The choice between S-Corp and C-Corp changes a company's federal tax bill by five to seven figures over a normal business life. This is the CPA-level comparison that goes beyond 'avoid double taxation' and looks at rates, distributions, payroll discipline, QBI, QSBS, and the specific fact patterns where each structure wins.
Headline Tax Rates: The Start, Not the End, of the Analysis
The federal C-Corp rate has been a flat 21% since the Tax Cuts and Jobs Act of 2017. Add state tax (ranging from 0% in Nevada to nearly 12% in New Jersey and California) and the all-in corporate rate sits between 21% and 30% for most businesses.
S-Corp income flows through to shareholders at individual rates, which top out at 37% federal plus state. On the surface the C-Corp rate looks lower. Two factors invert that. First, S-Corp owners can claim the Section 199A Qualified Business Income (QBI) deduction of up to 20% of qualified pass-through income, bringing the effective federal rate down to roughly 29.6%. Second, C-Corp income taxed at 21% is taxed again when distributed as dividends (20% plus 3.8% NII for most owners), producing a blended rate above 36% when earnings are taken out.
Distribution Strategy: Where the Real Money Is
S-Corp distributions are generally tax-free to the extent of basis. An owner who draws $300,000 in distributions above a reasonable $100,000 W-2 salary pays income tax on the full $400,000 of pass-through income, but the actual distribution moving from corporate account to personal account is not a separate taxable event.
C-Corp distributions are dividends. The corporation pays 21% federal tax on earnings, and the shareholder pays 20% on the qualified dividend (plus 3.8% NII). The double layer means C-Corp retained earnings are much more efficient than C-Corp distributed earnings. This is why C-Corps that never distribute (reinvesting in growth) look very different on paper than C-Corps that pay dividends every year.
Payroll Discipline: The S-Corp Reasonable Compensation Rule
The IRS treats S-Corp owner-employees as employees first. They must receive reasonable W-2 compensation before distributions are taken. Reasonable is defined by comparable market pay for the role, the owner's duties, and the company's ability to pay. The S-Corp audit risk is concentrated here: owners who take $0 salary and $500,000 in distributions are the fastest path to reclassification.
We document reasonable compensation annually using comparable studies (RCReports, BLS data, industry benchmarks) and put the analysis in the file. If the IRS audits the payroll and finds the documentation, the conversation ends much faster.
QSBS: The C-Corp Exit Benefit That Changes the Math
Section 1202 Qualified Small Business Stock can exclude up to the greater of $10 million or 10x basis of gain on sale of qualifying C-Corp stock held more than five years. For founders and early employees, QSBS can mean a federal tax rate of 0% on the first $10 million of exit proceeds per shareholder.
S-Corps cannot issue QSBS. This single provision often decides the structure for high-growth companies heading toward a meaningful exit. A $30 million exit with four QSBS-qualifying founders can save $20 million or more in federal tax compared to an S-Corp pass-through sale of the same business.
Benefits, Fringes, and Owner Medical
C-Corps can deduct the full cost of owner-employee benefits including medical, dental, disability, and Section 105 medical reimbursement. S-Corps treat benefits to 2%+ shareholders as additional wages, eliminating most of the tax advantage.
For closely held businesses with high medical expenses or robust benefit programs, the C-Corp benefit deduction can be worth more than the double-tax cost, especially at lower profit levels.
QBI Deduction Mechanics for S-Corp Owners
Section 199A gives S-Corp owners a deduction of up to 20% of qualified business income, subject to wage and investment limits for high earners. Specified Service Trade or Business (SSTB) rules phase out the deduction for professionals (law, accounting, consulting, health) above certain income thresholds.
Planning around QBI involves adjusting reasonable compensation (wages count in the wage limit but reduce QBI), structuring related activities correctly, and monitoring taxable income against the threshold. For the right business, QBI is worth 3 to 4 percentage points of effective rate.
When Each Structure Wins
S-Corp wins when the business is stable, profitable, distributes most earnings annually, has only U.S. individual shareholders, and is not on a venture-scale trajectory. The QBI deduction and single-layer taxation make it the most tax-efficient structure for most profitable service businesses under $5 million in earnings.
C-Corp wins when the business plans to raise venture capital (investors need a C-Corp), retain earnings for growth, issue stock options broadly, or target a QSBS-qualifying exit. It is also the only structure available when shareholders include foreign owners, corporations, or trusts that disqualify S election.
Switching Structures: Harder Than It Sounds
Converting a C-Corp to an S-Corp triggers a five-year built-in gains tax period and can strip QSBS eligibility. Converting an S-Corp to a C-Corp is simpler but can leave AAA (accumulated adjustments account) questions for subsequent distributions. Neither direction is free, and the wrong conversion can cost more than the tax it was trying to save.
We model the conversion cost, including built-in gains, AAA mechanics, basis reset, and loss of QBI or QSBS. Where the math works, we execute the conversion with payroll, documentation, and shareholder consents aligned.
State Tax Differences That Influence the Decision
State taxation of S-Corps and C-Corps varies. California, for example, imposes a 1.5% S-Corp tax (8.84% C-Corp rate). New York City has separate corporation tax rules that do not always recognize S-Corp status. Tennessee and a few other states impose franchise or excise tax regardless of federal classification.
Modeling the structure should always include the state(s) where the business operates. A federally optimal S-Corp can become an after-state wash, and a high-tax state may push a profitable closely held business toward different planning.
Practical Steps to Make the Choice This Quarter
Step 1: Pull last twelve months of financials and projected next twelve months. Step 2: Identify owners by jurisdiction and equity structure. Step 3: Define expected exit (sale, IPO, hold). Step 4: Model S-Corp and C-Corp federal and state taxes side by side. Step 5: Decide and file the election (Form 2553 for S, no election needed for default C).
For most growing businesses, the analysis takes 90 minutes with a CPA. The savings often run six figures over the planning horizon.
Can a C-Corp elect S-Corp status?
Yes, through Form 2553. The five-year built-in gains tax and other rules can make the switch expensive. Model before electing.
Can an S-Corp have foreign shareholders?
No. A single non-resident alien shareholder terminates the S election. Foreign-owned pass-throughs must be LLCs taxed as partnerships or C-Corps.
Which is better for a SaaS startup?
Almost always a C-Corp, because venture investors require it and QSBS is a meaningful exit benefit.
Do both S-Corps and C-Corps file 1099s and handle payroll the same way?
Information return obligations are similar. Payroll is mandatory for S-Corp owner-employees but optional for C-Corp shareholders not also serving as employees.