Entity Tax Preparation: S-Corp, C-Corp, Partnership, and LLC Returns

File your S-corp return three months late with five shareholders and you owe $3,525 in IRS penalties before the examiner has looked at a single line item. Fail to pay yourself a reasonable salary from your S-corp, and the IRS reclassifies your distributions as wages, triggering back payroll taxes plus penalties and interest that can easily exceed what you saved. Skip the California LLC fee on a year with $600,000 in gross revenue and the FTB adds a $2,500 assessment to your next audit. Entity tax compliance is not where most small business owners want to discover these rules. Silicon Valley Tax prepares business entity returns for S corporations, C corporations, partnerships, and LLCs throughout the Bay Area, with the same planning discipline on entity returns that we apply to individual returns.

Our office is at 2051 Junction Ave, San Jose CA 95131. We work with businesses in San Jose, Santa Clara, Sunnyvale, Cupertino, Mountain View, and across Silicon Valley and the broader Bay Area. Reach us at (408) 383-9870 or book a free consultation online.

Entity Types and the Returns They File

Every business entity structure creates a different federal and California filing obligation. The wrong structure for your situation costs money every year in taxes that do not need to be paid. The right structure, maintained correctly, keeps the tax burden at its legal minimum while giving you the liability protection and ownership flexibility the business needs.

S Corporation (Form 1120S)

An S corporation is a pass-through entity for federal income tax purposes. The corporation itself does not pay federal income tax at the entity level. Instead, income, deductions, credits, and losses flow through to each shareholder on Schedule K-1 in proportion to their ownership percentage. Each shareholder reports their K-1 items on their individual Form 1040, paying tax at their individual rate.

The S-corp election (Form 2553) is attractive for profitable small businesses because it eliminates the double taxation of C-corp dividends and can reduce self-employment taxes relative to a sole proprietorship or partnership structure. However, the S-corp election comes with strict rules: only one class of stock allowed, no more than 100 shareholders, shareholders must be U.S. individuals (not corporations or nonresident aliens), and the corporation must use a calendar year unless it can demonstrate a valid business purpose for a fiscal year.

California does not follow federal pass-through treatment entirely. California taxes S-corps at 1.5% of net income (minimum $800) in addition to taxing each shareholder on their K-1 income. The California S-corp return is Form 100S. The combined federal pass-through treatment plus California entity-level tax is still significantly better than C-corp double taxation for most Bay Area small businesses, but it is not a free pass.

The Form 1120S must be filed by March 15 for calendar-year corporations, or September 15 if an extension (Form 7004) is filed. K-1s must be provided to shareholders by March 15 so they can include the information on their individual returns due April 15.

C Corporation (Form 1120)

A C corporation is a separate taxable entity subject to corporate income tax at the federal flat rate of 21% on all taxable income. After paying corporate tax, remaining after-tax profits can be retained in the corporation or distributed as dividends. Shareholders pay tax on dividends at preferential qualified dividend rates up to 23.8% federal. In California, dividends are taxed as ordinary income at rates up to 13.3%. The combined effective rate on a dollar of C-corp profit that is earned and then distributed can approach 60% in California, which is why most small profitable businesses prefer S-corp or partnership structures.

C-corps are the appropriate structure in specific circumstances. Venture capital investors generally require C-corp status because they cannot hold pass-through entity interests in their fund vehicles, and because the qualified small business stock (QSBS) exclusion under IRC Section 1202 applies only to C-corp stock. A C-corp that qualifies for QSBS treatment allows early investors and founders to exclude up to $10 million (or 10 times their basis) in capital gains from federal tax entirely. That potential exclusion is worth more to most VC-backed founders than the pass-through savings of an S-corp would be. See our QSBS Section 1202 page for the qualification rules and planning checklist.

The Form 1120 is due April 15 for calendar-year C-corps, with a 6-month extension available (Form 7004) pushing the deadline to October 15. California follows the same federal deadline structure for Form 100.

Partnership (Form 1065)

A partnership is a pass-through entity with two or more partners. The partnership files an informational return (Form 1065) that reports total income, deductions, and credits, then allocates those items to each partner on a Schedule K-1. Partners are taxed on their distributive share of partnership income regardless of whether they actually received a cash distribution. This creates a potential cash flow mismatch where a partner owes tax on income the partnership has not distributed, which is particularly common in real estate partnerships and investment funds that retain capital for reinvestment.

Partnership tax is technically more flexible than S-corp tax because partnership agreements can allocate items of income, loss, deduction, and credit disproportionately to ownership percentage, as long as the allocations have substantial economic effect under the Treasury regulations under IRC Section 704. This flexibility is one reason venture capital funds and private equity funds are structured as limited partnerships. General partners receive a carried interest entitlement that is a disproportionate profit allocation, not compensation in the traditional sense, and is structured carefully to achieve capital gain treatment at the fund level.

California partnership returns are filed on Form 565. Multi-member LLCs taxed as partnerships use Form 568. The California due dates follow the federal calendar: March 15 for calendar-year partnerships, September 15 with extension.

LLC: Choosing the Right Tax Classification

An LLC is a state-law entity that provides liability protection. For federal tax purposes, an LLC is a disregarded entity (single-member), a partnership (multi-member), or a corporation (if an election is made). The choice of federal tax classification is separate from the state law classification and is made on Form 8832 (for corporate elections) or Form 2553 (for S-corp election). A single-member LLC with no election is taxed as a sole proprietorship, with all activity reported on the owner's Schedule C. A multi-member LLC with no election is taxed as a partnership. A multi-member LLC that has made an S-corp election is taxed as an S-corp for federal purposes.

California imposes the $800 annual minimum franchise tax on all LLCs regardless of income or activity, and an additional LLC fee based on total California-source gross receipts (not net income). The LLC fee can be substantial for high-revenue businesses even when the business is not profitable, which is an important planning consideration for businesses with high gross revenue but thin margins.

K-1 Preparation and the Reporting Chain

Schedule K-1 is the document that connects an entity return to its owners' individual returns. Every partner in a partnership, every shareholder in an S-corp, and every beneficiary of a trust or estate receives a K-1 reporting their allocated share of the entity's income, deductions, credits, and other items. The K-1 must be prepared accurately and delivered on time, or the downstream individual returns cannot be filed correctly.

The K-1 for a partnership or S-corp includes not just ordinary income or loss but also separately stated items that each owner must track: Section 179 deductions, charitable contributions, investment interest, foreign taxes, Section 1231 gains and losses, Section 1061 long-term capital gain information for fund interests, and many others. Owners with interests in multiple pass-through entities can receive a stack of K-1s from different partnerships, S-corps, and trusts, all of which must be reconciled and reported on their individual returns.

Late K-1s are one of the most common reasons individual returns are extended. Partnerships and S-corps have a March 15 due date for a reason: to give shareholders and partners time to file their April 15 individual returns. When a partnership extends to September 15, the partners' individual returns must also be extended. We track all K-1 expectations for our clients and coordinate the entity and individual filing calendars together, not as separate engagements.

Reasonable Compensation: The S-Corp Owner's Landmine

The most audited issue on S-corp returns involving active owner-employees is reasonable compensation. The IRS's position is clear: if a shareholder works in the business and receives distributions, they must also receive a salary that represents fair market compensation for the services they perform. Salary is subject to payroll taxes (FICA: 15.3% on wages up to the Social Security wage base, 2.9% above). Distributions are not. An S-corp owner who takes $200,000 in distributions and zero salary saves approximately $7,650 in payroll tax compared to taking $50,000 salary and $150,000 in distributions, using 2025 figures. The IRS notices the pattern because the zero-salary return is a statistical outlier.

The determination of what is reasonable requires analysis of the specific role, comparable market compensation, the size and profitability of the business, geographic market rates, and the amount of time the owner devotes to the business. We document the reasonable compensation determination in a memo for every S-corp client that takes distributions, using industry compensation survey data as a reference point. Bay Area reasonable compensation determinations are particularly important because market wages in Silicon Valley are high, and a compensation figure that would be reasonable in another market may be understated relative to what a comparable Bay Area employee would earn.

Quarterly Estimated Taxes for Business Owners

S-corp and partnership owners do not have an employer withholding taxes on their K-1 income. The entire tax liability on pass-through income is the owner's individual responsibility, paid through quarterly estimated tax payments. Missing the quarterly deadlines or underpaying results in the same underpayment penalty that applies to individuals under IRC Section 6654, computed quarterly. For a Bay Area business owner with $500,000 of K-1 income and a combined federal and California effective rate of 45%, the annual tax liability on that income is approximately $225,000, requiring four quarterly payments of roughly $56,000 each. Getting this projection wrong in the first quarter is expensive because interest accrues from the first deadline regardless of what you pay later.

We build estimated tax projections for all entity clients and issue payment reminders with amounts tied to the current-year income projection, updated quarterly as actual figures become available. The prior-year safe harbor under IRC Section 6654(d)(1)(B) is available to business owners with AGI over $150,000, requiring payments equal to 110% of the prior year's tax liability. This can be a useful backstop in years when income is difficult to project accurately.

Multi-State Apportionment for Bay Area Businesses

A Bay Area business that sells products or services to customers in other states, employs remote workers in other states, or operates locations in other states is likely to have tax nexus and filing obligations in those states. Multi-state business tax compliance requires determining where the business has nexus, completing income apportionment calculations for each nexus state, and filing returns in those states.

California uses a single-sales-factor apportionment formula for most businesses. The percentage of total sales made to California customers determines the fraction of the business's income subject to California tax. Other states use different formulas. A California SaaS company with 60% of its customers in California and significant revenue in New York, Texas, and Washington may owe tax in California (high income, 21%+ effective state rate), New York (8.85% corporate rate, or up to 10.9% for large corporations), and potentially other states depending on their nexus rules.

Economic nexus thresholds, established following the Supreme Court's 2018 South Dakota v. Wayfair decision, have extended to income taxes in many states. A business does not need a physical presence to create income tax nexus in states that have adopted economic nexus standards. For Bay Area tech companies with national or international customer bases, we conduct a nexus study at the start of the engagement to identify all states where filings are required, estimate the total multi-state tax liability, and structure compliance to avoid surprises.

California Franchise Tax and Annual Statement of Information

California entities have two annual compliance obligations beyond the income tax return: the franchise tax and the Statement of Information. The California franchise tax minimum of $800 is due the 15th day of the 4th month of the entity's tax year (April 15 for calendar-year entities). New LLCs and corporations have a first-year exemption from the $800 minimum in some cases, but the rules are specific and have changed over time. Failure to pay the minimum franchise tax results in suspension of the entity's powers, which can void contracts, prevent the entity from defending lawsuits, and eventually result in administrative dissolution.

The Statement of Information (SI-100 for corporations, LLC-12 for LLCs) is filed with the California Secretary of State annually (or biennially for some LLCs) and reports the entity's principal office address, officer and director names and addresses, and registered agent. The filing fee is $25 and the penalty for failure to file is $250. While $250 is not a substantial amount, the underlying issue is that delinquency in Statement of Information filings can result in suspension, with the same consequences as franchise tax suspension.

Documents Needed for Entity Tax Preparation

Entity tax preparation requires a complete and reconciled set of financial records for the year. The foundation is the general ledger or trial balance that ties to the entity's bank and credit card statements. Common documents we need include:

• Trial balance or compiled financial statements for the tax year
• Prior-year entity return (if you are a new client or switching preparers)
• Payroll reports: W-3 summary, 941 quarterly payroll tax returns, and W-2s issued to employees
• 1099s issued to contractors (1099-NEC) and received from payers (1099-K, 1099-INT, 1099-DIV)
• Shareholder/partner equity rollforward showing beginning balances, contributions, distributions, and income allocations
• Loan agreements for any shareholder loans or loans from the entity to shareholders
• Depreciation schedule from the prior year (or a complete asset list if starting fresh)
• Records of fixed asset purchases and disposals during the year
• Home office documentation if any owner claims a home office deduction
• Vehicle logs if the entity or owner deducts vehicle expenses
• State tax notices or correspondence received during the year

Contact Information

Silicon Valley Tax
2051 Junction Ave, Suite 200
San Jose, CA 95131
Phone: (408) 383-9870
Email: admin@siliconvalleytax.co
Hours: Mon-Fri 8am-8pm, Sat-Sun 8am-6pm

Frequently Asked Questions

What is the difference between an S-corp and a C-corp for tax purposes, and which is better for my Bay Area business?

A C corporation pays corporate income tax at 21% federally and distributes after-tax profits as dividends, creating double taxation. An S corporation is a pass-through entity with no federal entity-level tax; income flows to shareholders on K-1. California taxes S-corps at 1.5% of net income (minimum $800) in addition to shareholder-level K-1 tax. For most small profitable Bay Area businesses, the S-corp avoids double taxation. C-corps make sense when seeking venture capital funding, pursuing QSBS exclusion under IRC Section 1202, or retaining earnings at the lower corporate rate. The choice has long-term consequences that are difficult to reverse without tax cost.

What is reasonable compensation for an S-corp owner-employee, and why does it matter?

S-corp shareholders who work in the business must pay themselves a reasonable salary subject to payroll taxes. The IRS scrutinizes S-corps where shareholders take little salary and large distributions, because distributions avoid FICA taxes. Recharacterization of distributions as wages triggers back employment taxes plus penalties. Reasonable compensation is determined by industry, geographic market, services performed, and time devoted. Bay Area determinations require Silicon Valley market wage data. We document the analysis in a memo for every S-corp client taking distributions.

Does my LLC need to file a tax return in California, and what taxes does an LLC owe?

California LLCs owe the $800 annual franchise tax minimum regardless of income. LLCs with California gross income above $250,000 also owe additional LLC fees up to $11,790 per year. For federal purposes, a single-member LLC is disregarded and reports on the owner's Schedule C. A multi-member LLC files Form 1065 (partnership return) federally and Form 568 in California, with K-1s issued to each member. An LLC can elect S-corp or C-corp taxation by filing the appropriate election form.

What is multi-state apportionment and when does my California business owe taxes in another state?

A California business with employees, property, or sales in other states may have tax nexus in those states following South Dakota v. Wayfair and subsequent state economic nexus rules. Once nexus is established, income is apportioned between California and the other state. California uses a single-sales-factor formula. Other states use different formulas. Bay Area SaaS companies with remote employees or nationwide customer bases commonly trigger multi-state obligations discovered only when a state nexus questionnaire arrives. We conduct a nexus study at engagement start to identify all required filings.

When is the tax return due for my partnership or S-corp, and what happens if we file late?

Partnership (Form 1065) and S-corp (Form 1120S) returns are due March 15, one month before the individual deadline, so K-1s can reach owners before April 15. Extensions push the deadline to September 15. Late filing penalties under IRC Sections 6698 and 6699 are $235 per partner or shareholder per month, up to 12 months. Five shareholders, three months late equals $3,525 in penalties before any tax examination. California imposes separate penalties. We file extensions automatically for any entity whose books are not reconciled by early February.

Why Work With Silicon Valley Tax for Entity Returns

Entity tax returns are preparation work and planning work at the same time. The choices made in preparing the return: how compensation is classified, how depreciation is calculated, how multi-state income is apportioned, whether the entity election still makes sense given the business's current stage, all have dollar consequences that compound over years. A return filed by someone who treats entity tax as a compliance task rather than a planning opportunity is a return that costs the owner money.

We prepare S-corp, C-corp, partnership, and LLC returns as part of an integrated engagement with each business owner's individual return. The entity return and the individual return are not separate projects; they are two outputs of one analysis. When we see a planning opportunity on the entity side that affects the individual side, we address it in the same conversation. When we see a risk area, we document it. When we see a deduction that is supported and correctly categorized, we take it.

Serving business entity clients throughout San Jose, Santa Clara, Sunnyvale, Cupertino, Mountain View, Milpitas, Fremont, and the broader Bay Area. Related service pages: individual tax preparation, tax planning and strategy, and CFO and advisory services. Related topics: QSBS Section 1202 and equity compensation tax for founders and early employees.

Entity Nexus Studies and Registered Agent Requirements

California requires every corporation and LLC doing business in the state to maintain a registered agent for service of process and to keep that registration current with the Secretary of State. If you move or change your registered agent and fail to update the filing, legal notices can be missed, which in worst-case scenarios means a default judgment against the entity. Similarly, if you expand into other states, each state where you have nexus requires its own qualification and registered agent. We coordinate the multi-state compliance calendar alongside the multi-state tax filing calendar, so the entity stays in good standing in every state where it operates.

A Note on Combined Entity and Individual Engagements

The most consequential entity tax decisions do not live in isolation on the entity return. They connect directly to the owner's individual return, estimated tax position, and long-term wealth plan. The S-corp owner who takes a $40,000 reasonable salary and $200,000 in distributions saves payroll tax on the distribution amount, but the documentation supporting that salary needs to be in place before the IRS asks. The partner in a real estate LLC who has suspended passive losses from prior years needs to understand the disposition rules that allow those losses to be released. The C-corp founder who plans to sell the business in three years needs to know whether their shares will qualify for QSBS exclusion at the time of sale and what steps need to be taken now to protect that eligibility.

When you engage Silicon Valley Tax for your entity return, we treat the entity and the owner as one financial unit. The entity return, the owner's individual return, and the quarterly estimated tax calculations are planned together, not filed separately by different preparers who never compare notes. That integrated approach is how planning opportunities get identified rather than overlooked, and how compliance risks get caught before the IRS or FTB finds them first. If you are currently working with a preparer who handles your entity return but refers you elsewhere for your individual return, or vice versa, a conversation with us about consolidating that work may be worth having.