Portability of the Estate Tax Exclusion: The Election, the Deadline, and the Late Fix

When a married person dies without using all of the federal transfer tax exclusion, the unused portion can be carried over to the surviving spouse. That carried-over amount is the deceased spousal unused exclusion, and it exists because of a provision in Internal Revenue Code section 2010(c).

It does not happen by itself. The executor of the first estate has to file a federal estate tax return and make the election on it. If no return is filed, the exclusion is simply gone, and the family often does not learn this until the second death, when the number would have mattered.

The election is the whole mechanism

Form 706 is the federal estate tax return. Most estates never file one, because the gross estate falls below the filing threshold. Portability inverts that instinct: to preserve the first spouse's unused exclusion, the executor must file the return specifically to make the election, even where the estate owes nothing and would otherwise have no federal filing obligation at all.

The election is made by filing a complete and properly prepared return. There is no separate election form and no box that must be checked to opt in. An executor who wants to decline portability has to say so affirmatively on the return. That default cuts in the family's favor, but only for an estate that files.

Two features of the amount are frequently misunderstood. The carried-over exclusion is a fixed dollar figure determined at the first death — it does not grow with inflation the way the survivor's own exclusion does. And it applies only to the estate and gift tax. The generation-skipping transfer exemption is a separate allowance that does not port; if the first spouse's GST exemption is not allocated, it disappears.

Verify before relying: exclusion amounts, filing thresholds, and the inflation adjustments that move them change by statute and annually by revenue procedure. Legislation enacted in 2025 replaced the reduction that had been scheduled for 2026 with a new base amount that is indexed going forward. Take the current figures from the IRS estate tax page, never from memory or from an older article.

The clock, and the route back when it is missed

1. Date of death

   The nine-month period for filing Form 706 begins. Nothing about portability starts later, and the executor's authority to make the election attaches at once.

2. Within nine months

   File the return, or file for the automatic extension of time to file. An extension of time to file is not an extension of time to pay, but for a portability-only estate there is normally nothing to pay.

3. Nine months plus the extension

   The last day for a timely election. A complete return filed by this date secures the carried-over exclusion permanently, subject to the IRS's ability to re-examine the amount later.

4. After the deadline, for estates not otherwise required to file

   A revenue procedure issued in 2022 provides a simplified method with a window running to the fifth anniversary of death. It replaced an earlier procedure that allowed only two years. The return must state at the top that it is filed under the revenue procedure.

5. After the simplified window, or for estates above the threshold

   The only remaining route is a request for an extension of time to make a regulatory election through a private letter ruling. That is slow, costs a user fee, and is not guaranteed.

Deadline discipline: the simplified procedure is available only to estates that were not required to file for any other reason. An estate that crossed the filing threshold and simply did not file has no access to it, and the private ruling route is materially harder. Determine which category the estate is in before doing anything else.

What a portability-only return actually contains

A return filed solely to elect portability is a real return, not a placeholder. The IRS can examine the first estate's return to determine the correct carried-over amount at any time the survivor's estate or gift tax position depends on it — including long after the ordinary assessment period for the first estate has closed. A thin return is therefore a deferred problem, not a saved fee.

• A complete inventory of the gross estate, with each asset identified and valued.
• Appraisals for real property, closely held business interests, and other assets without a public market.
• Deductions claimed, including the marital and charitable deductions that reduce the taxable estate to zero in most portability filings.
• Prior taxable gifts and the exclusion already used against them, since the carried-over amount is a residual.
• Any generation-skipping transfer exemption allocation, which must be made on this return because it will not port.
• The executor's signature, plus documentation of authority to act where no formal appointment exists.

Regulations recognize that some valuations on a portability-only return do not change the tax and permit an estimate-based approach for property passing to a surviving spouse or to charity, provided the return identifies the property and the estate exercises due diligence. That relief does not extend to assets whose value affects the exclusion computation, and it does not excuse an unsupported inventory. Where the executor is also a beneficiary, the duty of loyalty makes the decision to skip a return a fiduciary question as well as a tax one — the survivor benefits, the remainder beneficiaries may not.

Portability compared with a credit shelter trust

There is no general answer. Families with modest estates and appreciated homes often do better with portability and the basis adjustment; families with fast-growing assets, blended-family concerns, generation-skipping goals, or exposure to a state estate tax often do better with a funded trust. Many plans do both, using a disclaimer or a clayton-style election so the decision can be made after the first death, when the numbers are actual rather than projected.

Questions the desk gets

The first spouse died several years ago and no return was filed. Is it too late?

Possibly not. If that estate was not otherwise required to file, the simplified procedure allows a late election into the fifth year after death. Confirm the date of death, confirm the estate was under the threshold in the year of death, and file promptly with the required statement on the return. Past the window, the remaining option is a private letter ruling request, which is slower and not assured.

Does the surviving spouse have to be a U.S. citizen?

Not for the election itself, but a non-citizen surviving spouse changes the surrounding analysis substantially, because the unlimited marital deduction generally requires a qualified domestic trust. That is a separate structure with its own funding, trustee, and distribution rules. Treat a non-citizen survivor as a specialist question rather than an adjustment to a standard plan.

Can the surviving spouse use the carried-over amount for lifetime gifts?

Yes. The carried-over exclusion is generally applied before the survivor's own exclusion when taxable gifts are made, which is useful because it locks in the amount before a later remarriage could displace it. Gifts still have to be reported on a gift tax return in the year made, and the election's paperwork trail has to be preserved to support the amount claimed.

Does a state estate tax follow the federal election?

Usually not. States with their own estate tax set their own exclusion, their own filing deadline, and their own rules on whether anything transfers to a survivor. A small number provide a portability-style election; most do not, and several use a much lower threshold than the federal one. Check the decedent's state and any state where real property sits, as labelled examples rather than as a general rule.

What to do next

Within the first month after a death, answer three questions in writing: what the gross estate is, whether the estate is required to file for any reason other than portability, and whether the surviving spouse's projected estate could ever exceed the exclusion. If the answer to the third is anything other than a confident no, file the return. The cost of an unnecessary portability filing is a professional fee; the cost of a missed one is measured against a tax rate.

The same return is where generation-skipping allocations are made, so coordinate it with any trust planning already in place — see our briefs on grantor trusts and income tax and irrevocable life insurance trusts. The administration duties surrounding the filing are covered in fiduciary duties of executors and trustees, and further material sits on the Estate, Tax & Succession desk. This brief is general information about federal transfer tax rules that Congress and Treasury change often; it is not tax or legal advice for any estate.