What is Form SS-4 for?
The 1-page IRS application that assigns an Employer Identification Number to a business entity. Eighteen numbered lines, 1 signature. Filed online (15 minutes), fax (4 business days), mail (4 weeks), or attached to a phone call for foreign entities. Cost is $0.
Every EIN assigned since 1936 traces back to an SS-4 filing. The current revision is dated December 2019 and is published at irs.gov/pub/irs-pdf/fss4.pdf. Every field on the current SS-4 maps to a specific IRS Master File record entry.
Which SS-4 line triggers which rejection code?
Every rejection code maps to a specific line. Line 1 → code 101. Line 7b → 102 or 106. Line 8/9a → 108. Line 17 → 103. Line 18 → 104. Codes 109-113 are technical (server-side). Code 114 is the 24-hour cap. Code 115 catches deceased responsible parties.
| Line | Field | Code | Notes |
|---|---|---|---|
| 1 | Legal name of entity | 101 | Must match state formation cert character-for-character |
| 2 | Trade name (DBA) | 108 | Skip if identical to line 1; do not leave both blank |
| 3 | Executor/administrator/trustee name | 108 | Estate/trust only; blank triggers 108 in those categories |
| 4a-b | Mailing address, city, state, ZIP | 108 | Must be a real US address; PO Box permitted |
| 4c | County | 108 | County for state on line 4b, not state of formation |
| 5a-b | Street address of principal business | 108 | Physical location; can differ from mailing |
| 6 | County and state of principal business | 108 | Physical operations location |
| 7a | Responsible party name | 108 | Natural person only per IRS rule since May 2019 |
| 7b | Responsible party SSN or ITIN | 102 or 106 | Foreign RP writes "Foreign" here |
| 8a-c | LLC checkbox, # of members, organized in the US | 108 | LLC + 1 member = disregarded; 2+ = partnership |
| 9a | Type of entity | 108 | Records what the entity is; it is not the 8832 classification election |
| 9b | State of incorporation | 108 | US state or foreign country name |
| 10 | Reason for applying | 108 | 10 checkbox options: new business, hired employees, banking, etc. |
| 11 | Date business started | 108 | Formation date on state certificate |
| 12 | Closing month of accounting year | 108 | Calendar year default = December |
| 13 | Highest # of employees expected 12 months | 108 | 0 is a valid entry; drives Form 941 filing frequency |
| 14 | Form 944 annual-filing election | 108 | Check only if employment tax liability is $1,000 or less for the year |
| 15 | First date wages or annuities were paid | 108 | If no employees, mark N/A |
| 16 | Principal activity checkbox | 108 | One box only; drives the IRS business-activity code |
| 17 | Principal line of merchandise or service | 108 | Free-text description of what the entity actually sells |
| 18 | Has the entity ever applied for and received an EIN? | 103 | Yes triggers 103 if the prior EIN is still open |
| — | Third Party Designee block, then signature | 104 | Unnumbered, below line 18. Designee cap: 1 EIN per RP per day |
Which 4 lines cause most rejections?
Four lines carry every applicant-side rejection code. Line 1 fires 101, line 7b fires 102 or 106, line 8a-c fires 108, and line 9a fires 108. Every other line fires 108 only when left blank or filled with an invalid entry.
Read the full rejection playbook at reference number 101.
How does line 7b handle a foreign responsible party?
Write the word "Foreign" in line 7b. The IRS accepts this only on fax and mail submissions. The online Assistant blocks non-numeric entries within 2 seconds via code 106. Foreign RPs fax to 855-215-1627. Response is 4 business days at $0.
Read the SSN-optional workflow at EIN without an SSN.
Does line 9a lock your tax classification for 60 months?
No. Line 9a asks what the entity is, so the IRS opens the right account and expects the right return. It is not an election, and checking a box there does not start a 60-month clock.
The 60-month limit is real, but it lives elsewhere. Under 26 CFR § 301.7701-3(c)(1)(iv), an eligible entity that elects to CHANGE its classification on Form 8832 cannot elect again for 60 months after the effective date. The same paragraph carves out the case most new filers are in: an initial election by a newly formed entity, effective on its date of formation, is not subject to that limit at all.
What line 9a does control is whether the application clears. A wrong entry triggers code 108 at submission, and correcting it means a fresh SS-4 or, once the EIN exists, Form 8832. Read the full application walkthrough at how to apply for an EIN and the code-101 recovery path at EIN reference number 101.
Which SS-4 submission channel wins?
Fax wins on the speed-per-rejection tradeoff. Online is fastest at 15 minutes but blocks foreign responsible parties under code 106. Mail is slowest at 4 weeks. Phone serves foreign entities only. Fax delivers in 4 business days across every applicant type, at $0 in IRS fees.
| Channel | Where to send | Response time | Codes fired |
|---|---|---|---|
| Online (irs.gov/EIN) | irs.gov EIN Assistant, Mon-Fri 7 a.m.-10 p.m. ET | 15 minutes if no rejection | Fires 7 codes in real time |
| Fax (US) | Fax 855-641-6935 | 4 business days | 0 online-only codes fire |
| Fax (foreign) | Fax 855-215-1627 | 4 business days | Accepts line 7b = Foreign |
| Mail (Cincinnati) | IRS Center, Cincinnati OH 45999 | 4 weeks | 0 real-time rejection possible |
| Phone (foreign only) | 267-941-1099, Mon-Fri 6 a.m.-11 p.m. ET | 45-minute call | Live IRS operator assigns EIN |
Fax beats mail by 8-16x on elapsed time and dodges every online-only rejection code (101, 102, 106, 109-114). Mail to Internal Revenue Service Center, Attn: EIN Operation, Cincinnati OH 45999 — all 50 states, US territories and foreign applicants use that one address.
What happens after you submit the SS-4?
Nine stages run between submission and a confirmed EIN on the IRS Master File. Rejection codes fire at stages 2, 4 and 5, all inside the first 24 hours. The CP-575 confirmation letter mails 4-6 weeks after assignment, so the paper trail closes that long again after a mailed SS-4 delivers the number in 4 weeks.
| Stage | Timing | What the IRS does |
|---|---|---|
| 1. Submission receipt | Same day (online) or 1-3 days (fax) | IRS logs the SS-4 into the assignment queue |
| 2. Field validation | Within 24 hours | IRS checks the SS-4 fields for missing/invalid entries (codes 106, 108) |
| 3. Name-control hash computation | Within 24 hours | IRS computes the 4-character name control from the line 1 legal name |
| 4. Master File comparison | Within 24 hours | IRS checks the name control against existing EIN records (code 101 fires here) |
| 5. Responsible-party validation | Within 24 hours | IRS validates the line 7b TIN against SSA records (codes 102, 106, 115) |
| 6. EIN assignment | Same session (online), 4 days (fax), 4 weeks (mail) | IRS assigns the EIN and records the campus prefix |
| 7. Master File write | Within 48 hours of assignment | IRS records EIN, legal name, name control, entity type, responsible party, address |
| 8. CP-575 mailing | 4-6 weeks after assignment | IRS prints and mails the CP-575 confirmation letter |
| 9. Downstream TIN-matching failure | After the first 1099 filing season | A payer that files a 1099 under a mismatched name/EIN pair receives CP-2100 or CP-2100A and must send that payee a B-notice |
Stage 9 is the one that surfaces late. A name control that does not match the EIN stays invisible until a payer files a 1099 against it: the IRS then sends that payer a CP-2100 or CP-2100A listing the mismatched payee, and the payer issues a B-notice. Fix the pairing before it reaches that point at IRS name control, and read the confirmation letter itself at CP-575.