By Alexey Spasskiy · Published March 16, 2026 · Updated September 18, 2026 · 9 min read
The IRS SS-4 fax number for domestic (U.S.-based) applicants is 855-641-6935. You can fax your completed Form SS-4 — the Application for Employer Identification Number — to that number 24/7 and receive your EIN back by fax within 4 business days.
If you need an EIN fast and aren't eligible to apply online, faxing is the next-best option. It's far quicker than mailing (which takes 4–5 weeks) and doesn't require a physical fax machine — you can send Form SS-4 from your phone using mFax.to in under two minutes.
This guide covers every IRS SS-4 fax number, who uses which one, and the exact steps to fax your application correctly.
IRS SS-4 Fax Numbers at a Glance
| Applicant Type | Fax Number | Hours |
|---|---|---|
| Domestic (U.S. 50 states & D.C.) | 855-641-6935 | 24/7 |
| International — calling from within the U.S. | 855-215-1627 | 24/7 |
| International — calling from outside the U.S. | 304-707-9471 | 24/7 |
Fax destination address
All SS-4 fax applications are processed by the IRS EIN Operation in Cincinnati, OH 45999. You do not need to write this on the form — the fax number routes it automatically.
What Is Form SS-4 and Who Needs It?
Form SS-4 is the IRS application for an Employer Identification Number (EIN) — a nine-digit federal tax ID used to identify a business entity. You need an EIN if you are:
- Starting a new business (LLC, corporation, partnership, or sole proprietorship)
- Hiring employees for the first time
- Opening a business bank account
- Filing business taxes
- Administering an estate or trust
- Applying for business credit
Once issued, your EIN is permanent and tied to your business for its lifetime. The IRS does not charge a fee to apply.
Online is faster — if you qualify
The IRS online EIN application is available Monday–Friday, 7 a.m.–10 p.m. Eastern and issues your EIN immediately. If you are eligible, apply online at IRS.gov first. Faxing is the right choice when the online system is unavailable, you are a foreign applicant, or you need to apply outside of those hours.
EIN Application Methods: Speed Comparison
| Method | Processing Time | Available To |
|---|---|---|
| Online (IRS.gov) | Immediately | U.S. entities with SSN/ITIN, Mon–Fri 7am–10pm ET |
| Fax (Form SS-4) | 4 business days | All applicants, 24/7 |
| Phone | Same day | International applicants only (267-941-1099) |
| 4–5 weeks | All applicants |
Faxing beats mail by weeks and is the only 24/7 option for most applicants. If you're incorporating over a weekend or need an EIN before Monday morning's bank appointment, faxing Form SS-4 is your best bet.
Fax is the right choice when:
- The online application is closed (it runs Monday–Friday, 7 a.m.–10 p.m. Eastern) or not working
- You're an international applicant, or your responsible party has no U.S. taxpayer ID
- Your responsible party already got an EIN online today — the IRS issues only one EIN per responsible party per day online
- You want a paper record of exactly what you submitted: the fax confirmation page plus your copy of the SS-4
Key Fields to Complete on Form SS-4
Incomplete or inconsistent forms are the most common reason an EIN is delayed. These are the lines that matter most — and where applicants most often go wrong:
| Line | Field | What to Enter |
|---|---|---|
| 1 | Legal name | Exactly as registered with your state, punctuation and "LLC" or "Inc." included |
| 2 | Trade name | Your DBA, only if it differs from the legal name |
| 4a–4b | Mailing address | Where the IRS will mail your CP 575 confirmation letter |
| 7a–7b | Responsible party + SSN/ITIN/EIN | A real individual who controls the entity — not the LLC or corporation itself, and not a nominee. Foreign applicants without an SSN or ITIN write foreign or N/A on 7b |
| 8a–8c | LLC details | Number of members and tax classification — often left blank by mistake |
| 9a | Entity type | Sole proprietorships, LLCs and S corporations are the ones most often confused |
| 10 | Reason for applying | Pick the reason that fits — "Started new business" isn't always right |
| 11 | Business start date | MM/DD/YYYY |
| 13 | Expected employees | The highest headcount you expect in the next 12 months |
| 16–17 | Business activity | Be specific — "services" or "consulting" invites a manual review |
The responsible party named on Line 7a must also sign the form. Government entities are the only applicants that may list something other than an individual there.
How to Fax Form SS-4 to the IRS
Download the current Form SS-4
Get the latest version of Form SS-4 directly from IRS.gov (currently Rev. December 2025). Do not use an outdated version — the IRS may reject it. Download, complete, and save the PDF before sending.
Complete every required field
Fill in your legal entity name (exactly as it appears on state formation documents), entity type, responsible party name and SSN or ITIN, business address, and reason for applying. Leave no applicable field blank — incomplete applications are returned without an EIN.
Prepare a fax cover sheet
Add a brief cover sheet that includes your name, return fax number, phone number, and the note "SS-4 Application for EIN." The IRS may call you directly if they have questions — an incorrect phone number means delays. See our IRS fax cover sheet guide for a ready-to-use template.
Send to the correct IRS SS-4 fax number
Domestic applicants: 855-641-6935. International applicants within the U.S.: 855-215-1627. Outside the U.S.: 304-707-9471. Using the wrong number is one of the most common mistakes — double-check before sending.
Save your transmission confirmation
Keep the delivery confirmation from your fax service as proof of submission. Do NOT resend the form if you're unsure it went through — duplicate applications for the same entity are denied. Wait at least 5 business days before following up.
Watch for your EIN by fax
The IRS faxes your EIN back within 4 business days. A formal CP 575 confirmation letter follows by mail in 2–3 weeks to your Form SS-4 business address. If you haven't heard back in 5 business days, call the IRS Business & Specialty Tax Line at 800-829-4933.
The return fax number is the step people miss
The IRS faxes your EIN to the return fax number on your cover sheet. Leave it off and the IRS mails the EIN instead — the 4–5 week route you were trying to avoid. If you send with mFax and have your own mFax fax number, give that as the return number and the IRS fax lands in the app.
What to Put on the Cover Sheet
- To: Internal Revenue Service, EIN Operation
- Fax: 855-641-6935, or the international number that applies to you
- From: your full legal business name
- Return fax number: where the IRS should fax your EIN — mandatory
- Phone number: so the IRS can call if something on the form is unclear
- Date and page count: total pages including the cover sheet, with every page numbered in order
- Note: "Enclosed: Form SS-4, EIN application. Please fax the EIN to the number above."
Faxing Form SS-4 Without an SSN or ITIN
Foreign nationals and non-resident applicants who do not have — and are not eligible for — a Social Security Number or Individual Taxpayer Identification Number can still obtain an EIN by fax.
On Line 7b of Form SS-4, enter foreign or N/A in place of an SSN or ITIN. Fax the completed form to the international line:
- Within the U.S.: 855-215-1627
- Outside the U.S.: 304-707-9471
Mail your application to: Internal Revenue Service, Attn: EIN International Operation, Cincinnati, OH 45999
International applicants: phone may be faster
International applicants can also call 267-941-1099 (Monday–Friday, 6 a.m.–11 p.m. Eastern) to receive an EIN the same day. If you need the number immediately, the phone option is quicker than fax.
Common Mistakes When Faxing Form SS-4
Avoid these errors to prevent your application from being delayed or rejected:
1. Using an outdated form version. The IRS rejects old SS-4 versions. Always download from IRS.gov and check the revision date (bottom left of the form).
2. Entity name mismatch. The name on your SS-4 must match your state registration documents exactly — even a spelling difference can cause rejection.
3. Wrong fax number. Domestic applicants must use 855-641-6935. Using an expired or incorrect number means your form goes nowhere.
4. Submitting multiple applications. If you're unsure your fax went through, wait — don't resend. The IRS denies EINs for duplicate applications.
5. Missing signature. Form SS-4 requires a signature from the responsible party. An unsigned form will not be processed.
6. Including extra documents. Send only the completed SS-4 and a cover sheet. Attached articles of organization, operating agreements, or identification documents slow processing.
7. No return fax number on the cover sheet. The IRS falls back to mailing your EIN, which adds weeks.
8. The wrong responsible party. Line 7a must name the individual who actually controls the entity — not the LLC or corporation itself, and not a nominee. A wrong name misdirects every future IRS notice.
9. The wrong entity type. Line 9a trips up LLCs most often — check how your LLC is taxed before you tick a box.
10. A vague business description. "Services" or "consulting" on Line 17 invites a manual review. Name the actual product or service.
11. Applying before the entity exists. Register the business with your state first — the IRS recommends forming the entity before you apply for its EIN.
What Happens After You Fax Form SS-4
Once the IRS receives your faxed SS-4, processing follows a predictable timeline:
| Timeframe | What Happens |
|---|---|
| Days 1–4 | IRS processes application under the Fax-TIN program |
| ~Day 4 | EIN returned by fax to the number you provided |
| 2–3 weeks | CP 575 confirmation letter arrives at your business address |
| 60 days | Deadline to report responsible party changes using Form 8822-B |
Your EIN will be in the format XX-XXXXXXX (two digits, hyphen, seven digits). Once you have it, you can use it immediately — no waiting for the letter.
Keep the CP 575 letter permanently — it is your official proof of EIN assignment and hard to replace. If the IRS finds a problem on your form, it contacts you by phone at the number on your cover sheet, or by letter; fix the issue it names and resubmit.
Before you e-file or pay electronically
Wait about 2 weeks after receiving your EIN before using it to e-file a return or make electronic tax deposits — the number needs time to activate across IRS systems. If a return is due before you have the EIN at all, write "Applied For" and the application date in the EIN field. Never use your SSN in its place.
What If Your EIN Doesn't Arrive?
If 5 business days pass with no fax from the IRS, work through this in order:
- Check your fax confirmation — the right number was dialed and the transmission shows as successful
- Check your return fax number — it must be active and able to receive faxes
- Call the IRS Business & Specialty Tax Line at 800-829-4933 — Monday–Friday, 7 a.m.–7 p.m. local time, with your SS-4 details and confirmation page to hand
- Allow for backlogs — around tax season and fiscal year-ends, fax processing can run past 4 business days
- Don't re-fax unless the IRS confirms it never received the original — a second submission creates a duplicate record
If the delay is causing genuine financial hardship, the Taxpayer Advocate Service at 877-777-4778 can escalate your case.
Fax Form SS-4 From Your Phone with mFax.to
You don't need a physical fax machine to send Form SS-4 to the IRS. mFax.to lets you upload your completed PDF, enter the fax number (855-641-6935), and send — straight from your iPhone or Android phone.
- No fax machine, no UPS store, no waiting in line
- Secure encrypted transmission for sensitive tax documents
- Delivery confirmation so you have proof of submission
- Available 24/7 — fax at midnight before your Monday morning bank appointment
Over 5 million users trust mFax.to for time-sensitive documents. For more on faxing IRS forms securely, see our guide to faxing IRS forms and the full IRS fax numbers reference. Faxing another IRS form next? See how to fax Form 2553 for an S corporation election and Form 4506-C.
Frequently Asked Questions
What is the IRS SS-4 fax number for domestic applicants?
The IRS SS-4 fax number for U.S.-based applicants is 855-641-6935, available 24 hours a day, 7 days a week.
How long does it take to get an EIN by fax?
The IRS processes faxed Form SS-4 applications within 4 business days and sends your EIN back by fax. A written CP 575 letter arrives by mail within 2–3 weeks.
Can I fax Form SS-4 without an SSN or ITIN?
Yes. Enter foreign or N/A on Line 7b and fax to 855-215-1627 (within the U.S.) or 304-707-9471 (outside the U.S.).
What happens if I fax SS-4 to the wrong number?
Your application will not reach the IRS. Wait a reasonable period and re-fax to the correct number. Check your transmission confirmation — if the fax didn't connect, you are safe to resend.
Is it safe to fax sensitive tax information?
It is, provided you use a secure fax service. mFax.to transmits documents with end-to-end encryption, ensuring your SSN and business details are protected in transit. Learn more about secure IRS faxing.
Send your Form SS-4 now — download the form from IRS.gov, complete it, and fax to 855-641-6935 using mFax.to. No fax machine needed, and you'll have your EIN in 4 business days.