All businesses except partnerships must file an annual income tax return.
Partnerships file an information return.
Which form you use depends on how your business is organized. See Table 2 to find out which return you have to file. You must pay the tax as you earn or receive income during the year. An employee usually has income tax withheld from his or her pay. If you do not pay your tax through withholding, or do not pay enough tax that way, you might have to pay estimated tax.