Estate Tax Portability Election & DSUE: The Complete 2026 Guide

When a spouse dies, their unused federal estate tax exemption can transfer to the surviving spouse — but only if the executor files the right form within a strict deadline. Miss it and the IRS keeps up to $15,000,000 of sheltering power. Here's exactly how portability works, what the DSUE is worth, and when a credit shelter trust is still the better call.

What is portability? The DSUE explained

Under IRC §2010(c), the surviving spouse may use the Deceased Spouse's Unused Exclusion (DSUE) — the portion of the deceased spouse's federal estate and gift tax exemption that was not consumed by their taxable estate. The surviving spouse stacks the DSUE on top of their own exemption.

The DSUE is calculated at the moment of the first spouse's death:

DSUE = Applicable exemption at death − Taxable estate of deceased spouse

Three scenarios that illustrate the math

2026 exemption $15,000,000 per IRS 2026 inflation adjustments (OBBBA). DSUE = $15M minus deceased's taxable estate (minimum $0). Survivor retains their own $15M plus the DSUE.

The filing requirement — and why it trips people up

Portability is not automatic. To capture the DSUE, the executor must file Form 706 (United States Estate Tax Return) — even if the estate owes zero estate tax and is well under the $15M filing threshold.²

Deadlines:

• Standard deadline: 9 months from date of death
• Automatic extension: additional 6 months by filing Form 4768 on or before the 9-month deadline → total of 15 months to file

Missed the deadline? Rev. Proc. 2022-32 gives you five years

If the 15-month window has closed but the estate was not required to file Form 706 (i.e., the estate was below the applicable filing threshold at the time of death), Revenue Procedure 2022-32 provides a simplified late-election procedure:³

1. File a complete, properly-prepared Form 706
2. Write at the top: "FILED PURSUANT TO REV. PROC. 2022-32 TO ELECT PORTABILITY UNDER § 2010(c)(5)(A)"
3. File on or before the fifth anniversary of the decedent's date of death

No private letter ruling needed. No IRS permission required. As long as the filing is timely and complete, relief is automatic.

Four important DSUE limitations

1. The DSUE is not indexed for inflation

The DSUE is locked at the amount calculated at the first spouse's death. It does not increase if the federal exemption rises later. Example: Spouse A dies in 2026 with a $3M estate — DSUE is $12,000,000. If Spouse B lives to 2030 when the exemption has inflated to $16M, their total shelter is $16M (own) + $12M (DSUE) = $28M — not $32M. The DSUE stays at $12M regardless of subsequent inflation adjustments.⁴

2. Only the most recently deceased spouse's DSUE counts

If Spouse B remarries after Spouse A's death, and Spouse B's new partner also predeceases them, the DSUE from Spouse A is wiped out. Only the DSUE of the last deceased spouse is available at the surviving spouse's death.⁴ This matters significantly in second-marriage situations — work with counsel before remarriage if there is a substantial DSUE to protect.

3. The GST exemption is NOT portable

Portability applies only to the estate and gift tax exemption under IRC §2010. The generation-skipping transfer (GST) tax exemption under IRC §2631 is not portable. A deceased spouse's unused GST exemption cannot transfer to the surviving spouse. Each individual must use their own GST exemption or lose it.

This is one of the most important reasons credit shelter trusts remain valuable even after OBBBA. By funding a credit shelter trust at the first spouse's death — and allocating GST exemption to it — families can shelter trust assets from estate tax at every generation's death without relying on portability. See: Dynasty Trust Guide for how GST exemption allocation works across generations.

4. Portability does not exist for most state estate taxes

Nearly all states with their own estate tax — including New York, Massachusetts, Washington, Oregon, and Illinois — do not offer portability of their state exemption. Each spouse's state exemption is "use it or lose it" at death. This means a couple relying solely on federal portability may still face significant state estate tax when the survivor dies. See: State Estate Tax 2026 Guide.

Portability vs. credit shelter trust: which is right?

Post-OBBBA, with a permanent $15M exemption, many married couples with estates under $30M can rely entirely on portability. But for other families, the credit shelter trust (also called a bypass trust or B trust) remains essential. Here's how to think through the choice:

When portability alone is usually sufficient

• Combined estate under $30M, no state estate tax exposure (living in a non-estate-tax state)
• No dynasty/generation-skipping goals — children are beneficiaries, not grandchildren
• Assets are primarily financial accounts (not business interests with appreciation potential)
• No concern about second-marriage complications

When a credit shelter trust (or both) is the right call

• You live in a state with an estate tax — almost certainly need the trust to capture the state exemption at the first death
• You want GST protection — dynasty trust goals require allocating GST exemption at first death, which portability can't provide
• Rapidly appreciating assets (business, pre-IPO stock) — appreciation inside the bypass trust escapes the survivor's estate entirely
• Asset protection priority — trust assets are protected from the survivor's future creditors and a potential second spouse
• Estate exceeds $15M per spouse — some trust funding may be essential regardless

How portability interacts with prior gifts

Any taxable gifts made during the deceased spouse's lifetime reduce their available exemption at death, which reduces the DSUE. Example: if Spouse A gifted $5M to an IDGT during life (using $5M of exemption), and then died with a $3M estate, the calculation is: $15M exemption − $5M prior gifts − $3M estate = $7M DSUE. The prior gifts matter.

This is why lifetime gift planning and portability planning must be coordinated. A financial advisor modeling a large gifting strategy should simultaneously model the DSUE impact on the surviving spouse's long-term exposure. See: Annual Gift Calculator and Trust Strategies Guide.

DSUE and the irrevocable life insurance trust (ILIT)

Life insurance owned by the insured is included in their taxable estate. A common strategy is to have an Irrevocable Life Insurance Trust (ILIT) own a policy on the insured's life — this keeps the death benefit out of both spouses' estates.

If the first spouse to die owns a policy inside an ILIT, the death benefit goes to the ILIT (not the insured's taxable estate), so it doesn't reduce the DSUE. The ILIT-owned policy is already outside the estate by design. This means the surviving spouse's DSUE remains available, and the ILIT proceeds can be used to pay estate taxes on the survivor's estate or simply distributed to heirs tax-free.

Step-by-step: what to do when a spouse dies

1. Within 30 days: engage an estate attorney to assess whether the deceased's estate was under the $15M federal threshold. If it was, portability is likely available.
2. Within 60 days: determine whether a 706 needs to be filed for tax purposes. If not, decide whether to file solely for portability. In almost every case, if DSUE is available, file for it.
3. Before the 9-month deadline: have the estate attorney prepare and file Form 706. If more time is needed, file Form 4768 before the 9-month deadline to get the automatic 6-month extension.
4. When filing: the 706 must compute the DSUE amount. The executor elects portability simply by filing a complete and timely 706 — there is no separate election checkbox. The filing itself constitutes the election.
5. After filing: the surviving spouse keeps records of the DSUE. It will be used when they gift or die — the DSUE is applied first before the surviving spouse's own exemption, which matters for tracking purposes.
6. If missed: check Rev. Proc. 2022-32. If within 5 years of the decedent's death, file immediately with the required notation at the top.

Sources

1. IRS — Tax Year 2026 Inflation Adjustments (OBBBA) (federal estate and gift tax exemption $15,000,000 for 2026; OBBBA made permanent, signed July 4, 2025)
2. IRS — Frequently Asked Questions on Estate Taxes (Form 706 filing required to elect portability; 9-month deadline; Form 4768 extension; IRC §2010(c))
3. IRS Revenue Procedure 2022-32 (simplified late portability election: 5 years from date of death, for estates not required to file Form 706; supersedes Rev. Proc. 2017-34)
4. IRS Instructions for Form 706 (September 2025) (DSUE computation; portability election mechanics; IRC §2010(c)(4) DSUE lock-in at death; last deceased spouse rule under IRC §2010(c)(4)(B))
5. IRS — What's New in Estate and Gift Tax (GST exemption non-portability under IRC §2631; DSUE application order)

Values verified as of April 2026: federal estate/gift tax exemption $15,000,000 (OBBBA, IRS 2026 adjustments); Rev. Proc. 2022-32 5-year late-election window (IRS, July 2022); GST exemption non-portable under IRC §2631; DSUE locked at first death per IRC §2010(c)(4).