This is a question about the federal estate tax in the United States.
Suppose a married man died in (let's say) 2021, when the estate tax exemption was $11.7 million. He leaves his entire estate to his wife taxfree. She dies in 2023, when the exemption is (say for simplicity) still $11.7 million. When the wife dies, she is entitled to both his and her exemptions, for a total of $23.4 million.
Now suppose instead that the man dies in 2021, leaving everything to his wife taxfree, and that she dies in 2026, after the exemption reverts to $5 million.
Once again, she is entitled to both exemptions. Does her total exemption amount to $11.7 million plus $5 million, or does it amount to $5 million plus $5 million? In other words, is the value of the ported exemption equal to the value of an exemption at the time of the first spouse's death or at the time of the second spouse's death?