What Is Backup Withholding and How to Avoid It

What backup withholding is

Under IRC §3406, payers must withhold 24% from certain payments when a payee does not provide a correct taxpayer identification number, when the IRS notifies you of a TIN/name mismatch (CP2100 or related notices), or when the payee checks the box on Form W-9 certifying they are subject to backup withholding. It is not optional penalty withholding — it is a statutory obligation once conditions are met.

Payments subject to backup withholding

Backup withholding commonly applies to reportable payments such as rents, royalties, commissions, fees for services, and other amounts you would report on Form 1099. It generally does not apply to wages (reported on W-2) or to payments to corporations in many cases, though exceptions exist — including when the corporation is subject to notification of mismatched TINs.

• Independent contractor payments (1099-NEC)
• Rent and royalty payments (1099-MISC and related)
• Broker and barter exchange transactions in scope
• Interest and dividends in certain payer contexts

How the W-9 prevents withholding

Form W-9 collects the payee's TIN and their certification under penalties of perjury that the TIN is correct, they are not subject to backup withholding (unless the box is checked), and they are a U.S. person. A complete, signed W-9 on file before payment is your primary defense — provided the TIN and name actually match IRS records.

CP2100 and B-notice obligations

When the IRS identifies TIN/name combinations that do not match its database, you may receive a CP2100 or CP2100A notice listing payees with proposed mismatches. You must send a B-notice (solicitation for corrected information) to affected payees and begin backup withholding if they do not respond within the required timeframe. Document every notice, vendor outreach, and withholding start date — auditors will ask.

Operational mistakes that trigger withholding

AP teams sometimes create their own exposure: accepting W-9s with missing TINs 'temporarily,' ignoring failed TIN matches, using invoice DBA names on 1099s instead of W-9 legal names, or continuing payments after a B-notice deadline without withholding. Each of these turns a fixable onboarding gap into a withholding and reporting problem.

Building backup withholding into your process

Validate TINs at W-9 intake, block payments when certification is incomplete, maintain a B-notice response log, and configure ERP or AP systems to flag payees under active withholding. When withholding applies, remit deposits on schedule and report on Form 945. A monitored W-9 workflow catches gaps before the IRS does.