A return with no tax due, worth millions later.

The facts, in one place.

Six quotable sentences on portability, 2026 figures.

1. Each person can leave $15 million free of federal estate tax in 2026. Whatever a first spouse does not use, because everything went to the survivor or to charity, can be added to the survivor's own exclusion (§ 2010(c)(2), (4)), but only if the first estate files an estate tax return and elects it (§ 2010(c)(5)).
2. Without the election, the unused amount is lost when the survivor dies with more than their own exclusion. With it, a couple can shelter $30 million in all, at 40% on the excess.
3. Example: the first spouse leaves everything to the survivor, using none of the exclusion. If the survivor later dies with $20 million, the federal tax is $2,000,000 without the election and $0 with it.
4. The return is due nine months after the death, but an estate not otherwise required to file may make the election on a return filed within 5 years (Rev. Proc. 2022-32). After that, the amount is gone.
5. Illinois has no portability: its $4 million exclusion is per person and unused amounts are lost at the first death, which is why Illinois couples still use trusts at the first death to preserve the first spouse's exclusion.
6. The election costs a return, an appraisal, and a fee, at a time when the estate seems too small to matter; the survivor's estate grows, the law can change, and the filing is the only way to keep the option.

What the election is worth.

Nothing to the survivor at the first death; everything turns on how large the survivor's estate becomes.

How portability works.

Every person has a federal estate tax exclusion, and a married couple has two. When the first spouse dies leaving everything to the survivor, the marital deduction means no tax is due and none of the first spouse's exclusion is used. Before portability that exclusion was simply lost, and couples preserved it with a trust at the first death. Now the survivor may add the unused amount to their own, but only if the first spouse's executor files an estate tax return and makes the election, on a return that is otherwise unnecessary.

The election is easy to skip. The estate seems small, no tax is due, and the return costs money. Its value appears years later, when the survivor's estate has grown or the exclusion has been cut by a change in the law, and by then the deadline has passed. Illinois has no portability at all: its exclusion is per person and unused amounts are lost, which is why Illinois couples still plan around the first death with trusts. The calculator shows the federal tax on the survivor's projected estate with and without the election, and the Illinois tax that the election does not touch.

Methodology.

1. Inputs. What the first spouse left to anyone other than the survivor or charity, plus lifetime taxable gifts (the exclusion the first estate used), and the survivor's projected estate.
2. The unused amount. The federal exclusion for the year less the first estate's taxable estate, never below zero (§ 2010(c)(4)).
3. The survivor's exclusion. The basic exclusion alone, or the basic exclusion plus the unused amount with the election (§ 2010(c)(2)).
4. The tax. The survivor's estate above the exclusion at the top rate, each way; Illinois from the estate engine already on this site, the same either way.
5. Validation. A first spouse who used nothing against a survivor with twenty million; a first estate that used part of the exclusion against a survivor still under their own; and an Illinois estate that owes Illinois tax either way. A transcription error fails the build.
6. Not modeled. Deductions and credits in the survivor's estate, growth in the exclusion or a change in the law, lifetime gifts after the first death, remarriage and the last-deceased-spouse rule, the generation-skipping exemption (which is not portable), and other states' estate taxes. Educational, not advice.

Sources.

1. 1. United States Code (Cornell LII), 26 U.S.C. § 2010(c)(4) and (5) — Deceased spousal unused exclusion amount; the election. That a surviving spouse's exclusion is the basic exclusion plus the last deceased spouse's unused amount (c)(2); the definition of that unused amount as the deceased spouse's basic exclusion less their taxable estate and adjusted taxable gifts (c)(4); and that it is available only if the executor of the first estate files a timely estate tax return and makes the election (c)(5). Retrieved September 6, 2026; verified September 6, 2026.
2. 2. Internal Revenue Service, Rev. Proc. 2022-32 — Simplified method for a late portability election. That an estate not otherwise required to file may make the portability election on a return filed within five years of the death, without a private letter ruling. Retrieved September 6, 2026; verified September 6, 2026.
3. 3. Internal Revenue Service, Instructions for Form 706 — Portability of the deceased spousal unused exclusion. How the election is made (filing a complete return), the computation of the unused amount on Part 6, and that the election is irrevocable once the due date passes. Retrieved September 6, 2026; verified September 6, 2026.

Revision history.

The record's history; the exclusion and the Illinois computation come from the estate record.

September 6, 2026

First release: the unused exclusion a first death leaves, the survivor's exclusion with and without the election, the federal tax each way on the survivor's projected estate, and the Illinois tax that the election does not change.

Canonical address: https://consideratecapital.com/tools/portability-election-calculator