Could be the extra Medicare tax, or if you have some Self-Employment income, could be the added Self Employment tax.
Yeah, the suggestion to use Desktop software instead of the "Online" software, on a full Windows or MAC computer does let you see the calculation forms at any time (Windows has much better operation/fewer bugs).
BUT
You can also see all the forms, including the tax calculations, with the "Online" software, by going to the Print Center and downloading a copy of your tax file as a PDF...but you need to get the copy with all forms and worksheets, since the file-only copy is just the filing sheets. Of course, you have to pay for the software you are using before you can get that PDF.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
