I cannot find the source of form 1040 line 25c which was generated

[rjs]

The amount on Form 1040 line 25c is probably Additional Medicare Tax withholding from Form 8959 line 24. If that's not what it is, then it comes from the Tax Payments Worksheet lines 18a through 18e.

Since you are using TurboTax Online, the only way to see Form 8959 or the Tax Payments Worksheet is to print or create a PDF of your tax return. To see the Tax Payments Worksheet you have to select the option to include all government and TurboTax worksheets.

[VolvoGirl]

25C can also come from W2-G gambling and Schedule K-1.