Understanding Portability for Estate and Gift Tax

Portability of estate and gift tax enables a surviving spouse to inherit any unused portion of their deceased spouse’s federal estate and gift tax exemption. So, if one spouse doesn’t utilize their full exemption, the surviving spouse can effectively double their exemption amount with regard to estate tax liability.

For married couples, portability offers a powerful mechanism to preserve unused tax exemptions and minimize transfer tax liability. However, it is frequently misunderstood, underutilized, or improperly elected—sometimes at substantial cost. This article provides an in-depth legal analysis of portability, including its statutory framework, mechanics, planning implications, and limitations.

What Is Portability?

Under federal law, each individual is entitled to a lifetime exemption from estate and gift taxes. The exemption increased to $15 million per person in 2026, pursuant to the One Big Beautiful Bill Act. Traditionally, this exemption was “use it or lose it.” If the first spouse to die did not fully use their exemption, the unused portion was lost.

Portability, which was first authorized under the Tax Relief, Unemployment Insurance Reauthorization and Job Creation Act of 2010, changed that result. It allows a surviving spouse to use any unused exemption from a deceased spouse, known as the Deceased Spousal Unused Exclusion (DSUE). In practical terms, this means a married couple can combine their exemptions—even if all assets pass outright to the surviving spouse.

How Portability Works and Why It Can Be Beneficial

When the first spouse dies, their estate calculates how much of their exemption was used. Any unused portion can be transferred to the surviving spouse, provided that a timely election is made. This effectively increases the amount the surviving spouse can transfer during life or at death without incurring federal estate or gift tax. For many couples, this can mean the ability to shield tens of millions of dollars from federal estate tax.

Portability offers several important benefits for married couples, including:

• Portability allows families to take full advantage of both spouses’ exemptions without requiring complex trust structures. In many cases, assets can pass directly to the surviving spouse while still preserving tax benefits.
• Portability provides flexibility. The surviving spouse retains control over the assets and can decide later how and when to transfer wealth to the next generation.
• Portability can serve as a safeguard in a changing tax environment. While the estate tax exemption is $15 million per person in 2026, it was $5,490,000 in 2017, and only $600,000 in 1997.

Electing Portability

Portability is not automatic. Rather, it must be affirmatively elected by filing Form 706 (United States Estate Tax Return) after the first spouse’s death. This requirement is often overlooked, especially when no estate tax is due. Many assume that because the estate is below the taxable threshold, no filing is necessary. In reality, failing to file can result in the permanent loss of the unused exemption.

Current rules provide some flexibility, allowing additional time (up to 5 years) to file in certain circumstances. However, relying on extensions or relief provisions is risky. The safest course is to evaluate the need for filing promptly after a spouse’s death, even for moderately sized estates.

Potential Portability Pitfalls

Despite its advantages, portability is not a complete substitute for traditional estate planning. One key limitation is that portability does not apply to the generation-skipping transfer (GST) tax exemption, which is often critical for multigenerational planning. Separate strategies are required to address GST tax exposure.

Portability also does not protect future appreciation of assets. If all assets pass outright to the surviving spouse, any growth in value will be included in the surviving spouse’s estate. In contrast, certain trust structures can remove that appreciation from the taxable estate. In addition, portability can be affected by remarriage. If a surviving spouse remarries and the new spouse later dies, the surviving spouse may only use the unused exemption from the most recent spouse.

Finally, clients should be aware that state estate taxes—such as those imposed in Massachusetts—often have lower exemption thresholds and generally do not recognize portability. State-level planning may still be necessary even when federal estate tax is not a concern.

Based on these potential limitations, portability should be evaluated in light of:

• Client net worth trajectory
• Likelihood of remarriage
• State estate tax exposure
• Desire for asset protection or control
• GST planning needs

How We Can Help

Portability has made estate planning more flexible and, in some cases, more straightforward for married couples. At the same time, it introduces important decisions that must be addressed promptly. If you have questions about how portability applies to your situation, we encourage you to consult with a member of Scarinci Hollenbeck’s Tax, Trusts & Estates practice group.