By David Thompson · Published March 18, 2026 · Updated March 18, 2026 · 8 min read
The SS-4 form fax number for domestic U.S. applicants is 855-641-6935. Fax your completed Form SS-4 — the IRS application for an Employer Identification Number — to that number any time, day or night, and expect your EIN back by fax within 4 business days.
Faxing is the fastest option available 24/7 for most applicants. If the IRS online EIN tool is unavailable or you are applying outside business hours, faxing Form SS-4 beats mailing by several weeks. And you don't need a physical fax machine — mFax.to lets you upload the PDF and send it from your phone in under two minutes.
SS-4 Form Fax Numbers at a Glance
The correct fax number depends on where your business is located — not on your entity type or which state you're in.
| Applicant | SS-4 Fax Number | Available |
|---|---|---|
| U.S. domestic (all 50 states + D.C.) | 855-641-6935 | 24/7 |
| International — faxing from within the U.S. | 855-215-1627 | 24/7 |
| International — faxing from outside the U.S. | 304-707-9471 | 24/7 |
All three numbers connect to the IRS Fax-TIN program. Applications are processed at the IRS EIN Operation in Cincinnati, OH.
One number for all entity types
LLCs, corporations, sole proprietors, partnerships, trusts, nonprofits, and government entities all use the same fax number — 855-641-6935 — as long as the business has a U.S. address. There is no state-by-state or entity-type breakdown.
What Is Form SS-4?
Form SS-4 is the IRS application for an Employer Identification Number (EIN) — a nine-digit federal tax ID in the format XX-XXXXXXX. An EIN functions as your business's equivalent of a Social Security Number for tax purposes.
You need an EIN to:
- Open a business bank account
- Hire employees and run payroll
- File federal business tax returns
- Apply for business licenses or credit
- Form an LLC, corporation, or partnership
- Administer an estate or trust
The IRS issues EINs at no charge. You will use it for the life of your business — an EIN is permanent and does not expire.
Which SS-4 Fax Number Should You Use?
The routing is simple: domestic or international.
Use 855-641-6935 if:
- Your business has an address in any U.S. state, Washington D.C., or a U.S. territory such as Puerto Rico or Guam
- You are an individual (sole proprietor) with a U.S. mailing address
Use 855-215-1627 if:
- Your business is located outside the U.S. but you are faxing from a U.S. phone line or internet fax service
Use 304-707-9471 if:
- You are physically outside the United States and faxing from an international phone line
Sending to the wrong number
If you fax to the wrong number, your SS-4 will not reach the IRS. Double-check which number applies before you send. If your fax was confirmed delivered but you receive no response, call the IRS Business & Specialty Tax Line at 800-829-4933 to verify receipt.
How to Fill Out Form SS-4 Before Faxing
Incomplete applications are the most common reason for delays. Complete every applicable line before you send.
| Line | Field | What to Enter |
|---|---|---|
| 1 | Legal name | Exact name as registered with your state — match it character for character |
| 2 | Trade name | DBA name, if different from legal name |
| 4a–4b | Mailing address | Where the IRS will mail your CP 575 letter |
| 7a | Responsible party name | A real individual (not another business entity), with legal authority over the entity |
| 7b | Responsible party SSN/ITIN | Required; foreign applicants who don't have one may write "foreign" or "N/A" |
| 8a | LLC members | Number of members, if applying for an LLC |
| 9a | Entity type | LLC, corporation, partnership, sole proprietor, trust, estate, etc. |
| 10 | Reason for applying | Started new business, hired employees, banking purposes, estate, compliance requirement, etc. |
| 11 | Business start date | MM/DD/YYYY format |
| 13 | Expected employees | Highest headcount expected in the next 12 months |
| 16–17 | Business activity | General category and specific product or service |
Always download the current form version from IRS.gov. The bottom-left of the form shows the revision date — as of early 2026, the current version is Rev. December 2025. Outdated versions may be rejected.
How to Fax Form SS-4: Step-by-Step
Download and complete the current Form SS-4
Get Form SS-4 directly from IRS.gov (search "Form SS-4" or go to irs.gov/forms-pubs). Fill in every applicable line using the field guide above. Use black ink if printing by hand, or complete the fillable PDF digitally for cleaner results. Save the completed PDF before proceeding.
Prepare a fax cover sheet with your return fax number
This step is non-negotiable. Include a cover sheet listing your name, business name, a callback phone number, and — most critically — your return fax number. The IRS will fax your EIN to that number. Without it, they mail the EIN instead, adding 3–4 weeks. See our IRS fax cover sheet guide for a ready-to-use template.
Send to the correct SS-4 fax number
Domestic applicants: fax to 855-641-6935. Open mFax.to on your phone or computer, upload the completed PDF, enter the fax number, and send. The IRS Fax-TIN line accepts faxes 24/7 — you can submit at any hour.
Save your fax confirmation
Keep the delivery confirmation from your fax service. This is your proof of submission. If you used mFax.to, you receive a timestamped delivery receipt automatically. Do not submit again unless you have confirmed the fax failed — duplicate applications for the same entity are denied.
Wait up to 4 business days for your EIN
The IRS will fax your EIN to the return number on your cover sheet within 4 business days of receipt. If you haven't heard back after 5 business days, call the IRS Business & Specialty Tax Line at 800-829-4933 (Monday–Friday, 7 a.m.–7 p.m. local time) to check the status.
The return fax number is the most common missed step
When we tested the SS-4 fax process, the return fax number field is the single most-missed requirement. If the IRS can't fax your EIN back to you, they revert to mail — a process that takes 4–5 weeks. Include your return fax number on the cover sheet and verify it is correct before sending.
What Happens After You Fax Form SS-4
Once the IRS receives a complete and accurate SS-4 by fax, processing follows a predictable timeline:
| Timeframe | What Happens |
|---|---|
| Days 1–4 | IRS processes application under the Fax-TIN program |
| ~Day 4 | EIN faxed back to the return number on your cover sheet |
| 2–3 weeks | CP 575 confirmation letter mailed to your Form SS-4 address |
| 60 days after assignment | Deadline to report responsible party changes via Form 8822-B |
Your EIN is active as soon as the IRS issues it — you don't need to wait for the CP 575 letter. Keep that letter permanently; it is your official proof of EIN assignment and is difficult to replace.
If you need to use your EIN before it arrives — for example, a tax return is due — you may write "Applied For" and the application date in the EIN field of that return.
SS-4 Application Methods Compared
| Method | Processing Time | Who Can Use | EIN Delivery |
|---|---|---|---|
| Online (IRS.gov) | Immediate | U.S. entities, SSN/ITIN required, Mon–Fri 6am–1am ET | On-screen, download instantly |
| Fax (SS-4) | ~4 business days | All applicants, 24/7 | IRS faxes back to your return number |
| Phone | Same day during call | International applicants only | Verbal; note it down immediately |
| 4–5 weeks | All applicants | EIN mailed to form address |
Online is the fastest route if you qualify. The restriction: you must have a U.S. business address and a responsible party with a Social Security Number, ITIN, or existing EIN. One EIN may be issued online per responsible party per day.
Faxing is the right choice when:
- The online tool is down or outside business hours
- You are an international or foreign applicant
- Your responsible party does not have a U.S. taxpayer ID
- You want a 24/7 submission option with faster turnaround than mail
For more detail on all four methods, see our complete guide to faxing IRS forms.
Faxing SS-4 Without an SSN or ITIN
Foreign nationals and non-resident applicants who are not eligible for a Social Security Number or ITIN may still obtain an EIN by fax.
On Line 7b of Form SS-4, write foreign or N/A in place of a taxpayer ID. Then fax to the international line:
- Faxing from within the U.S.: 855-215-1627
- Faxing from outside the U.S.: 304-707-9471
Alternatively, international applicants can call 267-941-1099 (Monday–Friday, 6 a.m.–11 p.m. Eastern) to receive an EIN the same day by phone — faster than fax for this specific group.
Foreign applicants: mail address
If mailing instead of faxing, foreign applicants send Form SS-4 to: Internal Revenue Service, Attn: EIN International Operation, Cincinnati, OH 45999.
6 Mistakes That Delay Your SS-4 EIN
1. No return fax number on the cover sheet. The IRS defaults to mailing your EIN, adding 4+ weeks. Always include a return fax number.
2. Using an outdated form version. Download the current SS-4 from IRS.gov and check the revision date in the bottom-left corner.
3. Entity name mismatch. The name on your SS-4 must match your state formation documents exactly. Even a missing comma or "LLC" can trigger rejection.
4. Wrong fax number. Domestic applicants must use 855-641-6935. Using any other number — including old or third-party-listed numbers — means your form goes nowhere.
5. Submitting by multiple methods simultaneously. Do not fax and mail at the same time. Duplicate applications for the same entity are denied. Pick one method and wait.
6. Listing a nominee as the responsible party. The IRS requires the actual controlling person — a real individual, not a placeholder. Incorrect responsible party information misdirects all future IRS notices.
Fax Form SS-4 From Your Phone — No Fax Machine Needed
You don't need a fax machine, a landline, or a trip to a copy shop to fax your SS-4. mFax.to lets you:
- Upload your completed SS-4 PDF directly from your phone or computer
- Enter the IRS fax number (855-641-6935) and send
- Receive a timestamped delivery confirmation as proof of submission
- Get your EIN faxed back to the same mFax number — no hardware required
Over 5 million users rely on mFax.to for sensitive document submissions. For encrypted fax transmission of tax documents, it's both faster and more secure than driving to a UPS Store. See our full guide to faxing Form SS-4 to the IRS for additional context on the process.
Frequently Asked Questions
What is the SS-4 form fax number?
The SS-4 form fax number for all U.S.-based applicants is 855-641-6935, available 24 hours a day, 7 days a week under the IRS Fax-TIN program.
How long does it take to get an EIN after faxing Form SS-4?
Approximately 4 business days for a complete, accurate application. Errors, missing fields, or IRS backlogs can extend processing to several weeks. If you don't hear back in 5 business days, call 800-829-4933.
Do I need to put a return fax number on the SS-4 form?
Yes. Without a return fax number, the IRS will mail your EIN instead of faxing it — a process that takes 4–5 weeks. Include your return fax number on your cover sheet before sending.
Can I fax SS-4 and apply online at the same time?
No. Submit by one method only. Duplicate applications for the same entity are rejected. If you apply online successfully, your EIN is issued immediately — no need to also fax.
What is the IRS phone number to check my SS-4 fax status?
Call the IRS Business & Specialty Tax Line at 800-829-4933, Monday–Friday, 7 a.m.–7 p.m. local time. Have your SS-4 information and fax confirmation page ready when you call.
Ready to send? Download Form SS-4 from IRS.gov, complete every field, add a cover sheet with your return fax number, and fax to 855-641-6935 using mFax.to. No fax machine. No store visit. EIN in 4 business days.