What Is an S Corp? Definition, Taxes, and How to File

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An S corporation (S corp) is a corporation, or an eligible entity such as an LLC, that has elected to be taxed under Subchapter S of the Internal Revenue Code. With that election, the business generally pays no federal income tax itself. Its income, losses, deductions and credits pass through to its shareholders, who report their shares on their personal returns and pay tax at their own rates. The business keeps the limited liability of a corporation while avoiding the “double taxation” that applies to a regular C corporation.

What the “S” Stands For

The name comes from the tax code, not from state corporate law. Congress created the S corporation option in 1958 so that small, closely held businesses could operate as corporations without paying corporate income tax.

A corporation that has not made the election is taxed under Subchapter C, which is where the term “C corporation” comes from. Both are corporations under state law. They differ in how the federal government taxes them.

How an S Corp Is Taxed

Pass-through income and Schedule K-1

An S corp calculates its income and expenses much like any other business. Instead of paying tax on the resulting profit, it allocates each item to shareholders in proportion to their ownership. If you own 30% of the shares, you report 30% of the ordinary business income, 30% of any capital gains, 30% of charitable contributions and so on.

The corporation reports these allocations on Schedule K-1, one per shareholder. Shareholders use the K-1 to complete their individual Form 1040 and pay tax at ordinary income rates on their share of business income (or at capital gains rates on items that keep that character, such as long-term capital gains).

Shareholders owe tax on their share of profit whether or not the corporation distributes any cash. If an S corp earns $200,000 and keeps all of it in the bank to fund expansion, a 50% owner still reports $100,000 of income. Owners sometimes call this “phantom income,” and many S corps make at least enough distributions to cover the owners’ tax bills.

Because S corp income passes through, owners may also qualify for the qualified business income (QBI) deduction under Section 199A, which was introduced by the 2017 Tax Cuts and Jobs Act. The deduction has income thresholds and limits, including restrictions for certain service businesses, so eligibility depends on the owner’s full tax picture.

Taxes an S corp can still owe at the entity level

“No corporate tax” is the general rule, not an absolute one. An S corp can owe federal tax in a few situations:

• Built-in gains tax. If a C corporation converts to S status and then sells assets that had appreciated while it was a C corp, the corporation can owe corporate-level tax on that built-in gain if the sale happens within the recognition period after conversion.
• Excess net passive income tax. An S corp that has accumulated earnings and profits from its C corp years can owe tax if its passive investment income (such as rents, royalties, interest and dividends) exceeds 25% of gross receipts. If that condition persists for three consecutive years, the S election terminates.
• Payroll taxes. An S corp that pays wages owes the employer share of Social Security and Medicare taxes, plus federal and state unemployment taxes, like any employer.

State treatment varies as well. Some states follow the federal pass-through approach. Others impose franchise taxes, minimum taxes or entity-level taxes on S corps, and a few do not recognize the federal election in the same way.

Basis, losses and distributions

Each shareholder tracks a basis in the company: roughly, what they contributed plus their share of income, minus their share of losses and distributions received. Basis matters in two ways.

First, losses passed through on the K-1 are deductible only up to the shareholder’s stock basis plus any basis in loans the shareholder made directly to the corporation. Losses above that amount carry forward until basis is restored.

Second, distributions are generally tax-free to the extent of the shareholder’s stock basis, because the shareholder has already paid tax on that income as it was earned. A distribution that exceeds basis is taxed as a capital gain. S corp distributions are not “dividends” in the C corp sense, and a corporation with leftover earnings from prior C corp years follows more complex ordering rules.

IRS Requirements for S Corp Status

A business must meet all of these conditions to elect and keep S corp status:

1. Domestic entity. It must be a corporation, or an entity eligible to be taxed as one (such as an LLC), organized in the United States.
2. No more than 100 shareholders. Members of a family can be treated as a single shareholder for this count.
3. Eligible shareholders only. Shareholders must be individuals who are U.S. citizens or residents, certain trusts, estates, or certain tax-exempt organizations such as 501(c)(3) charities. Partnerships, corporations and nonresident aliens cannot be shareholders.
4. One class of stock. All shares must carry identical rights to distributions and liquidation proceeds. Differences in voting rights are permitted, so a company can have voting and nonvoting shares and still have one class of stock.
5. Not an ineligible corporation. Certain financial institutions, insurance companies and domestic international sales corporations cannot elect S status.

Breaking any requirement, for example by selling shares to a nonresident alien or to another corporation, can terminate the election. Disproportionate distributions can create a problem too, because they may be treated as evidence of a second class of stock.

How to Set Up an S Corp

Becoming an S corp takes two layers of paperwork: state formation, then the federal tax election.

1. Form the entity under state law. File articles of incorporation (for a corporation) or articles of organization (for an LLC) with the secretary of state where the business is based. This usually involves a filing fee and naming a registered agent to receive legal notices.
2. Get an Employer Identification Number (EIN) from the IRS.
3. Adopt governing documents. Corporations adopt bylaws, appoint a board of directors and elect officers. LLCs adopt an operating agreement.
4. File Form 2553, Election by a Small Business Corporation. All shareholders must sign the consent statement, an officer must sign the form, and the corporation’s exact name, address and other required details must be complete. For the election to apply to the current tax year, the form generally must be filed no more than two months and 15 days after the start of that tax year, or at any time during the preceding year. A late election may still be accepted if the business shows reasonable cause.
5. Check state requirements. Some states require their own S election filing or have separate rules.
6. Set up payroll for any shareholder who works in the business, so that reasonable compensation runs through W-2 wages with withholding.

An LLC that elects S corp status can file Form 2553 directly. It is then treated as having elected to be taxed as a corporation as well, without filing a separate classification form.

Filing S Corp Taxes

Form 1120-S, U.S. Income Tax Return for an S Corporation, is the annual federal return. It reports the company’s income, deductions, credits and the amounts allocated to shareholders. Every S corp with an accepted election must file it, even in a year with no profit, because the IRS uses it to match what shareholders report on their own returns.

Key filing points:

• Due date: the 15th day of the third month after the end of the tax year. For a calendar-year S corp, that is March 15.
• Schedule K-1: prepared for each shareholder and furnished to them, so they can file their personal returns.
• Extension: filing Form 7004 by the original due date gives an automatic six-month extension to file the return. It does not extend time to pay any tax the corporation itself owes.
• Payroll filings: quarterly Form 941 and annual W-2s for shareholder-employees and other staff, plus state payroll and unemployment filings.
• Shareholder estimated taxes: because no tax is withheld on pass-through profit, owners often need to make quarterly estimated payments on their personal accounts.

Penalties for late filing of Form 1120-S are assessed per shareholder, per month, so a missed deadline costs more as the number of owners grows.

Reasonable Compensation and the Payroll Tax Savings

A sole proprietor, or an LLC owner taxed as a sole proprietor or partnership, pays self-employment tax on nearly all business profit. The combined rate is 15.3%: 12.4% for Social Security (up to the annual wage base) and 2.9% for Medicare, with an additional Medicare tax at higher incomes.

An S corp owner who works in the business is an employee. Payroll taxes, at the same combined 15.3% split between employer and employee, apply to their salary. Profit distributed above that salary is not subject to payroll tax. It is still subject to income tax.

The IRS knows this creates an incentive to set salaries artificially low and pay the rest as distributions. The rule is that shareholder-employees must receive reasonable compensation for the services they perform before taking distributions. “Reasonable” is judged by facts such as the owner’s duties, time spent, experience, and what comparable businesses pay for similar work. If the IRS concludes that distributions were disguised wages, it can reclassify them and assess back payroll taxes, interest and penalties.

Hypothetical example

Assume a consulting business earns $150,000 of net profit before any owner salary, in a year when the owner’s earnings are below the Social Security wage base. The figures below cover federal payroll and self-employment tax only, not income tax.

Taxed as a sole proprietorship:

• Self-employment tax applies to 92.35% of net earnings: $150,000 × 0.9235 = $138,525.
• Self-employment tax: $138,525 × 15.3% ≈ $21,194.

Taxed as an S corp paying the owner a $70,000 salary (assumed reasonable for the role):

• Payroll tax on salary: $70,000 × 15.3% = $10,710 (half paid by the company, half withheld from the owner’s pay).
• The employer half ($5,355) is a business deduction, so pass-through profit is $150,000 − $70,000 − $5,355 = $74,645, reported on the owner’s K-1 and taxed as ordinary income with no payroll tax.

Difference: about $10,484 in payroll and self-employment tax in this example.

That gross figure is not the net saving. Against it the owner sets the costs of running payroll, a more complex business tax return, state fees or entity-level taxes, unemployment taxes on the salary, and compliance time. A higher reasonable salary shrinks the saving, and a business with modest profit may find the costs outweigh it. The salary choice can also affect the QBI deduction and retirement plan contribution limits, which are often tied to W-2 wages.

Advantages of an S Corp

• Single level of tax and possible payroll savings. Profit is taxed once on shareholders’ returns, and distributions above a reasonable salary are not subject to Social Security and Medicare taxes.
• Pass-through losses and tax-free distributions. Losses can offset other income within basis and other loss limits, and distributions of already-taxed profit are generally not taxed again up to basis.
• Limited liability. As with any corporation or LLC, shareholders’ personal assets are generally protected from business debts and lawsuits against the company, provided the business follows the formalities that keep that protection intact.
• Corporate structure and transferability. Ownership is represented by shares, which can make it straightforward to transfer interests or bring in additional eligible owners.

Disadvantages and Limitations

• IRS scrutiny of compensation. Low salaries paired with large distributions draw attention, and the reasonable-compensation standard requires judgment and documentation.
• Strict allocation rules. Profits, losses and distributions must follow ownership percentages. A partner-style deal where one owner gets 60% of profit while owning 50% of the company is not possible without risking the one-class-of-stock rule.
• Ownership restrictions. The 100-shareholder cap and the ban on corporate, partnership and nonresident alien shareholders rule out typical venture capital and institutional investment, and can complicate estate planning and international ownership.
• Risk of termination. Ineligible shareholders, a second class of stock, election defects, or excess passive income can end S status. Inadvertent errors can often be fixed through IRS relief procedures if caught and corrected promptly. A revoked or terminated election generally cannot be made again for five years without IRS consent.
• Formalities and cost. A corporation needs a board, bylaws, shareholder meetings and minutes. All S corps face annual state reports and fees, payroll processing and a separate business return.
• Tax on undistributed profit. Owners pay tax on income the company retains, which can strain personal cash flow.

S Corp vs. C Corp

Both are corporations under state law with the same liability protection, governance structure and ability to issue stock. The difference is federal tax treatment and ownership flexibility.

A C corporation pays federal corporate income tax on its profits at a flat 21%. When it pays dividends from after-tax profit, shareholders pay tax again. An S corporation generally pays no federal income tax; profit is taxed once on shareholders’ returns.

A simplified hypothetical, ignoring state taxes and assuming all profit is paid out:

Actual results depend on the owner’s bracket, whether the C corp retains earnings instead of paying dividends, the QBI deduction, and state taxes. A C corp that reinvests most of its profit and pays few dividends may be taxed less in the near term than an S corp whose owners pay personal rates on all profit.

C corps have no limit on shareholder count or type and can issue multiple classes of stock, such as preferred shares for investors. That is why companies planning to raise venture capital or go public usually organize as C corps. An S corp can convert to C corp status by revoking its election, though built-in gains and the five-year waiting period matter if the owners might later want to switch back.

S Corp vs. LLC

An LLC is a legal entity formed under state law. An S corp is a tax election. They are not competing entity types in the strict sense, because an LLC can elect to be taxed as an S corp.

Without an election, a single-member LLC is taxed as a sole proprietorship and a multi-member LLC as a partnership. Both are pass-through treatments, but owners pay self-employment tax on their share of business profit. An LLC also has more flexibility than an S corp:

• No limit on the number of members, and members can include corporations, partnerships and foreign persons.
• Profits and losses can be allocated in proportions that differ from ownership, subject to partnership tax rules.
• Fewer required formalities: no board, no mandatory shareholder meetings or minutes in most states.

Both structures offer limited liability, and both can qualify for the QBI deduction. LLCs are simpler to form and maintain, which is why sole proprietors and small professional groups often use them. Their growth financing tends to rely on loans and member contributions rather than outside equity.

An LLC owner typically considers the S corp election when profit is high enough that the payroll tax savings on distributions exceed the extra cost of payroll and compliance.

FAQs

The Bottom Line

The S corp election suits small, closely held businesses whose owners are eligible shareholders and whose profit is high enough to make payroll tax savings worthwhile. Those savings shrink with a higher reasonable salary and must cover added costs for payroll, tax filings and state fees. Companies seeking venture capital or multiple stock classes usually fit better as C corps, while owners wanting flexible allocations may prefer an LLC taxed as a partnership.