How to fax the IRS from your phone

Updated October 31, 2026

There is no single IRS fax number. The right number depends on your notice or form, so use the one printed on your letter or listed on the IRS page for it.

Fax Once is not affiliated with the IRS. This is general information, not tax advice.

Find the right number

Look at your letter first. Many notices give a fax number. The notice number is usually in the top or bottom right corner, such as CP120A.
Look up the notice on IRS.gov. Search for "Understanding your" and the notice number. The page says what to send and where. Some notices use different numbers for different answers, and CP120A is one example.
For a form, read its instructions. Form SS-4 and Form 4506-T list their own fax numbers, and 4506-T's number depends on your state.

Don't use a number from an old letter or another website without checking it. A number meant for one notice may not reach the team handling yours.

Can I use an app or online fax service?

The IRS says so on its notice pages. Its CP120A page says to fax "using either a fax machine or online fax service." It also tells you to protect yourself "by understanding the fax service's privacy and security policies." Our privacy page lists what we receive, who handles it and how long it is kept.

What to include

A copy of the notice's first page, if the notice asks for it.
Your name and taxpayer number on every page, as the notice directs.
Every page the notice asks for, in order.
A cover sheet with the page count, if you want one.

Keep your proof

Save the delivery receipt with your tax records, along with a copy of what you sent. Fax Once deletes pages from your iPhone once the fax is delivered and keeps only the receipt, so save your own copy first. Read what a fax confirmation does and doesn't show.

Before you send

Tax papers hold sensitive details, and fax is not encrypted from end to end. If your notice gives another option, such as an IRS online account or mail, compare it first. Also make sure the letter is really from the IRS. If you aren't sure, check the notice number on IRS.gov and use the number listed there.

Sources: IRS, Understanding your CP120A notice; IRS, Instructions for Form SS-4; IRS, where to file Form 4506-T.