Try it now, capture a real invoice
Free plan · No credit card · Your data stays yours
Backup withholding is a rule that forces you to hold back 24% of what you owe a vendor and send it to the IRS instead of to the vendor. It applies when a payee has not given you a valid taxpayer identification number, or when the IRS tells you the number they gave you is wrong. For an accounts payable team, it is not a tax question so much as a vendor-onboarding question: get a signed W-9 with a correct TIN before the first payment and backup withholding never becomes your problem.
What is backup withholding?
Backup withholding is the IRS's insurance policy against income that gets paid out but never reported. Most business-to-business payments are not taxed at the source. You pay a contractor their full fee, they report it, they pay their own tax. That system only works if the IRS can match the payment to a real taxpayer, and the taxpayer identification number is the link.
When that link is missing or broken, the IRS shifts the collection burden onto you, the payer. You withhold 24% of each reportable payment, deposit it with the IRS, and pay the vendor the remaining 76%. The withheld money is credited against the vendor's tax bill, so it is not a penalty on them, but it is an unpleasant surprise if they were not expecting it, and it is a real compliance liability for you if you were supposed to withhold and did not.
What triggers backup withholding?
There are a handful of triggers, and two of them are the ones AP actually runs into:
- No TIN provided. The vendor never returned a W-9, or returned one with the TIN field blank. This is the single most common trigger and it is entirely preventable.
- An obviously invalid TIN. The number is not nine digits, or it contains characters that are not numbers. You do not need the IRS to tell you this one is wrong.
- The IRS says the name and TIN do not match. You get a CP2100 or CP2100A notice listing payees whose name and TIN combination failed the IRS match. You then send the vendor a B notice asking them to fix it.
- The IRS notifies you of underreporting. This applies to interest and dividends rather than the trade payables most AP teams handle.
- The payee failed to certify they are not subject to backup withholding. That certification is part of the W-9 itself.
What is the backup withholding rate?
The backup withholding rate is 24% of the reportable payment. It has been 24% since the 2017 tax law set it there, and it remains 24% for 2026. There is no sliding scale and no gross-up: you take 24% off the amount you would otherwise report on a 1099 and remit it.
| Item | Detail |
|---|---|
| Rate | 24% of the reportable payment |
| Form you collect | Form W-9 from every US vendor |
| Form you file | Form 945, annual return of withheld federal income tax |
| Where it shows up | Box 4 of the vendor's 1099-NEC or 1099-MISC |
| Triggering notice | CP2100 or CP2100A from the IRS |
| Your response to the vendor | A B notice requesting a corrected W-9 |
How the $2,000 threshold changed things in 2026
Under the One Big Beautiful Bill Act, the reporting floor for most 1099 payments rose from $600 to $2,000 for payments made on or after January 1, 2026, and that same floor now governs when backup withholding kicks in on those payments. In practice, that means a vendor with no valid TIN who you pay $900 across the year is below the reporting threshold, while one you pay $2,400 crosses it and the withholding obligation attaches.
The trap is the word cumulative. It is not $2,000 per invoice, it is $2,000 across the calendar year to that vendor. A contractor you pay $500 four times has crossed the line, and if you never collected their W-9 you were supposed to be withholding by the time the fourth payment went out. This is exactly why the practical control is to collect the W-9 from every vendor at onboarding rather than trying to decide, invoice by invoice, whether this is the payment that crosses the threshold.
How do I stop backup withholding once it starts?
You stop withholding once the underlying problem is fixed. If the vendor sends a properly completed W-9 with a valid TIN, you stop withholding on payments made after you receive it. If the IRS sent you a CP2100 notice, you send the vendor a B notice, and once they return a corrected W-9 (or, for a second B notice, proof from the IRS or the Social Security Administration), withholding stops.
What you cannot do is refund the tax you already withheld and deposited. That money is with the IRS. It gets reported in Box 4 of the vendor's 1099 and they claim it as a credit when they file. Vendors sometimes push hard for a refund from you directly; the answer is that the money is no longer yours to give back.
Who is exempt from backup withholding?
Most corporations are exempt from 1099 reporting for ordinary services, and payments that are not reportable are not subject to backup withholding either. The W-9 has an exempt payee code field where a corporation, tax-exempt organization, or other exempt entity states its status. Note the well-known exceptions that still get a 1099 even when the vendor is a corporation: payments to attorneys, and medical and healthcare payments. Do not assume an incorporated law firm is outside the rules.
Foreign vendors sit outside this system entirely. They give you a W-8 series form, not a W-9, and different withholding rules apply. If a vendor with a foreign address hands you a W-9, that is worth a second look before you pay them.
What happens if you fail to backup withhold?
The liability lands on the payer. If you were required to withhold and did not, the IRS can hold your business responsible for the amount you should have withheld, plus penalties and interest. You cannot go back to the vendor and claw it out of a payment you already made in full. On top of that, filing a 1099 with a missing or incorrect TIN carries its own per-form penalty, and those add up quickly across a vendor file.
This is the argument for treating the W-9 as a hard gate rather than a nice-to-have. A vendor record without a valid, matched TIN should not be payable at all. If that gate lives in your AP system rather than in someone's memory, it holds even when a purchase is urgent and someone senior is asking why the payment has not gone out.
How AP teams keep backup withholding at zero
The teams that never deal with this treat vendor onboarding as a compliance checkpoint. Before a vendor is marked payable, they have a signed W-9, the TIN has been run through the IRS TIN matching service, the legal name matches the TIN, and the payment details are verified. Nothing about that is complicated. It fails in practice because the request gets made by email, the form comes back as a scanned attachment, and it sits in an inbox until somebody remembers to file it.
Automating the intake fixes the leak. Vendors submit their tax and banking details through a portal instead of emailing a PDF, the TIN is validated at the point of entry, and the vendor is not payable until the record is complete. When forms do arrive as attachments, you can pull the details straight out of those emails instead of retyping them, which removes the transcription errors that cause a name and TIN mismatch in the first place. If you want the wider picture of how these forms fit together, our guides to W-9 vs 1099 and 1099 reporting in accounts payable cover the reporting side.
The payoff is not just avoiding a 24% withholding calculation. It is that January stops being a month of chasing vendors for tax details on payments you made ten months ago. A clean vendor master, enforced by vendor onboarding software and fed by accounts payable automation, makes year-end reporting a report you run rather than a project you survive.
Frequently asked questions
What is backup withholding on a W-9?
The W-9 is where a vendor certifies they are not subject to backup withholding. Part II of the form asks them to confirm their TIN is correct and that the IRS has not notified them they are subject to withholding. If they cannot make that certification, or they never return the form, you withhold 24% of their reportable payments and send it to the IRS.
Is backup withholding bad?
It is not a penalty and it does not mean anyone did anything wrong, but it is money the vendor does not receive when they expect it, and it creates a filing obligation for you (Form 945). Vendors almost always prefer to fix their W-9. Payers almost always prefer never to trigger it.
How do I know if a vendor is subject to backup withholding?
Two ways. Either the vendor has not given you a valid TIN, which you can see from your own records, or the IRS has told you, through a CP2100 or CP2100A notice, that the name and TIN you reported do not match their records. Run TIN matching at onboarding and the first case disappears.
Does backup withholding apply to corporations?
Generally no, because payments to corporations for ordinary services are not 1099-reportable in the first place, and backup withholding follows reportability. The exceptions to watch are payments to attorneys and medical and healthcare payments, which are reportable even when the payee is a corporation.