Form 1120-S
The S corporation's yearly federal income tax return. It's due by the 15th day of the 3rd month after its year ends.
Form 1120-S, U.S. Income Tax Return for an S Corporation, is the return every S corp files, including an LLC that has elected S status. It reports the company's income and deductions but usually shows no tax due, because the profit passes to the shareholders.
The Form 1120-S instructions say it is due by the 15th day of the 3rd month after the end of the tax year. For a calendar year that is March 15, a month before personal returns. An extension is available.
With the return, the S corp gives each shareholder a Schedule K-1 showing their share of income, deductions and credits.
A default single-member LLC doesn't file a business return at all. Its profit goes on Schedule C. So the 1120-S is one of the costs an S election adds. StructureCost assumes $1,800 a year for the payroll service and this return together, an estimate rather than a quote.
Late filing draws a penalty per shareholder per month, so the deadline matters even when no tax is due.