By David Thompson · Published March 16, 2026 · Updated June 8, 2026 · 7 min read
Quick Answer: Fax number porting transfers your existing fax number to a new provider so you keep the same number while upgrading your service. The process takes 7–15 business days and requires a Letter of Authorization (LOA) plus a recent bill. mFax Business supports number porting with all plans.
Switching fax providers shouldn't mean losing the number your clients, partners, and vendors already have on file. Fax number porting lets you move your existing number from one carrier to another — whether you're going from a landline fax machine to an online fax service, or switching between cloud fax providers.
This guide covers exactly how porting works, what it costs, how long it takes, and the mistakes that delay transfers.
Your Right to Port
The FCC's Local Number Portability (LNP) rules guarantee your right to keep your phone or fax number when switching providers. Your current carrier cannot refuse a valid porting request or charge a fee to release the number.
What Is Fax Number Porting?
Fax number porting is the process of transferring an existing fax number from one service provider to another. Instead of getting a new number when you switch, you keep the one your contacts already know.
The term comes from Local Number Portability (LNP), a set of FCC regulations that allow consumers and businesses to retain their telephone numbers when changing carriers. Since fax numbers are technically telephone numbers, the same rules apply.
Porting works for:
- Landline fax numbers — moving from a physical fax machine to an online service
- VoIP fax numbers — switching between internet-based fax providers
- Toll-free fax numbers — transferring 800, 888, 877, and similar numbers
- Virtual fax numbers — moving a virtual fax number between cloud providers
Why Port Your Fax Number?
There are several reasons businesses choose to port rather than get a new number:
- Client continuity — your customers, partners, and vendors already have your fax number. Changing it means updating business cards, letterheads, websites, government filings, and insurance forms.
- Regulatory compliance — healthcare providers, law firms, and financial institutions often have fax numbers registered with regulatory bodies. Changing them triggers paperwork.
- Brand consistency — a long-standing fax number signals stability and professionalism.
- Zero downtime — porting transfers the number seamlessly. You receive a temporary number during the transition, so you never miss a fax.
Bottom Line
If your fax number appears on business cards, contracts, or government forms — port it. The process is worth the small effort to avoid the chaos of updating every reference.
How to Port Your Fax Number (Step-by-Step)
The porting process follows the same general steps regardless of which provider you're moving to.
Gather Your Information
Before contacting your new provider, collect these details from your current carrier:
- Account number — found on your bill or by calling your carrier
- Account holder name — must match exactly (including middle initials, LLC suffixes, etc.)
- Service address — the address on file with your current carrier
- Authorized contact — the person authorized to make changes on the account
- A recent bill — a copy from the last 30 days showing the fax number and account details
If you're unsure about any of these, call your current provider and ask for a Customer Service Record (CSR). This document lists everything you need.
Sign Up with Your New Provider
Create an account with your new fax service. You'll typically receive a temporary fax number immediately so you can start sending and receiving faxes right away while the port completes.
When choosing a new provider, check that they support number porting — most do, but the process and fees vary. See our comparison of the best online fax services for a breakdown.
Submit a Letter of Authorization (LOA)
Your new provider will give you a Letter of Authorization (LOA) form. This is the legal document that authorizes the transfer.
Fill it out carefully — even small mismatches cause rejections:
- The name must match your current carrier's records exactly
- The address must match character-for-character
- The fax number must include the area code
- Sign and date the form (electronic signatures are usually accepted)
Submit the completed LOA along with your recent bill to your new provider's porting team.
Wait for the Transfer
Your new provider submits the port request to your current carrier. The current carrier verifies the information and either approves or rejects it.
During this time:
- Do NOT cancel your old service — canceling before the port completes can release your number permanently
- Keep paying your old provider until the transfer is confirmed
- Use the temporary number your new provider gave you for outgoing faxes
- Incoming faxes to your old number continue arriving at your old provider until the port completes
Verify and Go Live
Once the port is approved, your fax number switches to your new provider — usually overnight. You'll receive a notification from your new provider confirming the transfer.
After confirmation:
- Send a test fax to verify the number is working (see our guide to sending a test fax)
- Cancel your old service (now that the port is complete, canceling is safe)
- Update any fax cover sheets or templates with your new provider's details
Never Cancel First
The most common porting mistake is canceling your old service before the transfer completes. If the number is disconnected, it may be released back to the number pool — and you lose it permanently. Wait for written confirmation from your new provider before canceling.
How Long Does Fax Number Porting Take?
Porting timelines depend on the type of number and the carriers involved.
| Port Type | Typical Timeline |
|---|---|
| Local fax number (landline to online) | 7–15 business days |
| VoIP to VoIP (cloud to cloud) | 5–10 business days |
| Toll-free number (800, 888, 877) | 10–20 business days |
| Complex port (multiple numbers, different carriers) | 4–6 weeks |
| International number | Varies widely — contact provider |
Most standard single-number ports complete within two weeks. Delays usually come from information mismatches on the LOA, not from the actual transfer process.
How Much Does Fax Number Porting Cost?
Porting costs fall into two categories: what your new provider charges to bring the number in, and what your old provider charges (spoiler: they can't charge a release fee under FCC rules).
| Cost Type | Typical Range |
|---|---|
| Port-in fee (new provider) | $0–$25 one-time |
| Port-out fee (old provider) | $0 (FCC prohibits blocking) |
| Monthly service (new provider) | Depends on plan |
| Temporary number | Usually included free |
Some providers include porting free with their plans, while others charge a one-time setup fee of $15–$25. mFax Business includes number porting with all business plans starting at about $9/mo (billed annually) — and because plans are usage-based, you build your own by choosing the exact seats and pages you need rather than paying for a rigid fixed tier.
FCC Protection
Your current provider cannot charge you a fee to release your number or refuse a valid port request. If they give you pushback, reference FCC Rule 47 CFR § 52.34 — your right to port is protected by federal law.
Common Porting Problems (and How to Avoid Them)
Most porting delays come from preventable mistakes. Here are the top issues and how to dodge them:
1. Name mismatch on the LOA The name on your Letter of Authorization must match your carrier's records exactly. "John Smith" vs. "John A. Smith" or "Smith LLC" vs. "Smith, LLC" will trigger a rejection. Request a Customer Service Record from your carrier to confirm the exact name on file.
2. Wrong service address Your address must match character-for-character — including apartment numbers, suite designations, and abbreviations. "St." vs. "Street" matters.
3. Canceling before the port completes If you disconnect your old service before the number transfers, the number may be released back to the carrier's pool. Always wait for written confirmation from your new provider.
4. Outstanding balance on old account Some carriers will delay porting if your account has an unpaid balance. Clear any outstanding invoices before submitting the port request.
5. Number is on a bundled plan If your fax number is part of a bundled phone/internet plan, porting it out may require unbundling first. Contact your old provider to separate the fax line before submitting the LOA.
Porting vs. Getting a New Number
Not sure if porting is worth it? Here's when each option makes sense:
| Scenario | Best Option |
|---|---|
| Your fax number is on business cards, contracts, and regulatory filings | Port it |
| You're a new business setting up fax for the first time | New number |
| Your current number has been receiving spam or junk faxes | New number |
| Clients and vendors regularly fax you at this number | Port it |
| You want to be up and running in minutes, not weeks | New number (for now) |
| You're switching from a physical fax machine to cloud fax | Port it |
If you need a virtual fax number immediately, most providers — including mFax — assign one instantly when you sign up. You can always port your old number in later and either keep both or replace the temporary one.
How to Choose a Provider That Supports Porting
When evaluating fax services for a port, check for these features:
- Free or low-cost porting — avoid providers that charge more than $25
- Temporary number — you need to fax during the transition
- Porting support team — a dedicated team speeds up the process
- Number portability check — some providers let you verify portability before signing up
- No long-term contract — flexibility to switch again if needed
For a detailed comparison, see our guide to the best online fax services or learn how to choose the best fax app for your business.
Get Started
Porting your fax number is straightforward: gather your account details, sign an LOA, and let your new provider handle the rest. The entire process takes about two weeks — a small wait to keep the number your contacts already know.
For personal faxing, download the mFax app — upload a document and send in under 2 minutes.
For business teams, mFax Business gives you number porting, virtual fax numbers, and a shared dashboard — and you build your own plan to fit your team with a live calculator, starting at about $9/mo.