A K-1 form, officially known as Schedule K-1, is a tax document used to report income, deductions, and credits from partnerships, S corporations, estates, and trusts. It provides detailed information about each partner's or shareholder's share of the entity's income, which they must report on their individual tax returns. The K-1 is essential for ensuring that all income is accurately reported to the Internal Revenue Service (IRS). Each entity must issue K-1 forms to its partners or shareholders, typically by March 15, to allow them to file their taxes on time.