When Is Form 706 Due? Federal Estate Tax Return Deadline and Extensions

The attorney mentioned Form 706. The CPA mentioned Form 706. And now you are staring at a calendar trying to figure out when this thing is actually due --- and whether you even need to file it at all.

For most American families in 2026, the answer is that Form 706 is not required. But the deadline matters if it is, because missing it triggers penalties and interest that compound quickly on large estates.

The Standard Deadline: 9 Months After Death

IRS Form 706, the United States Estate (and Generation-Skipping Transfer) Tax Return, is due nine months after the date of death.

If a person died on March 15, 2026, the Form 706 is due by December 15, 2026. If the due date falls on a weekend or federal holiday, it shifts to the next business day.

This is a hard calendar deadline, not tied to the tax year. It does not follow the April 15 schedule that applies to income tax returns.

The 6-Month Extension

If you need more time, you can request an automatic six-month extension by filing IRS Form 4768 (Application for Extension of Time to File a Return and/or Pay U.S. Estate Taxes) before the original nine-month deadline.

This extends the filing deadline to fifteen months after the date of death. For the March 15 death example, the extended deadline would be June 15, 2027.

Two critical points about the extension:

The extension is for filing, not for paying. If estate tax is owed, the estimated tax must still be paid by the original nine-month deadline. The extension gives you more time to prepare the return, but interest accrues on any unpaid tax from the original due date.

You do not need to explain why. The six-month extension is automatic when Form 4768 is filed on time. The IRS does not require a reason.

When You Must File Form 706

Form 706 is required only when the gross estate plus adjusted taxable gifts exceeds the federal estate tax exemption. For 2026, that threshold is $15,000,000 per individual under the One Big Beautiful Bill Act (OBBBA).

If the total is below $15 million, no Form 706 is required and no federal estate tax is owed.

The gross estate includes real property, bank accounts, investments, retirement accounts, life insurance proceeds (where the decedent owned the policy), business interests, and the decedent's share of jointly held property. It also includes the value of lifetime taxable gifts --- gifts above the annual exclusion ($19,000 per recipient in 2026) made during the decedent's life.

When You Might File Even at Zero Tax: Portability

There is one important reason to file Form 706 voluntarily when no tax is owed: electing portability.

Portability allows a surviving spouse to claim the deceased spouse's unused estate tax exemption (the DSUE amount). If the deceased spouse's estate used $3 million of their $15 million exemption, the remaining $12 million can transfer to the surviving spouse --- but only if Form 706 is filed and the portability election is made.

Without filing, the unused exemption disappears permanently.

For families where the surviving spouse's own assets might grow over time through investment returns, an inheritance from their own parents, or life insurance proceeds, the portability election can shelter up to the full $30 million from federal estate tax on the survivor's later death. The cost of preparing the return is often worth it for that insurance.

State Estate Tax Returns

Filing a federal Form 706 can trigger state-level filing requirements even in states with no active estate tax. In New Mexico, for example, if a federal Form 706 is filed for any reason --- including purely to elect portability --- the executor must also file New Mexico Form RPD-41058 with a copy of the federal 706 attached. The state tax is zero, but filing it yields a Certificate of No Tax Due, which functions as a lien release that title companies and banks require before clearing property transfers.

Other states have their own estate tax returns with different thresholds. Massachusetts and Oregon, for instance, impose state estate tax on estates over $1 million --- far below the federal threshold. If the decedent owned property in multiple states, check each state's requirements independently.

What Happens If You Miss the Deadline

If Form 706 is required and you miss the nine-month deadline without an extension:

• Failure-to-file penalty: 5% of the unpaid tax per month, up to 25%
• Failure-to-pay penalty: 0.5% of the unpaid tax per month, up to 25%
• Interest: accrues from the original due date at the IRS underpayment rate

These penalties apply only to unpaid tax. If the estate owes nothing --- because it falls below the $15 million threshold --- there is no penalty for a late filing.

For the portability election, there is a simplified late filing procedure (Revenue Procedure 2022-32) that allows eligible estates to file a late Form 706 solely for portability within a specified window. Consult a CPA if you missed the deadline but want to elect portability.

If you are handling the full estate settlement in New Mexico --- the final income tax return, the fiduciary income tax, the probate decision, and the RPD-41058 --- the New Mexico Final Tax & Estate Tax Guide puts every form, deadline, and filing requirement into a single chronological roadmap.

See more New Mexico guides →