@fanfare
To answer your questions:
"If you are in the same bracket both years, it doesn't matter if you use the LSE method (as described in IRS Pub) or you don't use it. (unless you're right on the edge of the next higher bracket in one year)"
A true statement, agree. I moved from the 22% bracket in 2020 to the 24% bracket in 2021. 2% is not a big difference. Am not near the edge of the brackets - this Lump Sum does not cause a crossing of the bracket boundaries.
"The easiest method is to just assign all the benefits to this year.
Do I read correctly that you're saying if you do that, TurboTax gives the correct tax?"
That is a Yes if by "correct tax" you mean the figure computed by the IRS. Both TT and the IRS seem to be applying the 24% marginal tax rate.
At this point we are talking a small amount of money versus the time I would have to spend with the IRS on a challenge. But I do intend to pursue the apparent math error with TurboTax.
