B notice timeline.

What the notices are

The IRS sends a payer a CP2100 or CP2100A notice when payee names and TINs on information returns do not match its records. The payer then sends the payee a “B” notice, which is a backup withholding notice. There are two. You send the First B notice with a Form W-9 after the first CP2100 or CP2100A for an account. You send the Second B notice, which has different text and does not include a W-9, after a second notice within three calendar years. The second one tells the payee to get the correct name and TIN combination from the IRS or the Social Security Administration, and you must receive that validation from the SSA or IRS.

The clock

Backup withholding is currently 24 percent, taken from future reportable payments. The mailing envelope must be clearly marked “IMPORTANT TAX INFORMATION ENCLOSED” or “IMPORTANT TAX RETURN DOCUMENT ENCLOSED.” If a B notice comes back undeliverable you must begin backup withholding, try to find the correct address and remail it, and keep the undelivered notice for three years to track the two-in-three-year rule.

When you do not mail a second B notice

The IRS FAQ says you do not have to mail a second B notice if the second CP2100 or CP2100A arrives in the same calendar year as the first, even if it relates to a different tax year, and you also do not need to if the notices arrive in different calendar years but both relate to the same payee account for the same calendar year. Generally you do not have to send a B notice more than twice in three calendar years to the same account.

Counting business days

The tool counts Monday through Friday after the notice date. Pub. 1281 uses the phrase “business days” without listing holidays, so a legal holiday inside the window can only push your actual deadline later, never earlier. Use the dates as the earliest the clock can run out.

Worked example

Cedar Street Brokerage receives its first CP2100 dated Monday, November 2, 2026, listing a mismatched payee. Fifteen weekdays later is Monday, November 23, 2026, the day by which the First B notice and a W-9 must be mailed. Thirty weekdays later is Monday, December 14, 2026, the latest day to begin withholding 24 percent unless the payee has returned a certified W-9. The payee returns the W-9 on December 1; backup withholding, if started, must stop within 30 calendar days of that receipt.

Who is subject to this

These steps are for payers of reportable payments. If you are the payee who got a B notice, see the IRS backup withholding page and Form W-9; the W-9 classification page shows how to complete the form correctly and the exempt payee code page shows who is exempt.

Sources

• Publication 1281, Backup Withholding for Missing and Incorrect Name/TIN(s) (Rev. 12-2023): FAQ questions 14 to 20: B notices, the 15 and 30 business day deadlines, undeliverable notices and stopping withholding. Read November 2, 2026.
• IRS: Backup withholding: The 24 percent rate, BWH-B and BWH-C programs, payments subject to and excluded from backup withholding. Read November 2, 2026.

IRS backup withholding page last reviewed October 10, 2026. Pub. 1281 is the December 2023 revision.