C-Corp vs S-Corp vs LLC: The Complete Entity Selection Guide for CPAs

Most clients should default to LLC — with S-Corp election once net profit reliably exceeds $60,000–$70,000. C-Corp is the right answer in a narrow but important set of circumstances: businesses actively seeking venture capital or private equity investment, operations with foreign shareholders, owners planning an IRC §1202 QSBS-eligible exit, and companies that will retain substantial earnings internally rather than distributing them. The entity choice is not permanent — restructuring is possible — but the tax cost of converting in the wrong direction is real, and getting the initial structure right avoids those costs entirely. Here is how to run the analysis systematically.

How Each Structure Is Taxed

LLC (default pass-through): A single-member LLC taxed as a disregarded entity reports on Schedule C; a multi-member LLC taxed as a partnership files Form 1065 with K-1 allocations to partners. In both cases, all net income passes through to the owner's Form 1040 and is subject to both federal income tax and self-employment tax — 15.3% on the first $176,100 in net earnings (Social Security + Medicare) and 2.9% above that ceiling under IRC §1401.

S-Corp: An LLC or corporation that has elected S-Corp treatment under IRC §1361 maintains pass-through taxation with a critical split: the owner-employee receives a W-2 salary subject to FICA, while the remaining profit distributes free of payroll tax. Income flowing through the K-1 qualifies for the 20% Section 199A deduction under OBBBA — reducing the effective top marginal rate from 37% to 29.6%.

C-Corp: A regular corporation taxed at the entity level under Subchapter C pays a flat 21% federal corporate rate on net income (Tax Cuts and Jobs Act, Pub. L. 115-97, §13001). After-tax earnings distributed to shareholders as qualified dividends are taxed again at 0%, 15%, or 20% — plus the 3.8% Net Investment Income Tax for high-income shareholders under IRC §1411 — under IRC §1(h). This "double taxation" is what drives most profitable small businesses toward pass-through structures, but the retained earnings calculus can make C-Corp advantageous when profits are reinvested rather than distributed. Accounting method note: C-corporations with average annual gross receipts exceeding $31 million (the 2025 indexed threshold under IRC §448) must use the accrual method of accounting. For the mandatory change procedures, §481(a) adjustment spread rules, and how to time a voluntary switch to minimize tax cost, see Switching from Cash Basis to Accrual Accounting: Tax Implications Every CPA Must Know.

QBI Deduction: The Pass-Through Advantage C-Corp Forfeits

The Section 199A Qualified Business Income deduction — made permanent by the One Big Beautiful Bill Act (OBBBA) in 2025 — allows pass-through owners to deduct up to 20% of net business income, reducing the effective top marginal rate from 37% to 29.6% (IRC §199A). C-Corp shareholders are categorically ineligible: dividends paid from after-tax C-Corp earnings are not QBI and generate no Section 199A deduction.

At $500,000 in pass-through net income, the QBI deduction produces up to $100,000 in deductions — worth $37,000 in federal tax savings at the top bracket. A high-income client who distributes C-Corp profits as dividends forfeits this entirely. For clients near or above the Section 199A income thresholds ($197,300 single / $394,600 MFJ in 2025), the W-2 wage limitation and SSTB rules add complexity — but the deduction remains available for non-SSTB pass-throughs even at high income levels. For the full methodology, see QBI Deduction in 2025: How Section 199A Works After OBBBA.

SSTB professionals — physicians, attorneys, accountants, financial advisors — who are above the upper phase-out threshold ($247,300 single / $494,600 MFJ) receive a zero §199A deduction regardless of entity structure. For these clients, the QBI forfeiture cost of C-Corp is lower, and the 21% retained earnings rate becomes more competitive. Model the individual facts before assuming S-Corp is automatically superior for high-income SSTB owners.

Retained Earnings: Where C-Corp Has a Real Advantage

For businesses that reinvest substantially all earnings rather than distributing them, C-Corp's 21% rate on retained earnings creates a genuine tax deferral advantage that can compound significantly over time.

The mechanics: an S-Corp or LLC with $1,000,000 in net income generates a K-1 that flows to the shareholder's Form 1040 in full — taxes are owed at up to 37% (or 29.6% after QBI) whether or not cash is actually distributed. A C-Corp with $1,000,000 in net income pays 21% at the entity level and retains the remaining $790,000 for reinvestment, with no additional shareholder-level tax until dividends are declared or shares are sold. For a business compounding retained earnings over five to ten years before a liquidity event, this deferral creates real value.

The accumulated earnings tax: IRC §531 imposes a 20% penalty tax on C-Corps that accumulate earnings beyond "reasonable business needs" for the purpose of avoiding shareholder-level dividend taxation. Courts and the IRS examine whether accumulations are tied to documented business purposes — expansion plans, debt retirement, equipment acquisition. Maintain written board resolutions authorizing each year's retained earnings strategy and the specific business purpose they serve. The risk is most acute for passive investment holding companies without documented operational plans. Key person life insurance policies held by the corporation are another retention item requiring documented business purpose — the cash value growth inside permanent policies is tax-deferred, but the retention must be tied to a clear continuity planning rationale to withstand accumulated earnings scrutiny. See Key Person Insurance: Premium Deductibility, Death Benefit Tax Treatment, and How to Structure Coverage for how C-Corps document these policies. For the complete AET methodology — the Bardahl working capital formula, the accumulated earnings credit, consent dividends, and year-end documentation checklist — see Accumulated Earnings Tax: How to Help C-Corp Clients Avoid the IRC §531 Penalty.

The practical calculus: For growth companies that will reinvest substantially all profits for five or more years and exit through an acquisition or IPO, C-Corp retained earnings at 21% is legitimate, defensible tax planning. For businesses that distribute most profits to fund owner living expenses, C-Corp creates higher total tax than S-Corp on an after-distribution basis — the combined 21% corporate plus 15–23.8% dividend tax routinely reaches 39–44%.

QSBS: The C-Corp-Only Gain Exclusion

Under IRC §1202, shareholders of Qualified Small Business Stock may exclude up to $10,000,000 in capital gain — or 10 times the adjusted basis of stock sold, if greater — from a C-Corp share sale when the stock has been held for more than five years. The One Big Beautiful Bill Act may have expanded QSBS provisions; consult the enacted statutory text and subsequent IRS guidance for current exclusion limits applicable to shares issued after the effective date. For the complete qualification methodology — C-Corp entity requirements, the gross assets test at issuance, active business documentation, the five-year holding period, state conformity analysis, and the §1045 rollover option — see QSBS Guide 2025: How to Qualify for the IRC §1202 Gain Exclusion Under OBBBA.

Core eligibility requirements:

• The issuing corporation must be a domestic C-Corp — S-Corps, LLCs, and partnerships are categorically ineligible for §1202
• Aggregate gross assets must not exceed $50 million at the time of issuance (and immediately after the issuance per IRC §1202(d))
• Stock must be original-issue stock acquired at initial issuance, not purchased on a secondary market
• The shareholder must hold stock for more than five years (gain may be rolled under §1045 into a replacement QSBS investment to preserve eligibility)
• The corporation must operate an active qualified business — financial services, law, health, accounting, consulting, and certain other §199A-designated SSTBs are explicitly excluded under IRC §1202(e)(3)

For clients whose business is likely to be sold for substantial value and who operate in a qualifying industry, the §1202 exclusion can shelter millions in gain from federal tax entirely. The planning window is narrow — the five-year hold and original-issuance requirement mean QSBS eligibility must be established at or near formation. There is no reliable mechanism to retroactively qualify an existing LLC or S-Corp after the fact; converting to C-Corp restarts the five-year clock from the conversion date.

Ownership and Investment Flexibility

S-Corp restrictions (IRC §1361):

• Maximum 100 shareholders
• Shareholders must be U.S. citizens or permanent residents — no foreign nationals, no foreign entities
• Only one class of stock is permitted (voting and non-voting shares with identical economic rights are allowed; preferred stock is not)
• No corporate or partnership shareholders except in limited Qualified Subchapter S Subsidiary (QSub) structures
• Trusts as shareholders require ESBT or QSST qualification

The moment a client receives a VC term sheet requiring preferred equity, adds a foreign co-founder, or expects more than 100 investors, S-Corp is structurally unavailable. Building an investor-grade cap table requires converting out of S-Corp — at a potential tax cost. For a step-by-step walkthrough of how to navigate this conversation with clients, including timing the conversion to minimize built-in gains exposure, see Advising Clients Who Want to Bring On Investors.

C-Corp advantages for investment:

• Standard equity structure for venture-backed companies: preferred stock with anti-dilution provisions, liquidation preferences, and participating features
• §1202 QSBS eligibility for founders and early investors
• 83(b) election flexibility for restricted stock grants to employees
• Delaware C-Corp is the institutional default for startup formation

LLC advantages:

• Unlimited members, including foreign nationals and foreign entities
• Multiple classes of membership interest for flexibility
• Profits interests — equity compensation that vests into future appreciation with no upfront taxable event for the recipient — are well-established for LLC operating agreements and have no direct S-Corp or C-Corp equivalent (see how profits interests work when adding a new LLC member)

Full Side-by-Side Comparison

When to Choose C-Corp

Recommend C-Corp formation or conversion when:

• The client is raising institutional capital. VC and PE investors require preferred stock structures incompatible with S-Corp's one-class restriction. Form as a Delaware C-Corp when any capital raise is anticipated, even at the planning stage.
• The business has or will have foreign shareholders. S-Corp is categorically unavailable; C-Corp is the investor-grade option.
• The client expects a high-value exit and qualifies for §1202 QSBS. Excluding up to $10 million in gain — at zero federal tax — is a compelling incentive for qualifying businesses to maintain C-Corp status from inception.
• The business will retain substantially all profits for five or more years. Compounding internally at a 21% rate rather than distributing and paying 37% individual rate preserves more capital for growth. Model the breakeven against the QBI deduction forgone.
• The owner is in an SSTB above the §199A upper threshold. Without the QBI deduction, the cost of C-Corp's double taxation shrinks, and retained earnings accumulation becomes more competitive.

When to Choose S-Corp

Recommend S-Corp election when:

• Net profit consistently exceeds $70,000–$80,000 and the client has no plans for outside investment. The SE tax savings — typically $7,000–$22,000+ annually — compound over time. See S-Corp vs LLC: Which Tax Structure Saves More in 2025? for the full breakeven model, state-level analysis, and side-by-side FICA calculations.
• The client is a stable, profitable service business with all-U.S. shareholders. Medical practices, accounting firms, consulting businesses, and financial advisory firms often fit this profile exactly.
• QBI deduction preservation is a priority. The effective 29.6% rate on S-Corp K-1 income is significantly lower than C-Corp's combined tax cost on distributions for most income levels.
• The client wants to maximize Solo 401(k) contributions. S-Corp W-2 wages serve as the compensation base for employee deferral contributions (up to $23,500 in 2025 plus catch-up).

For the reasonable salary determination methodology — BLS OEWS data lookup, the distribution-to-salary ratio test, and board minute documentation requirements — see How to Calculate and Document a Reasonable S-Corp Salary.

When to Choose LLC (Default Pass-Through)

Recommend LLC default taxation — without S-Corp election — when:

• Net profit is below $60,000–$70,000. SE tax savings don't offset payroll and entity return costs at this income level. Simplicity wins.
• The client needs maximum ownership flexibility. Foreign partners, preferred equity investors, or profits-interest recipients are easiest in an LLC structure without the S-Corp restrictions.
• The business is early-stage with variable income. Payroll obligations create cash flow friction when income fluctuates. Defer S-Corp election until income stabilizes.
• California clients with net income in the $60,000–$120,000 range. The 1.5% franchise tax plus $800 minimum franchise fee frequently erases the federal advantage — always model state taxes before advising.
• The client wants to issue profits interests to key employees. LLC profits interests are a well-established form of equity compensation with no upfront taxable event and no direct equivalent in S-Corp or C-Corp structures.

Bottom Line

For the typical small-business CPA client — profitable, self-funded, stable income, U.S. owners — S-Corp election is the correct structure once net profit exceeds $70,000. Below that threshold, LLC default is simpler and cheaper. C-Corp is the right answer when outside investors, foreign owners, QSBS planning, or retained earnings accumulation make its unique features genuinely valuable — and those circumstances are more common in early-stage and high-growth businesses than in established professional practices. The analysis requires knowing the client's five-year outlook: income trajectory, ownership plans, capital needs, and exit strategy. For co-owned businesses, exit planning also means defining how ownership transfers when a partner leaves — at death, disability, or voluntary departure. A properly funded buy-sell agreement governs that transfer and its tax consequences; see How to Structure a Buy-Sell Agreement: The Tax and Insurance Components Explained for the full cross-purchase vs. redemption analysis by entity type. Entity structure is one of the few decisions that compounds over a decade — getting it right at formation typically saves more than any single-year tax strategy. For clients with multiple business lines, real estate holdings, or intellectual property that warrant separation from operations, the entity choice also extends to whether a holding company structure — with separate subsidiary entities — serves the client's liability and succession goals. See Holding Company Structures for Business Clients: When and How to Recommend One for the complete evaluation framework. The best time to revisit this analysis for existing clients is year-end, when full-year income is visible and election decisions can be implemented properly. See Year-End Tax Planning Checklist for CPAs for how entity structure analysis fits into the broader planning sequence.

FAQs

Can an LLC convert to a C-Corp if the client later decides to seek venture capital?

Yes, but the conversion has tax consequences that must be modeled before execution. When an LLC (taxed as a partnership or disregarded entity) contributes assets to a newly formed C-Corp, the contribution is generally tax-free under IRC §351 if the contributing owners receive at least 80% of the combined voting power and value immediately after the exchange. However, built-in gains, debt in excess of basis, and recapture items can trigger income recognition. A C-Corp formed from an S-Corp carries a built-in gains tax risk under IRC §1374 for five years after conversion — any gain recognized on assets that existed at conversion is taxed at the 21% corporate rate at the entity level. Structure conversions well before the anticipated exit to avoid recognition events at the worst possible time.

Does C-Corp ever make sense for a profitable professional practice?

Rarely, but model it explicitly for SSTB professionals above the §199A upper threshold. A physician at $600,000 in taxable income receives a zero QBI deduction regardless of entity structure — the QBI forfeiture cost of C-Corp is effectively zero. At that income level, the comparison is 21% corporate rate on retained earnings versus 37% individual rate on pass-through income distributed annually. If the practice retains significant earnings for expansion, C-Corp's 21% rate on retained earnings is genuinely competitive — but only until those earnings are eventually distributed, when shareholder-level dividend tax applies. For practices that distribute most earnings annually, S-Corp's combined FICA-plus-income-tax rate typically remains lower.

What is the built-in gains tax for S-Corp elections on a prior C-Corp?

When a C-Corp converts to S-Corp status — or when a C-Corp makes the S-Corp election — the resulting S-Corp inherits "built-in gain" equal to the excess of fair market value over basis at the conversion date. Under IRC §1374, any built-in gain recognized during the 5-year recognition period following conversion is taxed at the 21% corporate rate at the entity level, in addition to the shareholder's individual income tax on the K-1 income. The built-in gains tax is most significant for C-Corps with appreciated real estate, goodwill, or equipment. Waiting out the 5-year recognition period — or structuring the conversion to minimize FMV-over-basis — is essential planning for any C-Corp-to-S-Corp conversion.

Can an S-Corp have a C-Corp as a shareholder?

No, with a narrow exception. S-Corp shareholders must be individuals, certain trusts, or certain tax-exempt organizations — C-Corps, partnerships, and other S-Corps are ineligible as shareholders. The exception is the Qualified Subchapter S Subsidiary (QSub): an S-Corp can own a 100%-wholly-owned subsidiary S-Corp that elects QSub status, causing the subsidiary to be treated as a disregarded entity of the parent S-Corp for federal tax purposes. For the complete QSub election process — eligibility requirements, Form 8869 filing mechanics, built-in gains analysis, and termination consequences — see How to Make a QSub Election.

How do state taxes change the entity structure analysis?

Significantly, and the variation is large. California imposes an $800 minimum franchise tax plus 1.5% net income franchise tax on S-Corps, which often eliminates the federal SE tax advantage at net income below $120,000. California C-Corps pay 8.84% corporate tax — much higher than the federal 21%. New York City imposes the General Corporation Tax on S-Corps. Tennessee's excise tax applies to S-Corp net income. States with no income tax — Texas, Florida, Nevada, Wyoming, Washington — create a clean environment where the federal analysis drives the decision. Always layer in the specific state tax treatment before finalizing any entity structure recommendation.

What happens to the QBI deduction if the client switches from S-Corp to C-Corp mid-year?

A corporation that revokes its S-Corp election during the tax year must allocate income and deductions between the S period (when §199A applies) and the C period (when it does not), on a per-day basis or through a closing of the books if elected. The §199A deduction applies only to income allocable to the S period. Revocation of an S-Corp election during the tax year also triggers the 5-year waiting period before a new S-Corp election can be made — under IRC §1362(g), a corporation that revokes or terminates its S-Corp election generally cannot re-elect S-Corp status for five taxable years without IRS consent.

Arvori helps CPAs model entity structure decisions — comparing S-Corp, C-Corp, and LLC tax outcomes across income scenarios, state tax environments, and QSBS eligibility analyses for their entire client roster. Learn more at arvori.app.