Two corporations can look identical from the outside and file completely differently, because one is taxed in its own right and the other passes its results to its owners.
The choice is usually made early, on the first year's numbers, and then lived with for a long time. What it costs or saves changes as the business grows, takes on owners, or approaches a sale.
This covers how the two returns differ in practice, what each treatment means for the owners, the eligibility conditions one of them carries, and the points at which the original choice is worth revisiting.
Both C-corporations and S-corporations are incorporated entities formed under state law. The difference lies in how they are taxed at the federal level. A C-corporation files Form 1120 and pays entity-level tax. An S-corporation files Form 1120-S but generally pays no entity-level tax, income passes through to shareholders who report it on their personal returns. Choosing the right structure (or switching) can save or cost tens of thousands of dollars.
Side-by-Side Comparison
| Feature | C-Corporation (Form 1120) vs S-Corporation (Form 1120-S) |
|---|---|
| Entity-level tax | C-Corp: Yes, 21% flat rate. S-Corp: Generally no. |
| Shareholder taxation | C-Corp: Taxed on dividends (0/15/20% qualified rate). S-Corp: Taxed on pass-through income at individual rates (up to 37%). |
| Double taxation | C-Corp: Yes, profits taxed at corp level and again at shareholder level. S-Corp: No, single level of tax at shareholder level. |
| Number of shareholders | C-Corp: Unlimited. S-Corp: Maximum 100. |
| Types of shareholders | C-Corp: Any entity or individual, including foreign shareholders. S-Corp: Must be U.S. citizens/residents, certain trusts, no corporations or partnerships. |
| Classes of stock | C-Corp: Multiple classes allowed (common, preferred). S-Corp: Only one class of stock (voting vs. non-voting is permitted, but no economic differences). |
| Fiscal year | C-Corp: Any fiscal year. S-Corp: Must use calendar year unless approved for a business purpose or Section 444 election. |
| Accumulated earnings tax | C-Corp: Yes, 20% on excess accumulation. S-Corp: N/A. |
| Personal holding company tax | C-Corp: Potentially. S-Corp: N/A. |
| Built-in gains tax | C-Corp: N/A. S-Corp: Applies on gains from C-corp assets converted to S-corp status (within 5 years). |
| Self-employment tax on income | C-Corp: No SE tax on dividends; W-2 wages subject to payroll taxes. S-Corp: No SE tax on distributions; W-2 wages subject to payroll taxes. |
| QSBS eligibility (Section 1202) | C-Corp: Yes. S-Corp: No. |
| Healthcare deduction for 2%+ owners | C-Corp: Fully deductible by corp, excluded from employee income. S-Corp: Deductible but must be included in W-2, then deducted on 1040. |
| K-1 issued to shareholders? | C-Corp: No, shareholders receive Form 1099-DIV for dividends. S-Corp: Yes, each shareholder receives Schedule K-1 (Form 1120-S). |
| State tax treatment | C-Corp: Most states recognize federal entity. S-Corp: Some states do not recognize S-corp status and tax at entity level. |
The choice between these is made once and lived with for years, and it is usually made on the first year's tax outcome alone. Model several years, including what happens if you raise money, bring in an owner who is not eligible, or sell. The exit is where the wrong structure costs the most.
Ankit Sarawagi, CPA, CA, MBA · LinkedInWhen C-Corp Makes More Sense
- You plan to seek venture capital or institutional investment (VCs typically require C-corp structure)
- You want to issue multiple classes of stock with different rights (preferred stock for investors)
- You have more than 100 shareholders or want foreign shareholders
- You want to issue QSBS under Section 1202 for major capital gains exclusions
- You plan to retain significant earnings inside the company and reinvest at the lower 21% corporate rate
- The business owner-employees need substantial tax-free fringe benefits
- You are planning an IPO (public companies are typically C-corps)
When S-Corp Makes More Sense
- You want to avoid double taxation and will distribute most profits
- You have 100 or fewer U.S. citizen/resident shareholders
- You want to reduce self-employment tax on pass-through income (by splitting income between W-2 wages and distributions)
- Your business is not planning to take institutional venture capital
- Your state recognizes S-corp status and doesn't impose entity-level tax
- You want losses to flow through to shareholders (particularly valuable in startup years)
Conversion Rules
C-Corp to S-Corp Conversion
File Form 2553 by March 15 of the year in which the election is to be effective (or at any time during the prior tax year). All shareholders must consent. The built-in gains (BIG) tax applies for 5 years on any gain from assets that appreciated before the S election, this is the primary tax cost of conversion.
- Accumulated C-corp earnings and profits (E&P) remain; distributions from E&P are dividends (not tax-free pass-through)
- C-corp losses do not carry through to the S-corp; they are trapped at the entity level
S-Corp to C-Corp Conversion (Revocation)
An S-corp election can be revoked voluntarily (by consent of shareholders holding more than 50% of stock) by filing a statement of revocation with the IRS. The revocation is prospective. There is no equivalent built-in gains issue when going from S to C.
Pro Tip: Conversions can have significant tax consequences. Model out the after-tax impact over 5-10 years before converting. The built-in gains period is 5 years after the S-election effective date, not 5 years after the conversion.
Key Filing Differences: Form 1120 vs Form 1120-S
| Filing Element | Form 1120 (C-Corp) vs Form 1120-S (S-Corp) |
|---|---|
| Due date | Both: April 15 for calendar-year filers (or 15th day of 4th month for fiscal year) |
| Extension form | Both: Form 7004 for 6-month extension |
| Estimated taxes | 1120: Required if expect to owe $500+. 1120-S: Generally no entity-level estimated taxes; shareholders pay estimates individually. |
| K-1s issued | 1120: No K-1s. 1120-S: K-1 to each shareholder. |
| E-file mandate | 1120: Mandatory at $10M+ assets. 1120-S: Similar e-file requirements. |
| Special schedules | 1120: Schedule C (DRD), J, K, L, M-1/M-2/M-3. 1120-S: Schedule K, K-1, L, M-1, M-2. |
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Frequently Asked Questions
Which pays more tax, C-corp or S-corp?
It depends on the distribution policy and owner's marginal rate. If the owner is in the 37% bracket and takes all profit as salary from either structure, the C-corp's retained income is taxed at 21% (favorable); but distributing that retained income triggers a second tax. Model your specific situation.
Can an LLC be taxed as an S-corp?
Yes. An LLC can elect to be treated as a corporation (Form 8832) and then elect S-corp status (Form 2553). This is the common 'S-corp election for LLC' structure used by small businesses.
Does an S-corp pay payroll taxes?
Yes, on the W-2 wages paid to owner-employees. Distributions (above reasonable compensation) are not subject to payroll taxes. This is the S-corp payroll tax savings strategy.
What is reasonable compensation for an S-corp owner?
The IRS requires S-corp owner-employees to pay themselves a reasonable market-rate salary before taking distributions. No bright-line rule exists; compare to what an unrelated employer would pay for the same services.
Can a C-corp own an S-corp?
No. S-corps cannot have corporate shareholders (other than certain qualified Subchapter S subsidiaries). If a C-corp owns stock in an S-corp, the S election is automatically terminated.
Written by
Ankit Sarawagi, CPA, CA, MBA
Ankit leads the finance team at Profitjets, where he has worked with 500+ businesses across the US on bookkeeping, tax and CFO-level strategy. He writes about the habits that keep small business books accurate all year. Connect on LinkedIn
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