C-corps are taxed as separate legal entities and normally file their tax returns on form 1120.

Certain business entities such as limited liability companies or partnerships opt to be treated as an S corporations for tax purposes, which enable them to channel their net business income or loss through their owners or member’s individual tax returns via Form K1.

Partnership tax returns are filed on Form 1065 but it does not pay tax at the partnership level. Instead, partnerships are considered as a channel through which business profit or loss passes through to the respective partners via Form K1, and is included in their respective individual tax returns.

Non-profit organizations may include charitable organizations, religious institutions, trade and member organizations, universities, hospitals etc. and are normally exempt from federal and state income tax, except for unrelated business activities. Informational tax returns are filed mainly using form 990, 990EZ or 990N.