Form 1120-S and Schedule K-1: the S corporation return

An S corporation files Form 1120-S, but the return works quite differently from a C corporation's. It is largely an information return: the corporation generally pays no federal income tax on its ordinary profit and instead passes that profit through to its shareholders, who are taxed on their own returns. What makes the S corporation distinctive is the interaction of that pass-through with the payroll obligation on owner-employees. This guide covers the return, the Schedule K-1, and the rules that shape both.

What Form 1120-S is

Form 1120-S, the U.S. Income Tax Return for an S Corporation, reports the corporation's income, deductions, and credits for the year, but the corporation generally does not pay income tax on the ordinary business income it reports. Instead each item flows through to the shareholders. The corporation reaches S status by making an election on Form 2553, and it must meet the S corporation conditions throughout — a domestic corporation with no more than 100 shareholders, only eligible shareholders, and a single class of stock. Losing any of those conditions ends the election and pushes the corporation back to C corporation treatment.

Schedule K-1: the shareholder's share

The corporation issues each shareholder a Schedule K-1 setting out that shareholder's share of ordinary business income, separately stated items, deductions, and credits, allocated in proportion to stock ownership. The shareholder reports those figures on their own return. As with a partnership, the income is taxed to the shareholder whether or not it was distributed — retained profit is still passed through and taxed. A difference from a partnership matters here: a distribution of profit from an S corporation to a shareholder is generally not itself subject to self-employment tax, which is a large part of why the structure is popular with owner-managed businesses.

Reasonable compensation comes first

That self-employment-tax advantage is exactly why the S corporation carries a rule the other pass-throughs do not. An owner who works in the business is an employee and must be paid reasonable compensation — a market-rate salary run through payroll, with employment taxes withheld — before taking profit distributions. The IRS scrutinises owners who take a token salary and a large distribution, and can recharacterise distributions as wages with back taxes and penalties. The detail of setting that figure is covered in reasonable compensation for S-corp owners. The practical consequence is that an S corporation must run payroll, which a sole proprietor does not.

Basis limits losses and shelters distributions

Each shareholder tracks their stock and debt basis in the corporation. Basis governs two things: a shareholder can deduct S corporation losses only to the extent of basis, with any excess suspended and carried forward; and distributions are generally tax-free only up to basis, with amounts beyond it treated as capital gain. Because these outcomes turn on a figure the corporation does not report for the shareholder, tracking basis is the shareholder's responsibility. How distributions and basis interact is set out in S corporation distributions and shareholder basis.

Deadline and entity-level exceptions

For a calendar-year S corporation, Form 1120-S is due by March 15, with a six-month extension to September 15 on Form 7004. Although the general rule is no entity-level income tax, there are narrow exceptions — notably the built-in gains tax that can apply to a corporation that converted from C to S status, and a tax on excess passive investment income in certain cases. These are situational rather than routine, but a corporation that recently converted or holds substantial passive income should check whether they apply. The federal return also sits alongside state filings, and not every state mirrors the federal pass-through, so an S corporation operating across states should confirm each state's treatment.

Sources

This guide is written against the official and clearly labelled professional references below. Rates, thresholds and portal procedures change between reviews, so open the primary source before relying on a figure.

• About Form 1120-S, U.S. Income Tax Return for an S Corporation (IRS)
• S Corporation compensation and medical insurance issues (IRS)
• Businesses (Internal Revenue Service)

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