What would be the reason somebody would have to pay in to the federal and to the state?

[BillM223]

The main reason would be that somebody is underwithholding on their wages.

[VolvoGirl]

Or if you have other income like interest, dividends, investment or self employment that doesn’t have withholding taken out.   You might need to send I. Quarterly estimated payments to cover extra income.   Or if you took a IRA or retirement distribution.  Even if you have withholding taken out it might not be enough to cover the extra tax on your total income.