Some forms and entities have due dates other than the well-known April 15th due date. The instructions for the each type of form used will have the appropriate due date(s) noted. In general, sole proprietor's schedule of income and expenses is attached to the 1040. Therefore, the due date is the same as the 1040.

A Corporation must generally use the calendar year, unless the entity can establish a business purpose for having a different tax year. The due date is usually March 15th.

A partnership generally must conform its tax year of the partners unless the partnership can establish a business purpose for having a different tax year. The tax year is the same as one or more partners that own (in total) more than a 50-percent interest in partnership profits and capital. If there is no majority interest tax year, the partnership must adopt the same tax year as that of its principal capital holder. Where neither condition is met, a partnership must use the calendar year. A limited Liability Company reporting as a partnership has the same tax year as a majority of its partners.

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