a force field. You can still get a CP2100 on a return IRIS accepted, so the response steps above still matter.

What happens if you ignore it: Notice 972CG

Do nothing and the IRS can send a 972CG, a proposed penalty notice, usually about a year later. It attaches a dollar figure to the returns that stayed wrong, based on how many and how long. You get 45 days to respond before it’s final and collection starts.

This is the part software won’t do for you, and the part worth getting right. You can ask the IRS to drop or cut the penalty for reasonable cause. The argument that works isn’t “we were busy.” It’s proof that you acted responsibly: that you mailed the B-notices on time, asked for correct TINs, and kept records of every step. Under the reasonable-cause rules (Treasury Regulation 301.6724-1) that sit behind the IRS information return penalty program, a clean paper trail plus a real reason the failure was outside your control is what moves the IRS. A well-built reasonable-cause letter can remove or sharply reduce the penalty, which is why this is where a business tax attorney or enrolled agent earns the fee.

How to stop the next one

Fix the data before you file, not after a notice lands. Three habits head off most CP2100s:

• Collect a W-9 before the first payment, not after. Make it part of onboarding. Chasing one later is how records go stale.
• Run the free IRS TIN Matching program before filing season. It checks name and TIN combinations against IRS records so you can fix them while there’s still time.
• Re-check recurring vendors once a year. Names change, EINs get reassigned, people marry. A vendor who matched last year may not match this year.

Watch sole proprietors closely. The legal name goes on line 1 of the W-9, the business name on line 2. Getting that one field right heads off the most common mismatch there is, and the same IRIS error at filing.

Get help before the penalty, not after

A CP2100 notice is manageable on your own if you hit the deadlines and keep records. The moment it turns into a 972CG penalty, or you can’t tell whether a payee is on their first or second strike, it’s worth calling a tax professional who handles IRS notices and penalty relief. Acting inside the 45-day window is far easier than fighting a penalty after it’s assessed. If you’d rather hand the whole thing off, Austin & Larson Tax Resolution can take it from there. In the end, a CP2100 notice rewards the businesses that move fast and write everything down.

FAQs

Is a CP2100 notice an audit?

No. A CP2100 notice is a name and TIN mismatch warning on your 1099 filings. It isn’t an audit and carries no penalty on its own. It only becomes a penalty risk if you skip the required steps.

What’s the difference between a CP2100 and a CP2100A?

Volume. You get a CP2100 if 50 or more of your returns had errors and a CP2100A if fewer than 50 did. The content and the required response are identical.

What is the backup withholding rate in 2026?

24% of the reportable payment. The old 28% rate ended after 2017. You report the amounts you withhold on Form 945.

Do I send a Form W-9 with a second B-notice?

No. A second B-notice requires the payee to verify their TIN with the SSA (a copy of their Social Security card) or the IRS (Letter 147C for a business). A new W-9 doesn’t satisfy a second notice.

How long do I have to respond to a CP2100 notice?

Mail your B-notices within 15 business days of the notice date or the date you received it, whichever is later. Start 24% backup withholding by the 30th business day if the payee hasn’t responded.

What is Notice 972CG?

It’s the IRS proposed penalty notice for uncorrected 1099 errors, usually sent about a year later. You get 45 days to respond, and you can ask for relief for reasonable cause if you documented your correction efforts.