It is a best practice to pay federal and state taxes as incurred throughout the year. Tax withholding for federal and state purposes can be adjusted at any time throughout the year.
Alternatively, by making timely, quarterly estimated payments in compliance with the employee tax withholding state-wide standards, the underestimated tax penalty calculation page would not be necessary. For Pennsylvania state taxes, for years, the rate is 3.07%.
Go to Pennsylvania's Online Services to learn more about your options for Making Pennsylvania Tax Payments.
To calculate the federal withholding, use IRS Withholding Estimator or try the TurboTax Paycheck Checkup site:
I don't think you understand. My income varies significantly throughout the year, so I make federal and PA estimated payments based upon the income for the given period. TuboTax federal form 2210 works just fine. As I indicated earlier, TurboTax PA Rev1630 is a nightmare. It is difficult to access, it doesn't transfer payments properly (in 2018), and it calculates incorrectly (to the tune of $170 in 2019).
Here's an additional desktop Turbotax 2021 bug relating to PA Rev 1630:
The form is included in my return despite my selecting the option to let the PA Dept of Revenue calculate any underpayment penalty. Despite my attempts to delete the Rev 1630 form from my return, Turbotax will not do so.
Please fix this bug.