2021TurboTax Desktop Premier tax estimate penalty calculation line 38 of form 1040 is wrong.
The Tax Payments worksheet is correct, and shows the 4 periods of (04/15/21, 06/15/21, 09/15/21,01/18/21).
However, the software penalty calculation is expecting the first two payments to be paid by 04/15/2021. (This is probably a holdover of the 2020 rules that lumped the first payment (50%) to be 07/15/2020.)
Note, this error only occurs when the four estimate payments are NOT in equal amounts even though each payment is greater than 25% of the total required.
