The choice between Form 1120 and Form 1065 comes down to entity type: Form 1120 is the federal income tax return a C corporation files to pay tax on its own profits at a flat 21% rate, while Form 1065 is the information return a partnership or multi-member LLC files to report results that then pass through to the owners’ personal returns. That single split — whether the business pays tax or the owners do — drives nearly every other difference between the two forms.
S corporations file a different return, Form 1120-S, and aren’t part of this comparison.
Who Files Form 1120 and Who Files Form 1065
Form 1120 is required for every domestic C corporation. The corporation uses it to report income, gains, losses, deductions, and credits, then calculates and pays its own federal income tax.1Internal Revenue Service. About Form 1120, U.S. Corporation Income Tax Return
Form 1065 is required for partnerships of every stripe — general partnerships, limited partnerships, and limited liability partnerships. It’s also the default return for any LLC with two or more members that hasn’t elected to be taxed as a corporation.2Internal Revenue Service. About Form 1065, U.S. Return of Partnership Income The partnership files the return, then issues each partner a Schedule K-1 showing that partner’s share of income, deductions, and credits.
A multi-member LLC lands in Form 1065 territory automatically. If the LLC has more than one member and hasn’t filed Form 8832 to elect corporate treatment, the IRS classifies it as a partnership.3Internal Revenue Service. Limited Liability Company – Possible Repercussions
Who Actually Pays the Tax
The most consequential difference between these forms is whether the business itself owes federal income tax.
A C corporation filing Form 1120 is a taxpayer in its own right. It calculates net taxable income, applies any credits, and pays tax directly to the IRS. Under IRC Section 11, that tax is a flat 21% of taxable income, no matter how much or how little the corporation earns.4GovInfo. 26 USC 11 – Tax Imposed
A partnership or multi-member LLC filing Form 1065 pays zero federal income tax at the entity level. Form 1065 is purely an information return. The partnership calculates its net income or loss, allocates the results among the partners according to the partnership agreement, and each partner’s distributive share flows onto their personal return, taxed at the partner’s individual rate.2Internal Revenue Service. About Form 1065, U.S. Return of Partnership Income
One practical consequence catches first-time partnership owners off guard: partners owe tax on their distributive share whether or not the partnership actually distributes cash. If the partnership earns $200,000 and reinvests every dollar, the partners still report $200,000 of income on their personal returns and owe tax on it. That’s phantom income, and it’s real.
The Double Taxation Problem
The 21% corporate rate looks attractive next to a 37% top individual rate, but there’s a catch. When a C corporation distributes after-tax profits to shareholders as dividends, those dividends get taxed a second time on the shareholders’ personal returns.
Qualified dividends are taxed at long-term capital gains rates of 0%, 15%, or 20%, depending on the shareholder’s taxable income.5Internal Revenue Service. Topic No. 404, Dividends and Other Corporate Distributions For 2026, the 20% rate kicks in at taxable income above $545,500 for single filers and $613,700 for married couples filing jointly. High-income shareholders also face the 3.8% net investment income tax on dividends once modified adjusted gross income exceeds $200,000 for single filers or $250,000 for joint filers.6Internal Revenue Service. Topic No. 559, Net Investment Income Tax
In the worst case, a dollar of corporate profit gets hit with 21% at the corporate level, then up to 23.8% when it reaches the shareholder. The combined effective rate approaches 40%. Partnerships avoid this stack entirely because the income is only taxed once.
The Section 199A Deduction
Partners and LLC members have another edge. Section 199A allows owners of pass-through businesses to deduct up to 20% of their qualified business income before calculating personal income tax. A partner with $100,000 of qualified business income could deduct $20,000, paying tax on only $80,000.7Office of the Law Revision Counsel. 26 USC 199A – Qualified Business Income
This deduction was originally set to expire after 2025, but the One Big Beautiful Bill Act, signed into law on July 4, 2025, made it permanent. Above certain income thresholds, the deduction begins to phase down for owners of “specified service” businesses like law firms, medical practices, and consulting firms, and it can be limited based on the wages the business pays or the depreciable property it holds. C corporations get no Section 199A deduction, because corporate income never appears on the owner’s personal return until it’s paid out as a dividend.
How Owners Get Paid
Owner compensation looks very different under the two forms, and the self-employment tax implications are where many people underestimate the cost of pass-through taxation.
C Corporation Owner-Employees
Owners of a C corporation who work in the business receive a W-2 salary like any other employee. The corporation deducts those wages as a business expense, reducing its taxable income. Both the corporation and the owner-employee pay their respective halves of FICA: 7.65% each (6.2% Social Security plus 1.45% Medicare). The owner’s salary is subject to income tax withholding. After paying salaries and other expenses, any remaining profit is taxed at 21%.4GovInfo. 26 USC 11 – Tax Imposed
Partnership and LLC Owners
Partners and LLC members don’t receive W-2 wages for their share of the profits. The partnership reports each owner’s distributive share on a Schedule K-1, and the owner reports that income on Form 1040.2Internal Revenue Service. About Form 1065, U.S. Return of Partnership Income8Internal Revenue Service. Topic No. 554, Self-Employment Tax9Social Security Administration. Contribution and Benefit Base Self-employment income above $200,000 for single filers ($250,000 for joint filers) also triggers a 0.9% Additional Medicare Tax, pushing the Medicare portion to 3.8% on high earnings.10Internal Revenue Service. Topic No. 560, Additional Medicare Tax
Limited partners get a break. Under IRC Section 1402(a)(13), a limited partner’s distributive share of partnership income is excluded from self-employment tax. Guaranteed payments for services are the exception; those are always subject to self-employment tax, even for limited partners.11Internal Revenue Service. Self-Employment Tax and Partners
Guaranteed Payments
Partnerships often pay guaranteed payments to partners who contribute regular services or capital. These payments function somewhat like a salary in that they’re made regardless of whether the partnership turns a profit, and they’re deductible by the partnership on Form 1065. Unlike a W-2 salary, guaranteed payments show up on the partner’s Schedule K-1 (Box 4) and are always treated as ordinary income subject to self-employment tax. They don’t carry the character of the partnership’s underlying income, so a guaranteed payment is ordinary income even if the partnership’s profits come entirely from capital gains.
How Business Losses Are Treated
Loss treatment is one of the clearest practical advantages of pass-through taxation. When a partnership reports a net loss, that loss flows through to the partners’ personal returns, where it can offset wages, investment income, and other taxable income. For a business burning cash in its early years, that can produce real tax savings for the owners immediately.
There are limits. A partner can only deduct losses up to the adjusted basis of their partnership interest. If your basis is $50,000 and your share of losses is $80,000, you can only use $50,000 this year, with the remaining $30,000 carrying forward.12Internal Revenue Service. New Limits on Partners Shares of Partnership Losses Frequently Asked Questions Passive activity rules and at-risk limitations can further restrict what you deduct if you’re not actively involved in the business.
C corporation losses stay trapped inside the corporation. A loss reduces the corporation’s taxable income in the current year or carries forward to offset future corporate profits under the net operating loss rules, but it never flows to shareholders. If you invest $100,000 in a C corporation and it loses money for three years, none of those losses appear on your personal return. You only realize a loss for personal tax purposes when you sell or abandon your stock.
Health Insurance and Fringe Benefits
C corporations have a meaningful advantage on fringe benefits, particularly health insurance. A C corporation can pay health insurance premiums for owner-employees and deduct 100% of the cost as a business expense. If the corporation has a formal health plan in place, the owner-employee receives the benefit tax-free. This is one of the few areas where the C corporation structure creates savings that pass-through entities can’t easily replicate.
Partners and LLC members don’t get the same treatment. Health insurance premiums paid by the partnership on behalf of a partner are treated as guaranteed payments and included in the partner’s taxable income on their K-1. The partner can then claim an above-the-line deduction for health insurance premiums on their personal return, which offsets the income tax impact, but the premiums remain subject to self-employment tax. The net result: C corporation owner-employees save the self-employment tax on their health insurance premiums compared to partners receiving the same benefit.
Deadlines, Extensions, and Penalties
The two forms have different due dates, and the reason is practical. Partnerships file first so partners receive their K-1s in time to prepare their personal returns.
Form 1065
Form 1065 is due by the 15th day of the third month after the tax year ends. For calendar-year filers, that’s March 15.13Internal Revenue Service. Instructions for Form 1065 – U.S. Return of Partnership Income The partnership must furnish Schedule K-1s to all partners by the same date. If the deadline falls on a weekend or holiday, it shifts to the next business day.
The late filing penalty is $220 per partner for each month (or partial month) the return is late, for up to 12 months.14Internal Revenue Service. Information About Your Notice, Penalty and Interest For a five-partner LLC that files four months late, that’s $4,400. The penalty applies even though the partnership itself owes no tax. Plenty of small partnerships get hit with it simply because the owners didn’t realize the information return had an earlier deadline than their personal returns.
Form 1120
Form 1120 is due by the 15th day of the fourth month after the tax year ends. For calendar-year corporations, that’s April 15.15Internal Revenue Service. Instructions for Form 1120
The late filing penalty is 5% of the unpaid tax for each month the return is late, up to 25%. If the return is more than 60 days late, the minimum penalty is $525 or 100% of the unpaid tax, whichever is less.16Internal Revenue Service. Failure to File Penalty Unlike the flat per-partner amount on Form 1065, this penalty scales with how much tax the corporation owes.
Extensions and Estimated Payments
Both entities can request an automatic six-month extension by filing Form 7004.17Internal Revenue Service. About Form 7004, Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns For calendar-year filers, the extension pushes Form 1065 to September 15 and Form 1120 to October 15. Extensions only give you more time to file, not more time to pay. C corporations must still estimate and pay any tax owed by the original deadline to avoid interest and failure-to-pay penalties.
C corporations must also make quarterly estimated tax payments if they expect to owe $500 or more when the return is filed.18Internal Revenue Service. Estimated Taxes Partnerships don’t make estimated payments at the entity level, but individual partners must make their own quarterly estimated payments to cover the income tax and self-employment tax on their distributive shares.