The reality is filing the Form 706 is not only best practice ... the law notably increased the unified federal gift and estate tax exemption amounts (and generation-skipping transfer tax exemption ...

Portability: If the decedent was married, the executor might elect to transfer any unused federal estate tax exemption to the surviving spouse by filing a timely Form 706, even if no tax is due.

In this case, they are deductible only for determining the taxable estate for federal estate tax purposes and must be claimed on IRS Form 706, United States Estate (and Generation-Skipping ...