IRS B-Notice Deadlines and Requirements: What You Must Do After a CP2100
B-Notice requirements aren't optional and they aren't flexible — they're IRS-defined deadlines with specific documentation requirements, and missing them converts a vendor data problem into a compliance failure that belongs entirely to your organization. When a CP2100 notice arrives, the clock starts immediately: 15 business days to send B-Notices, 30 days for vendors to respond, and backup withholding exposure if they don't. The organizations that handle B-Notices cleanly are the ones that already have the process built — outreach templates ready, tracking systems in place, and proof of mailing documented. The ones that scramble are the ones that find out about the deadline after it's already passed.
What a B-Notice Is and Why It's Required
A B-Notice is a formal written notice your organization is required to send to a vendor when the IRS reports that the name and TIN combination on a filed 1099 did not match IRS taxpayer records. It is triggered by a CP2100 or CP2100A notice — the IRS's formal notification that one or more information returns were filed with mismatched taxpayer data.
The B-Notice serves two purposes: it notifies the vendor of the mismatch, and it requires them to provide corrected taxpayer information. It also starts a documented compliance chain that the IRS can review if the mismatch recurs or if penalties are assessed.
- IRS issues CP2100 / CP2100A listing vendors with name/TIN mismatches
- Payer sends B-Notice to each affected vendor within 15 business days
- Vendor has 30 days to respond with corrected taxpayer information
- Payer revalidates corrected information via IRS TIN matching
- If vendor does not respond — backup withholding (24%) may apply
Failing to follow this process correctly — missing the deadline, sending the wrong notice type, or not documenting delivery — creates compliance exposure that belongs to the payer, regardless of whether the original mismatch was vendor-caused.
First B-Notice vs. Second B-Notice
The IRS distinguishes between two B-Notice types, and sending the wrong one is itself a compliance error.
| First B-Notice | Second B-Notice | |
|---|---|---|
| When it applies | First mismatch for this vendor within the IRS lookback period | Second mismatch for the same vendor within three calendar years |
| What it requests | A new signed Form W-9 | SSA verification (for SSN vendors) or IRS TIN confirmation letter (for EIN vendors) |
| W-9 sufficient? | Yes — a signed corrected W-9 satisfies the First B-Notice requirement | No — a W-9 alone is not sufficient for a Second B-Notice |
| Audit sensitivity | High | Very high — second mismatches indicate a systemic problem |
The distinction matters because a Second B-Notice requires the vendor to provide documentation directly from the SSA or IRS — not just a self-certified W-9. Sending a First B-Notice when a Second is required is a compliance error. Tracking mismatch history per vendor is what ensures the right notice type is sent.
Upload your CP2100 extract and the tool handles the workflow below automatically — classifying every payee as 1st or 2nd B-Notice, calculating your deadlines, flagging backup withholding triggers, and estimating your IRC §6721 penalty exposure based on your mismatch count and correction timing. Based on IRS Publications 1281 and 1586.
- 1st vs. 2nd B-Notice auto-classified
- Penalty exposure estimated
- Deadlines calculated automatically
- No account required
B-Notice Deadlines — What the IRS Requires
| Milestone | Deadline |
|---|---|
| B-Notice sent to vendor | Within 15 business days of CP2100 receipt, or by the date specified in the notice — whichever is later |
| Vendor response window | Generally 30 days from the date the B-Notice is received |
| Backup withholding begins | If vendor does not respond within the required window |
| Second B-Notice lookback | Three calendar years — a second mismatch within this window triggers Second B-Notice requirements |
The 15-business-day deadline is the one most frequently missed. Many organizations receive CP2100 notices through accounts payable departments that aren't tracking compliance deadlines — the notice sits unopened or unrouted until the window has already closed.
What a B-Notice Package Must Include
A compliant B-Notice package sent to a vendor should include:
- The IRS-provided B-Notice template appropriate to the notice type (First or Second)
- Clear identification of the mismatch: vendor name, TIN, and the form year involved
- A request for corrected taxpayer information
- For First B-Notices: instructions and a blank Form W-9 for the vendor to complete and return
- For Second B-Notices: instructions to obtain SSA or IRS documentation (not a W-9)
- An explanation of backup withholding and what triggers it
- A clear response deadline
- Your organization's contact information for questions
After the B-Notice: What Happens Next
If the Vendor Responds
When a vendor provides corrected taxpayer information in response to a First B-Notice:
- Store the signed corrected W-9 securely and link it to the vendor record
- Resubmit the corrected name + TIN for IRS TIN matching — do not assume the correction is right
- If the revalidation confirms a match, update the vendor master and document the resolution
- If the revalidation still fails, restart the outreach process with the specific failure detail
If the Vendor Does Not Respond
If the vendor does not provide corrected taxpayer information within the response window:
- Begin backup withholding at the current IRS rate (24%) on future payments
- Document the date withholding began and the reason
- Continue withholding until the vendor provides valid taxpayer information and a match is confirmed
- Remit withheld amounts to the IRS and retain remittance records
- Document all outreach attempts — this record supports compliance if the vendor later disputes withholding
Backup Withholding: When It Applies and What It Requires
Backup withholding at 24% applies when a vendor fails to provide valid taxpayer information in response to a B-Notice, when a vendor refuses to provide a TIN, or when a vendor's TIN cannot be validated after reasonable outreach.
Withholding documentation should include:
- The date withholding began and the triggering reason
- The vendor's non-response status and outreach history
- Amounts withheld per payment period
- IRS remittance records
- The date withholding ended (when a valid TIN is finally confirmed)
Backup withholding disputes are one of the most significant operational consequences of poor B-Notice management. They affect vendor relationships, payment processing workflows, and require IRS remittance coordination — all of which could have been avoided with validated vendor data at onboarding.
What to Track for Every B-Notice
| Field | What to Record |
|---|---|
| CP2100 receipt date | Day the notice arrived — starts the 15-business-day clock |
| Vendor name and TIN | As reported in the CP2100 |
| Mismatch type | Name, TIN, both, or TIN type |
| B-Notice type | First or Second |
| Date B-Notice sent | Must be within 15 business days |
| Proof of delivery | Certified mail receipt, delivery confirmation |
| Vendor response date | Date corrected W-9 or SSA documentation received |
| Revalidation result | Match / still mismatched |
| Backup withholding status | Start date, end date, amounts withheld |
| Resolution date | Date vendor record updated and confirmed filing-ready |
B-Notice Timeline — How It Flows
| Day | Action |
|---|---|
| Day 0 | CP2100 notice received; receipt date logged; compliance owner assigned |
| Days 1–15 | B-Notices prepared, sent, and documented; proof of mailing retained |
| Days 16–45 | Vendor response window; reminders sent for non-responsive vendors |
| Day 45+ | Backup withholding begins for non-responding vendors |
| Upon response | Corrected W-9 or SSA documentation received; revalidation run |
| After confirmed match | Vendor record updated; withholding stopped; resolution documented |
Common B-Notice Mistakes
| Mistake | Why It's a Problem |
|---|---|
| Missing the 15-business-day deadline | Mandatory IRS requirement — late delivery is a compliance failure |
| Sending First B-Notice when Second is required | Wrong notice type doesn't satisfy IRS requirements |
| No proof of mailing retained | Can't demonstrate delivery if vendor claims non-receipt |
| Accepting a W-9 for a Second B-Notice | W-9 alone is insufficient — SSA or IRS documentation required |
| Not revalidating after receiving corrected W-9 | Correction may still fail — must be confirmed via TIN matching |
| Not starting backup withholding after non-response | Withholding obligation exists regardless of vendor cooperation |
| No mismatch history tracked per vendor | Can't determine First vs. Second without prior mismatch records |
Best Practices
- CP2100 notices routed immediately to a designated compliance owner on receipt
- Receipt date logged the day the notice arrives — clock starts immediately
- Mismatch history tracked per vendor to determine First vs. Second notice type
- B-Notices sent within 15 business days — no exceptions
- Proof of mailing retained for every notice sent
- Reminder outreach sent to non-responding vendors at Day 15 and Day 30
- Second B-Notice documentation requirements enforced — W-9 alone not accepted
- Corrected W-9s revalidated via IRS TIN matching before vendor is cleared
- Backup withholding started promptly for non-responding vendors and documented
- All outreach, responses, revalidations, and withholding records retained per vendor
B-Notice Compliance Checklist
- CP2100 notice receipt date logged immediately on arrival
- Compliance owner assigned; 15-business-day deadline tracked
- Each vendor reviewed: First vs. Second B-Notice determined from mismatch history
- B-Notice package prepared with correct IRS template and response instructions
- B-Notice sent within 15 business days of CP2100 receipt
- Proof of mailing or delivery confirmation retained per vendor
- Reminder outreach sent for non-responding vendors at Day 15 and Day 30
- Corrected W-9 received and stored securely (First B-Notice)
- SSA or IRS documentation received and verified (Second B-Notice)
- Corrected information revalidated via IRS TIN matching before vendor is cleared
- Backup withholding started, documented, and remitted for non-responding vendors
- Full B-Notice record retained: mismatch, notice type, outreach, response, revalidation, resolution
Frequently Asked Questions
What triggers a B-Notice requirement?
B-Notices are triggered when the IRS issues a CP2100 or CP2100A notice listing vendors whose name and TIN combinations did not match IRS records on filed information returns.
How long do I have to send a B-Notice after receiving a CP2100?
Generally within 15 business days of receiving the CP2100 notice, or by the date specified in the notice — whichever is later. This is a firm deadline.
What is the difference between a First and Second B-Notice?
A First B-Notice is sent for an initial mismatch and requires the vendor to provide a new signed W-9. A Second B-Notice is sent when the same vendor is mismatched again within three calendar years and requires SSA verification (for SSN vendors) or an IRS TIN confirmation letter (for EIN vendors) — a W-9 alone is not sufficient.
What if the vendor ignores the B-Notice?
If the vendor does not respond with corrected taxpayer information within the response window, backup withholding (24%) may apply on future payments. Document all outreach attempts and the date withholding begins.
Can validating vendors at onboarding reduce B-Notice workload?
Significantly. B-Notices are a downstream consequence of mismatches that reached a 1099 filing. IRS TIN matching at onboarding and Q4 bulk revalidation catch those mismatches before filing — so most of them never appear on a CP2100 in the first place.
Conclusion
B-Notice compliance is deadline-driven, documentation-dependent, and directly connected to how well your organization manages vendor data before and after filing. The 15-business-day deadline is firm. The First vs. Second distinction has real consequences. Backup withholding applies whether or not the vendor cooperates. And proof of delivery is not optional. Organizations that build a consistent B-Notice process — with clear routing, tracked deadlines, correct notice types, documented delivery, and revalidated corrections — convert a high-stress compliance event into a manageable workflow. Organizations that don't find out the hard way that every missed step has a cost attached.
Reduce B-Notice Workload with TIN Comply
CP2100 B-Notice Triage Tool
Upload your CP2100 extract or paste the data directly. The tool classifies every payee as 1st or 2nd B-Notice, calculates your send deadline and backup withholding start date, estimates your IRC §6721 penalty exposure by correction tier, and exports a prioritized action list — all based on IRS Publications 1281 and 1586.
- Classifies every payee as 1st or 2nd B-Notice automatically
- Estimates IRC §6721 penalty exposure by correction tier
- Calculates 15-business-day send deadline and BWH start date
- Detects 2-in-3 year rule — flags payees where no action needed
- Exports prioritized action list as CSV
- No account required — runs entirely in your browser