Schedule K-1 (Form 1120-S) is the statement an S corporation gives each shareholder every year showing that owner's share of the company's income, deductions, credits, and other tax items. The S corporation itself generally pays no federal income tax; the K-1 is the document that moves the year's results from the corporate return onto the owners' personal returns, where the tax actually gets paid. Each shareholder's share is strictly pro rata: stock ownership percentage, applied day by day across the year. A 60% shareholder gets 60% of every line. The corporation files the K-1s with its Form 1120-S and must furnish them to shareholders by the return's deadline, March 15 for calendar-year companies, or September 15 on extension. One point surprises every new S corporation owner: the K-1 reports your share of profit whether or not any cash was distributed to you. Income is taxed as earned, not as paid out.
What the boxes report
Box 1 carries the shareholder's share of ordinary business income or loss, the pass-through profit after expenses and after shareholder-employee salaries. That salary itself is not on the K-1; it arrives separately on a W-2, and the K-1 picks up what is left. The rest of the form keeps items separate whenever a shareholder's personal limits could apply differently: interest and dividend income, capital gains, Section 179 deductions, charitable contributions, and credits each get their own lines. Box 16 reports items affecting shareholder basis, including distributions under code D. Box 17 code V points to an attached statement with the Section 199A detail, the business income, W-2 wage, and property figures a shareholder needs to compute the qualified business income deduction on their own return. Unlike a partner's K-1 from Form 1065, none of the ordinary income on an 1120-S K-1 is subject to self-employment tax, which is the arithmetic heart of the S corporation strategy.
Where the numbers land on your 1040
K-1 amounts do not get typed onto Form 1040 directly. Box 1 ordinary income flows to Schedule E, Part II, and from there into total income. Interest and dividends move to Schedule B, capital gains to Schedule D, and credits to their own forms. The Box 17 statement feeds Form 8995 or 8995-A for the QBI deduction, which for many owners cuts the effective rate on pass-through profit by a fifth. Whether a loss in Box 1 is deductible at all depends on a gauntlet of limits applied in order: the shareholder must have basis, must be at risk, and must clear the passive activity rules if they do not materially participate. A loss that fails a limit is not gone, it is suspended and carried forward until the limit opens up.
Basis: the gatekeeper
Stock basis is the running measure of what a shareholder has put into the company and left in it, and the K-1 cannot be used properly without it. Basis starts with what you paid or contributed for the stock, rises with the income the K-1 allocates to you, and falls with losses and with distributions. Two consequences follow. Losses on the K-1 are deductible only up to basis. And distributions are tax-free only up to basis; cash taken out beyond it is capital gain. This is why taking every dollar out of a marginally profitable S corporation can quietly generate a tax bill. Shareholders, not the corporation, are responsible for tracking their own basis, and the IRS now requires Form 7203 to be attached to the 1040 in the years it matters, including any year the shareholder claims a loss, receives a distribution, or disposes of stock. Debt basis from money the shareholder personally lent the corporation is tracked separately and can absorb losses after stock basis runs out; loans the company owes a bank never count.
Timing, late K-1s, and errors
The K-1 arrives on the corporation's schedule, not the shareholder's, and an extended 1120-S legally pushes K-1 delivery to mid-September, five months past the shareholder's own April deadline. The standard answer is for the shareholder to extend their 1040 and pay their expected tax by April 15 using a reasonable estimate. Filing without the K-1 and amending later is possible but usually costs more in preparation than the extension would have. When a K-1 is wrong, the fix belongs at the corporate level, an amended 1120-S with corrected K-1s, because the IRS matches what the corporation filed against what each shareholder reported. A shareholder who simply reports different numbers than their K-1 shows is volunteering for a notice.