What is portability of the spousal estate tax exemption?

Portability lets a surviving spouse inherit the unused portion of their deceased spouse's federal estate tax exemption. Each person has an exemption (about $13.99 million in 2025); if the first spouse to die uses only part of it, the leftover – called the DSUE, deceased spousal unused exclusion – transfers to the survivor, potentially nearly doubling their own exemption. The crucial catch: portability is not automatic. The executor must elect it by filing a federal estate tax return (Form 706) within nine months of death (extensions available), even when no tax is owed. Many families skip this filing because the estate is small, then regret it if the survivor's estate later grows above the exemption. If there's any chance the combined estate could approach the exemption, file to preserve portability. Note portability applies to the estate tax exemption but not the GST exemption.