How to Extend Form 3520

How a Form 3520 extension works

Form 3520 is due on the 15th day of the 4th month after the end of the filer’s tax year: April 15 for a calendar-year individual. Under the Form 3520 instructions, if the filer is granted an extension of time to file their income tax return, Form 3520 is due no later than the 15th day of the 10th month, October 15.

Weekend and legal holiday dates move to the next business day. The Form 3520 & 3520-A due dates by year table lists the adjusted dates and the COVID-era postponements for earlier years.

Extending with Form 4868

1. File Form 4868 by April 15. E-file it or mail it. Paying some or all of the estimated tax electronically and marking the payment as an extension also counts as filing Form 4868. See IRS Form 4868.
2. The extension covers Form 3520 automatically. There is no separate Form 3520 application, and Form 3520 isn’t listed on Form 4868.
3. Check line 1k on Form 3520 and enter the number of the return that was extended. For a Form 4868, enter “1040”.
4. Mail Form 3520 by October 15 to the Ogden address, separately from the Form 1040 and with proof of mailing. See where to mail Form 3520 and what goes in the envelope. Form 3520 is filed on paper; see can Form 3520 be e-filed?

Form 4868 extends the time to file, not the time to pay income tax. Form 3520 itself reports no tax, but the client’s Form 1040 balance is still due April 15.

Filers living abroad: June 15

A U.S. citizen or resident gets an automatic two months, to June 15, if on the regular due date they either:

• live outside the United States and Puerto Rico, with their place of business or post of duty outside the United States and Puerto Rico; or
• are in military or naval service on duty outside the United States and Puerto Rico.

No form is needed for the June 15 date. Check line 1j on Form 3520 and attach a statement showing the filer qualifies. To go further, file Form 4868 by June 15 (checking its “out of the country” box) for October 15.

The October 15 limit. Some filers abroad extend their Form 1040 past October 15, for example with Form 2350 or a request for additional time. Form 3520 doesn’t follow. The instructions set Form 3520’s extended due date at no later than the 15th day of the 10th month, and note that it isn’t tied to the income tax return’s due date. Calendar Form 3520 for October 15 even when the Form 1040 is due later.

Estates, decedents, and entities

• A U.S. decedent’s final-year Form 3520 is due April 15 after the decedent’s last tax year. It moves to October 15 if the decedent’s income tax return is extended.
• A U.S. decedent’s estate files by the 15th day of the 4th month after the estate’s tax year ends. An extension of the estate’s income tax return moves it to the 15th day of the 10th month.
• Partnerships, corporations, and trusts filing Form 3520 use the same 15th-day-of-the-4th-month rule. An extension of their own income tax return extends Form 3520, but no later than the 15th day of the 10th month.

Form 3520-A is extended separately

If the client owns a foreign grantor trust, there may be a second return on an earlier clock. The trust’s Form 3520-A is due the 15th day of the 3rd month after the trust’s year ends: March 15 for a calendar-year trust. It is extended only by Form 7004 with form code 27, filed under the trust’s EIN by March 15, to September 15. A Form 4868 does not extend it.

A substitute Form 3520-A, which the U.S. owner prepares when the trustee won’t file, is different: it is attached to the owner’s Form 3520 and is due with it, including the Form 4868 extension. Read Form 3520-A is due March 15: extending it with Form 7004.

If the deadline has passed

A Form 4868 filed after April 15 (or June 15 for filers abroad) doesn’t extend Form 3520. A late Form 3520 can carry penalties under IRC § 6039F for foreign gifts and § 6677 for foreign trusts. Penalty relief depends on the facts. Start with late Form 3520: streamlined versus delinquent procedures and the reasonable cause guide.

Frequently asked questions

Is there a separate extension form for Form 3520?

No. Form 3520 is extended by extending the filer’s income tax return. For an individual, a timely Form 4868 moves Form 3520 to October 15. Check line 1k on Form 3520 and enter “1040”.

Does Form 4868 extend Form 3520-A?

No. Form 3520-A is the foreign trust’s return and is extended only by Form 7004 with form code 27, filed under the trust’s EIN by the 15th day of the 3rd month after the trust’s year ends. A substitute Form 3520-A attached to the owner’s Form 3520 does follow the Form 3520 due date, including the Form 4868 extension.

Can Form 3520 be extended past October 15?

No. The Form 3520 instructions set the extended due date at no later than the 15th day of the 10th month after the end of the filer’s tax year, even if the income tax return is extended further.

Sources and filing references

This article uses the December 2025 Instructions for Form 3520 and Form 3520-A. Check the current IRS instructions before filing.

• IRS Instructions for Form 3520
• IRS Instructions for Form 3520-A · Local instructions PDF
• IRS Form 4868 · IRS Form 7004
• IRC § 6039F · IRC § 6677