Form 3520 Mailing Address: Where to File and How to Get It Right

Form 3520 and Form 3520-A are forms that a person or entity may be required to submit under IRS requirements. If a required form is not submitted on time and there is no extension, a CP15 notice will be issued if the IRS catches the problem. The CP15 notice is what triggers the penalty assessment. Not every late filing results in a CP15 notice or a penalty.

Mailing Form 3520 correctly is a small administrative step with serious consequences. The right address, complete attachments, and reliable proof of mailing can keep an otherwise accurate filing from being treated as late or not filed.

Where to Mail Form 3520 — and Why It's Filed Separately

The form 3520 mailing address listed in the Instructions for Form 3520, Rev. December 2025, is:

Internal Revenue Service Center P.O. Box 409101 Ogden, UT 84409

Form 3520 is filed separately from your income tax return — don't attach it to your Form 1040. The IRS LB&I practice unit confirms it goes to the Ogden Campus, apart from the return itself.

Before mailing, review the current IRS Instructions for Form 3520, especially the "When and Where To File" section. If your filing involves a foreign trust, the background in our guide to foreign trusts and large foreign gifts may help.

What Belongs on the Envelope or Cover Letter

The instructions give the address but don't prescribe envelope or cover-letter wording. In practice, many use a plain envelope addressed exactly as printed, identifying the contents simply as "Form 3520."

A short cover letter may identify the taxpayer's name and taxpayer identification number, the tax year, whether the submission is original, amended, or delinquent, and the enclosed documents.

Don't rely on a cover letter to fix an incomplete form. The instructions state that only a complete Form 3520 is considered timely filed, and it is complete only when all required attachments are included.

Common Mistakes That Make a Good Filing Look "Not Filed"

• Sending it to the wrong IRS service center;
• Filing it together with, rather than separately from, the income tax return;
• Omitting required schedules, statements, or a substitute Form 3520-A where applicable;
• Missing a required signature or date; and
• Failing to keep evidence that it was mailed.

The stakes are real. If the IRS catches a required Form 3520 that was submitted late, incomplete, or incorrect and there was no extension, it may issue a CP15 notice that triggers the penalty assessment. Under section 6677, the penalty may be — generally the greater of $10,000 or a percentage of the gross amount involved: 35% for certain trust transfers or distributions, 5% for certain Form 3520-A-related failures, and, under section 6039F, 5% per month up to 25% for an unreported foreign gift. Reasonable cause, properly demonstrated, may prevent a penalty — our Form 3520 and 3520-A penalty overview explains this exposure in depth.

When to File Form 3520 and How to Prove Timely Mailing

Generally, Form 3520 is due on the 15th day of the fourth month after your tax year ends — for calendar-year individuals, generally the same day as the income tax return due date. It moves to the 15th day of the sixth month if you're a U.S. citizen or resident living and working outside the United States and Puerto Rico (or in military or naval service outside those areas), with the required statement attached. An extension can push it to the 15th day of the tenth month. If the due date falls on a Saturday, Sunday, or legal holiday, file by the next business day.

Many practitioners send it by certified mail with return receipt. Keep the dated mailing receipt, tracking history, return receipt, a complete copy of the signed filing, and every attachment. The postmark can matter as evidence of when the package entered the mail, though the instructions don't spell out a Form 3520-specific postmark rule.

What to Do If It Went to the Wrong Address

Act quickly: confirm the correct address, prepare a complete replacement package, and mail it by a trackable service. Keep the original mailing evidence, returned envelope, tracking history, and a short written explanation of what happened.

If the IRS has already issued a CP15 notice, don't assume resending the form resolves the matter. Check the notice deadline and consider professional help — our penalty appeal and abatement guide covers what comes next, and the IRS's IRM 20.1.9 discusses penalty administration for incomplete international information returns.

Is Electronic Filing Available?

Electronic filing availability can change, and the current Form 3520 sources don't establish an e-filing procedure. Before relying on electronic submission, check with the IRS or a qualified professional about current options. If e-filing isn't available or isn't right for you, use the Ogden address and keep dated proof of submission.

If a mailing error has led the IRS to issue a CP15 notice, counsel can review your filing history, correspondence, and reasonable-cause facts under attorney-client privilege once an engagement letter is signed. At the Law Offices of Jason R. Kovan, Jason Kovan — an international tax attorney and CPA with 27+ years of international tax experience — provides counsel-led representation focused on Form 3520, Form 3520-A, and CP15 matters. We welcome a confidential conversation about your situation.

Private, personalized guidance, with attorney-client privilege applying once an engagement letter is signed.

Contact the Law Offices of Jason R. Kovan