When one spouse dies without using all of the federal estate-tax exemption, the unused portion does not have to disappear. A rule called portability lets a surviving spouse claim what the late partner left behind, stacking two exemptions into a combined shelter approaching $30 million in 2026. The catch is that the benefit is not automatic. It is forfeited unless the executor of the first spouse’s estate files a specific federal return and makes the election on time, even when the estate is far too small to owe any tax.
How portability works
Each person has a lifetime estate-tax exemption, set near $15 million per person in 2026. When the first spouse dies, that estate often uses only a fraction of the figure. Portability allows the leftover amount, known as the deceased spousal unused exclusion, to move to the surviving spouse. The survivor then adds it to their own exemption, which is how a couple’s combined shelter can reach roughly $30 million.
A simple example shows the stakes. If the first spouse to die leaves an estate that uses $3 million of the exemption, about $12 million of unused exclusion remains. Ported to the survivor, that amount sits on top of the survivor’s own exemption, sheltering a far larger combined estate than one exemption alone could cover. The federal estate-tax rules that set the per-person exemption are described in the IRS estate-tax overview, and portability is the mechanism that lets a couple use both halves rather than wasting the first.
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The election that is easy to miss
Portability only happens if it is claimed. The executor of the first spouse’s estate must file a federal estate-tax return, Form 706, and make the portability election on it. According to the IRS instructions for Form 706, the return is generally due nine months after the date of death, with an automatic six-month extension available on request. Crucially, this return must be filed to transfer the unused exclusion even when the estate is nowhere near the taxable threshold and owes nothing.
That requirement is exactly where families lose the benefit. Because most estates fall well below the exemption, survivors and executors often assume no filing is needed and skip Form 706 entirely. The IRS frequently asked questions on estate taxes make the point directly: a return must be filed to elect portability regardless of the size of the gross estate, and an estate can also choose to opt out. Doing nothing is not neutral. It quietly forfeits an exemption that could be worth millions to the survivor later.
A second chance for smaller estates
The nine-month deadline is unforgiving, but the IRS has built in relief for the estates most likely to overlook the election. Under a simplified procedure in Revenue Procedure 2022-32, an estate that was not otherwise required to file a return can still make a late portability election up to five years after the date of death. The relief applies only to estates below the filing threshold and only for the portability election itself, but for many surviving spouses it is a meaningful safety net when the original deadline slipped by unnoticed.
Even with that cushion, waiting carries risk. The five-year window can close before a survivor realizes the exemption was left on the table, and gathering date-of-death valuations years later is harder than doing it promptly. Filing the return soon after the first death, even when no tax is due, preserves the option cleanly rather than relying on a relief procedure with its own limits.
Why it can matter years later
A surviving spouse may have no taxable estate on the day the first partner dies, which makes the filing feel pointless. Circumstances change, though. Investments and a home can appreciate for decades, a business can grow, or an inheritance or legal settlement can arrive. An estate that looked modest at the first death can push past a single exemption by the time the survivor dies, and by then the chance to capture the first spouse’s unused amount is gone. Locking in the ported exclusion early preserves flexibility that is inexpensive to keep once it is in place.
Remarriage adds a wrinkle that catches some survivors off guard. A surviving spouse can generally use only the unused exclusion of their most recent deceased spouse, so a person who ports an exemption from a first spouse and then remarries can lose that ported amount if the second spouse also dies without leaving unused exclusion. The interplay is technical, but it underscores why the ported figure should be documented and folded into later planning rather than treated as a one-time formality to be forgotten.
Filing Form 706 solely to preserve portability does carry an upfront cost. The return is detailed, requires valuing every asset in the estate as of the date of death, and often means hiring an accountant or estate attorney, an expense that can reach into the thousands even for a modest estate that owes no tax. Families weigh that outlay against how likely the survivor’s estate is to grow past a single exemption. For a younger survivor with appreciating assets, the filing is usually worth it; for an older survivor with a small, stable estate, the calculus is closer.
Portability is not the only tool for couples, and it has limits worth knowing. It applies to the estate and gift exemption but not to the separate generation-skipping transfer exemption, which cannot be ported and still requires its own planning. For that reason some families continue to use trusts alongside or instead of portability. But for a large share of married couples, simply filing the return after the first death is the most direct way to keep both exemptions in the family rather than surrendering one of them by default.
Before portability became a permanent feature of the tax law in 2013, couples typically relied on a credit-shelter trust, sometimes called a bypass trust, to capture both exemptions. That approach still has uses, including keeping future growth of the first spouse’s share out of the survivor’s taxable estate and protecting assets for children from a prior marriage. Portability simplified the picture for many families by making a trust unnecessary just to preserve the exemption, yet the two tools solve overlapping problems and are sometimes used together on the advice of an estate planner.
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This article was researched and drafted with AI assistance and reviewed against the linked primary sources.
David M. Keller is a finance writer based in Columbus, Ohio, covering personal finance and consumer-focused economic topics. He earned his degree in journalism from Ohio University and began his career reporting on local business and economic trends for a regional media outlet. Since then, he has contributed to a variety of online publications, focusing on clear, practical coverage of topics such as cost of living, debt, and everyday financial decision-making.
