IRS CP2100 notice and the B-Notice: what to do, step by step

What a CP2100 or CP2100A is

When the IRS processes your Forms 1099 (and 1098, W-2G and a few others), it matches every payee name and TIN against its records. Pairs that don't match, and TINs that are missing, are listed on a notice sent to the payer. The notice comes in three sizes, and the size determines the format, not the rules:

Notices are typically issued twice a year, in the spring and in the fall, for returns filed the previous January through March. The notice lists the payee's name, the TIN you reported, the account number if you included one, and the reason: missing TIN, or name/TIN mismatch.

Step 1: Compare the listing to your records

Before you send anything, check each listed account against your current vendor master. Publication 1281 is explicit that you should not send a B-Notice when:

• the TIN on the listing differs from the one in your records because of your own keying error, a correction you made after filing, or an IRS processing error;
• the account was already corrected and only appears because of processing lag;
• the TIN was on file but was inadvertently left off the return.

In those cases, fix the return (or your records) and move on. Sending an unnecessary B-Notice annoys a vendor for nothing and, if you begin withholding on a correct TIN, creates a refund problem you'll have to unwind.

For every remaining account, you also need to know whether this is the first or second time the same payee account has appeared on a CP2100 in the current three-calendar-year window, because the required notice is different (see below). This is why Publication 1281 tells you to track listed accounts for three years after the first notice.

Step 2: Send the first B-Notice within 15 business days

Templates for the First and Second B-Notice, following the Pub 1281 samples, are on the templates page.

For each account that still needs correction, mail the payee a First B-Notice together with a Form W-9 within 15 business days of the notice date or the date you received it, whichever is later. Publication 1281 also says to date the B-Notice no later than 30 business days after the CP2100 date, to make sure the date, the account number and the backup withholding rate are on it before mailing, and to include either a reply envelope or a return address. The outer envelope must be marked "IMPORTANT TAX INFORMATION ENCLOSED" or "IMPORTANT TAX RETURN DOCUMENT ENCLOSED". The publication says this information may not be solicited by telephone; it does not address email, so payers who deliver B-Notices electronically do it under a payee's prior consent to electronic tax documents and keep the paper route as the default.

The payee then has 30 business days from your mailing to return a signed W-9 with a name/TIN combination that resolves the mismatch. A W-9 returned on day 31 still counts for stopping withholding, but you must have begun withholding in the meantime.

Keep a copy of what you sent, the date, and the address. Sending the B-Notice satisfies one of the "annual solicitations" the IRS requires, and that solicitation history is the evidence that gets a later penalty waived.

Step 3: Start backup withholding if no W-9 comes back

If a valid W-9 hasn't arrived by the end of the 30 business days, you must begin backup withholding on reportable payments to that payee at 24%. Publication 1281 phrases the deadline from the notice side: withholding must begin no later than 30 business days after the date of the CP2100 (you may start earlier, the day after you receive the notice). Withheld amounts are deposited with your payroll or Form 945 deposits and reported annually on Form 945.

Stop withholding within 30 calendar days after the payee provides a W-9 that certifies a correct TIN (you may stop at any point in that window). Do not send the signed W-9 to the IRS, and do not file a corrected 1099 for the TIN alone; Publication 1281 says to file a correction only if a dollar amount also changes. You cannot refund amounts already withheld and deposited; the payee recovers them through their own tax return.

The second B-Notice: when a W-9 is no longer enough

If the same payee account appears on another CP2100 or CP2100A within three calendar years of the first, the IRS treats the W-9 the payee gave you as unreliable. You send a Second B-Notice, again within 15 business days, and this time you do not enclose a W-9, because a W-9 can't cure it. Instead the payee must obtain validation from the issuing agency:

• Individuals (SSN): a copy of their Social Security card, showing a different name/SSN from the one on the notice or issued within six months before the date of your second notice. Publication 1281 gives the payee instructions for contacting the SSA.
• Businesses (EIN): IRS Letter 147C, which the entity requests from the IRS Business & Specialty Tax Line and which confirms the name and EIN the IRS has on file.
• ITIN or ATIN: the payee asks the IRS for Letter 685C (ITIN) or Letter 096C (ATIN) and sends you a copy.

Backup withholding starts on the same 30-business-day schedule and continues until you receive that validation; stop within 30 calendar days of receiving it. A third or later notice for the same name/TIN combination and account can be ignored once you have completed the first- and second-notice steps; if the same payee shows up with a different name/TIN combination, that is a new first notice. Second B-Notices are where most vendor relationships get strained, because the vendor has to call the IRS or SSA and wait. The way to avoid them is to catch the mismatch after the first notice, or better, before the first payment.

The full timeline on one page

Have a notice in hand? The B-Notice deadline calculator turns the notice date into the three dates below, skipping weekends and federal holidays, and the decision tree walks each line to its action.

Mistakes that turn a notice into a penalty

• Treating it as a year-end task. The 15-day clock runs from receipt, and notices arrive in spring and fall, not in January. Someone has to own the inbox.
• Sending a W-9 with a second notice. The vendor returns it, you stop withholding, and the IRS considers the account uncorrected.
• Not tracking the three-year window. Without a record of the first notice you can't know a second one is a second one.
• Withholding on already-corrected accounts. Skipping the comparison step in Step 1 creates refunds and angry vendors.
• Fixing the TIN but not the name. The IRS matches the pair. "ACME LLC" with the owner's SSN and "John Smith" with ACME's EIN are both mismatches. Sole proprietors are the usual case: the name on line 1 of the W-9 must be the individual's name if the TIN is their SSN.
• No solicitation records. The notice itself is not the problem; the penalty notice that follows (Notice 972CG) is, and the only defense is proof that you solicited the TIN on the IRS's schedule. See the 972CG guide.

When the notices are mailed

The campus processing manual publishes the CP2100 production windows. For tax year 2025 returns the first run begins September 5, 2026 and completes October 16, 2026; the second begins April 10, 2027 and completes April 23, 2027 (IRM 3.30.123.8.5IRM 3.30.123.8.5Internal Revenue Manual, irs.gov, Jan. 1, 2026; the tax year 2024 runs were September 5 to October 16, 2025 and April 10 to April 23, 2026). The autumn run covers returns on the IRS's files by the first paper program completion date in August; the spring run picks up late and corrected filings. Two consequences: a payer that heard nothing by November is not clear until late April, and a correction filed after the original was processed can still appear on the autumn list, which is why the notice instructions tell you to compare the listing to your records before sending any B-Notice. The processing dates page has the rest of the campus calendar.

What the IRS manual adds

Three operational details from IRM 3.42.9.13IRM 3.42.9.13Internal Revenue Manual, irs.gov and IRM 20.1.7.12.2IRM 20.1.7.12.2Internal Revenue Manual, irs.gov that the CP2100 itself does not explain:

• How the notice arrives depends on volume. Fewer than 50 error documents: CP2100A with a paper listing. 50 to 249: CP2100 with paper. 250 or more: CP2100 with an encrypted CD or DVD that can only be opened with a PIN you set up on Form 10301. File the 10301 before September so the 15-business-day B-Notice clock is not spent waiting for the code; it does not need to be renewed yearly. Form 10301 walkthrough.
• There are two mailings per tax year. A staggered September and October run, and an April run the following year, plus 972CG notices in July and October. Notices are retained ten years and can be recreated on request, but not in the two weeks after a mailing date.
• The B-Notice is your annual solicitation and withholding is not the test for the waiver. Mailing it within 15 business days satisfies the solicitation requirement for the penalty; the withholding obligation is separate. An undeliverable CP2100 keeps its original date, so keep Form 8822-B current.
• The IRS will tell you whose TCC filed the returns on your notice, even if a third party transmitted them; the business name behind the TCC is your tax return information (IRM 3.42.9.13.5)IRM 3.42.9.13.5Internal Revenue Manual, irs.gov.

Full detail, with subsection citations: what the IRS will and will not do with your CP2100, and for the penalty side how the IRS judges a 972CG response.

Questions payers ask

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