Per IRS Instructions for Form 1120-S U.S. Income Tax Return for an S Corporation, on page 21:
Purpose of Schedules
The corporation is liable for taxes on lines 22a, 22b, and 22c on page 1 of Form 1120-S. Shareholders are liable for tax on their shares of the corporation's income (reduced by any taxes paid by the corporation on income). Shareholders must include their share of the income on their tax return whether or not it is distributed to them. Unlike most partnership income, S corporation income isn't self-employment income and isn't subject to self-employment tax.
Schedule K. Schedule K is a summary schedule of all shareholders' shares of the corporation's income, deductions, credits, etc. All corporations must complete Schedule K.
On page 22:
Schedule K-1.Schedule K-1 shows each shareholder's separate share. Attach a copy of each Schedule K-1 to the Form 1120-S filed with the IRS. Keep a copy for the corporation's records and give each shareholder a copy.
Give each shareholder a copy of the Shareholder's Instructions for Schedule K-1 (Form 1120-S) or specific instructions for each item reported on the shareholder's Schedule K-1.
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