Portability Election: Surviving Spouse Tax Benefit

A married couple can shield $30 million from federal estate tax in 2026 — but the second spouse’s half of that shield vanishes unless someone files a tax return the estate is not otherwise required to file. The Deceased Spousal Unused Exclusion, or DSUE, is worth up to $6 million in avoided tax at the 40% federal rate, and it disappears by default. Not through a tax. Through inaction.

That is the mechanism this article quantifies: portability, the election that lets a surviving spouse add a deceased spouse’s unused federal estate tax exemption to their own. The figures below are confirmed against IRS Form 706 instructions, Congress.gov, and the Tax Foundation as of June 2026. One structural caveat shapes everything that follows: the One Big Beautiful Bill Act (P.L. 119-21), signed July 4, 2025, made the elevated exemption permanent at $15 million per individual. The “sunset cliff” that drove portability urgency for the better part of a decade no longer exists in current law. What replaced it is a quieter problem — and arguably a more expensive one, because the urgency that forced families to act is gone while the default loss remains.

The numbers that decide whether $6 million is preserved or lost

Five figures govern a portability decision. Each is verified against a primary source below.

Sources: IRS Instructions for Form 706 (Rev. September 2025); Congress.gov CRS Report R48183 (2026); Rev. Proc. 2022-32. Exemption amount set by One Big Beautiful Bill Act (P.L. 119-21).

Start with what portability actually transfers. When the first spouse dies and leaves an estate below the exemption, the unused portion — the DSUE — does not automatically pass to the survivor. federal estate tax exemption and rate data confirms the per-person figure at $15 million for 2026, which the Congressional Research Service (Report R48183, 2026) attributes to P.L. 119-21. Transfers between spouses are already exempt, so the first death rarely triggers tax. The exposure builds at the second death, when the survivor’s estate is measured against a single exemption unless the DSUE was captured.

How the election works, and what the calendar costs

Portability is not a checkbox on an existing return. It requires filing Form 706 — the United States Estate (and Generation-Skipping Transfer) Tax Return — for the first spouse’s estate, even when that estate owes nothing and would never be required to file otherwise. The IRS is explicit on this point: per the Instructions for Form 706 (Rev. September 2025), the election to allow the surviving spouse to use the decedent’s unused exclusion is made only by filing a timely and complete return, with Part 6 completed to compute the DSUE amount.

Timing is where families lose money. The statutory deadline is nine months after the date of death, extendable to fifteen months by filing Form 4768 before the original deadline lapses (IRS, Frequently Asked Questions on Estate Taxes, 2026). For estates below the filing threshold — which is most estates electing portability — the IRS built an escape hatch. Under Revenue Procedure 2022-32, an executor who was not otherwise required to file can make a late portability election up to the fifth anniversary of death, using a simplified return that estimates rather than precisely values marital- and charitable-deduction property. Miss even the five-year window and the only remaining path is a Private Letter Ruling, which the American College of Trust and Estate Counsel and practitioner commentary in Trusts & Estates describe as carrying a steep user fee plus attorney and accountant time. The election, once the deadline passes, becomes irrevocable.

One trap deserves naming because it is invisible until it isn’t: the “last deceased spouse” rule. A surviving spouse can only use the DSUE of their most recent deceased spouse. Remarry, and a new spouse who predeceases you wipes out the DSUE you were carrying from the first marriage. For a survivor sitting on several million dollars of ported exemption, remarriage without planning is a silent forfeiture event. This is the kind of mechanic that estate planning cost guide for $5M to $25M net worth treats as a core variable rather than a footnote.

Finluxy Estate Tax Exposure Index: portability’s dollar value across net worth tiers

The Finluxy Estate Tax Exposure Index estimates federal estate tax owed at the survivor’s death under two scenarios. Here the relevant comparison is not a tax-law sunset — that counterfactual is addressed separately below — but the practical fork every couple faces: portability elected versus portability lost. The Index assumes a married couple, all assets passing to the survivor at the first death, no lifetime gifting, and the survivor dying with the full combined estate under 2026 law. Tax is computed as (taxable estate − available exemption) × 40%.

Methodology: (taxable estate − available exemption) × 40%. Exemption figures per IRS and Congress.gov CRS R48183 (2026). Assumes no lifetime gifting and full asset transfer to survivor at first death. Illustrative; ignores state estate tax and post-death asset growth.

Read the bottom row. A couple worth $30 million who fails to elect portability hands the IRS $6 million that a single timely filing would have eliminated. The exposure is zero at $10 million because one exemption already covers the estate — which is precisely why so many executors skip the filing, and precisely the reasoning that destroys value when assets later appreciate past $15 million. A survivor at 60 with $12 million and thirty years of compounding ahead can easily cross the single-exemption line; the DSUE captured at the first death is what absorbs that growth. TCJA sunset risk and exemption changes walks through how legislative reversal would reshape these same tiers.

The counterfactual the Index was built to measure

Before OBBBA, the Exposure Index compared current law against a scheduled 2026 reversion to roughly $7 million per person. That sunset was repealed. But “permanent” in tax law means only “no expiration date written in” — the Congressional Research Service notes the exemption has been rewritten repeatedly since 2001, and a future Congress could lower it. If the per-person exemption reverted to approximately $7 million ($14 million combined), the same $25 million couple that owes $0 today would face roughly $4.4 million in tax on an $11 million taxable estate. That is the dormant risk portability hedges against: a ported DSUE locks in exemption that a survivor may need if the law turns less generous before they die.

What most coverage misses: portability is the cheapest exemption-doubling tool available

Estate planning content gravitates toward trusts — the credit shelter trust, the SLAT trust setup and ongoing fees, the GRAT mechanics and tax arbitrage. Those structures carry real cost: drafting fees, trustee administration, annual tax filings, and irrevocability that removes assets from the grantor’s control. Portability accomplishes one thing those trusts also do — preserving a deceased spouse’s exemption — at the price of a single estate tax return.

The data point that gets buried: the IRS deliberately made portability-only returns cheaper to produce. Under the regulations, an executor filing solely to elect portability for a below-threshold estate is not required to value every asset to the dollar. Property qualifying for the marital or charitable deduction can be reported at a good-faith estimate. That is a meaningful reduction in appraisal cost — the most expensive line item in a full Form 706. The five-year late-election window under Rev. Proc. 2022-32 further means a family that overlooks the deadline in the chaos following a death usually has years to fix it without a Private Letter Ruling. Compared to the cost and permanence of an irrevocable trust, portability is the low-friction option that most “what trusts should you set up” coverage skips past, because there is no product to sell around it. The Cluster Brief’s own sourcing guidance flags exactly this bias: insurance-company and attorney “what you should do” materials have commercial incentives that a return-only election does not feed.

Portability does have real limits, and pretending otherwise would be its own distortion. It does not shelter post-death appreciation the way a credit shelter trust can — assets that grow inside the survivor’s estate are taxed on their grown value, whereas a trust freezes the first spouse’s share at date-of-death value. It offers no creditor protection. And it does not apply to the generation-skipping transfer tax exemption, which is not portable and must be affirmatively allocated. For families whose assets are likely to outpace the inflation-indexed exemption, the will versus trust cost comparison matters more than portability alone. The honest framing is that portability is a floor, not a ceiling — cheap insurance that rarely substitutes entirely for structural planning at the top of the wealth range.

The $150k+ household calculus

For a household earning $150,000 and up, the portability question turns less on current income than on accumulated and projected net worth — and on geography. A dual-income professional couple in their forties with $4 million today, saving aggressively and invested in equities, can plausibly reach $15–20 million by the second death. Under 2026 federal law, that couple owes nothing if both exemptions are preserved and a real exposure if the first spouse’s DSUE is lost. The decision at the first death — file Form 706 or not — is therefore a decision made decades before the tax it affects. The cost of filing is a few thousand dollars in preparation. The cost of not filing, for an estate that later crosses $15 million, runs into the millions.

State law sharpens the math. Twelve states and the District of Columbia levy their own estate tax, and none offer portability — the estate versus inheritance tax by state breakdown shows thresholds as low as $2 million in Massachusetts and a notorious cliff in New York where exceeding 105% of the state exemption taxes the entire estate. A $150k+ household in a high-tax estate state faces exposure at net worth levels far below the federal $15 million, and federal portability does nothing for the state bill. For these families, federal portability is necessary but not sufficient; annual gifting strategy and the $19k exclusion and lifetime gifting become the tools that address state-level exposure the DSUE cannot touch. The practical threshold to watch is not income but the trajectory of net worth against both the federal exemption and whichever state regime applies — and for couples whose wealth sits substantially in a life insurance death benefit, an ILIT for life insurance tax and cost may keep that benefit out of the taxable estate entirely, a problem portability does not solve because it preserves exemption rather than shrinking the estate.