satisfy the safe harbor of 110% of last year's tax withholding."
It is not 110% of prior withholding.
It is 110% (or 100%, given low enough prior AGI ) of prior year's tax that must be withheld to use this strategy for a large windfall.
For a large windfall, tax will be due and even without penalty thanks to withholding, some Estimated Tax may be prudent.
@samury
@dmertz
