When one spouse dies, the survivor can often inherit not just assets but something less visible: the deceased’s unused federal estate-tax exemption. Combining the two exemptions can shield a far larger estate from tax when the second spouse dies, potentially saving heirs an enormous bill. The catch is procedural and unforgiving. The transfer, known as portability, happens only if an estate-tax return is filed for the first spouse, on time, even when no tax is owed and no return would otherwise be required. Miss the window, and the unused exemption is generally lost.
How portability moves an unused exemption
Federal law gives every person an exemption that can pass free of estate tax at death. When the first spouse dies without using all of theirs, the leftover amount, formally the deceased spousal unused exclusion, can be carried over to the survivor. The IRS Instructions for Form 706 explain that an executor elects to transfer that unused exclusion to the surviving spouse by completing and filing the estate-tax return. Once elected, the survivor adds the inherited amount to their own exemption, so the couple’s combined shelter follows the survivor rather than evaporating when the first spouse dies.
The effect can be large. A survivor who picks up a deceased spouse’s unused exclusion may be able to pass on roughly double the individual exemption, keeping a substantial estate out of the federal tax entirely. Without the election, only the survivor’s own exemption applies, and everything above it can be exposed to tax at the second death.
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The return that no one thinks they need to file
The trap is that portability requires a filing even when the first estate is nowhere near large enough to owe estate tax. Most estates fall below the threshold that forces a return, so families understandably assume there is nothing to file. But the election to transfer the unused exclusion is made only on Form 706, so an estate that would otherwise skip the return entirely must file one anyway to preserve the benefit. The IRS estate-tax guidance is explicit that portability is available only if the return electing it is filed. A grieving family that never files, believing a modest estate is exempt, can forfeit a shelter worth far more than the estate itself at the second death.
The election is also, by default, all or nothing on timing. The executor makes it by filing a complete and timely return; there is no separate short form or checkbox on the survivor’s own income-tax return that accomplishes the same thing.
What “on time” actually means
The deadline is tied to the first spouse’s death. A Form 706 is generally due within nine months of the date of death, and an executor can obtain an automatic six-month extension by filing the extension request before that deadline. Filing within that window is what makes the portability election valid; the Instructions for Form 706 describe the election as effective only when the return is filed timely, within nine months or before the end of an approved extension. An executor who lets the nine-month mark pass without either filing the return or securing the extension has, under the ordinary rules, missed the election.
Because the return can be detailed even for a simple estate, and because families are often dealing with far more pressing matters in the months after a death, the deadline slips past more often than it should. The paperwork feels unnecessary precisely because no tax is due, which is what makes the lost exemption so easy to overlook until it is too late.
The limited second chance for smaller estates
There is a relief valve, though a narrow one. For estates that were not otherwise required to file a return, the IRS offers a simplified method to make a late portability election. Under Revenue Procedure 2022-32, such an estate can file the return to elect portability up to the fifth anniversary of the decedent’s death, without seeking a private ruling. That extended path applies only to estates below the filing threshold; an estate large enough to have required a return in the first place does not get the five-year window and is held to the ordinary nine-month deadline.
The practical lesson for surviving spouses is to treat the estate-tax return as a decision to make deliberately, not one to skip because no tax is owed. Even a modest estate can carry an exemption worth preserving, and the difference between filing and not filing can determine whether a surviving spouse hands heirs a doubled shelter or a single one. The unused exemption is there to be claimed, but only by a family that files, and files before the clock runs out.
This article was produced with AI assistance and reviewed by The Financial Wire editorial team.
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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.
