The choice between Form 1065 and Form 1120 comes down to how your business is organized. Partnerships and multi-member LLCs that haven’t elected corporate treatment file Form 1065, the U.S. Return of Partnership Income. C-corporations, and any entity that has elected to be taxed as a corporation, file Form 1120, the U.S. Corporation Income Tax Return. The difference matters beyond the paperwork: a partnership passes its income through to the owners’ personal returns, while a C-corporation pays tax itself at a flat 21% rate before anything reaches shareholders.
Who Files Form 1065
Form 1065 is required for any domestic partnership, meaning any business with two or more owners that hasn’t elected to be taxed as a corporation.1Internal Revenue Service. About Form 1065, U.S. Return of Partnership Income General partnerships, limited partnerships, and limited liability partnerships all fall into this category.
Multi-member LLCs file Form 1065 by default. Unless the LLC affirmatively files Form 8832 to elect corporate treatment, the IRS classifies any LLC with more than one member as a partnership.2Internal Revenue Service. Limited Liability Company – Possible Repercussions Single-member LLCs are a different story: they’re disregarded entities that report on the owner’s individual return and don’t file Form 1065 at all.
Form 1065 is an informational return. The partnership itself owes no federal income tax. It reports total income, deductions, gains, and losses, and those amounts flow through to each partner’s personal return through a Schedule K-1.3Internal Revenue Service. Partnerships The return is due March 15 for calendar-year partnerships.
Who Files Form 1120
Form 1120 is for domestic corporations that haven’t elected S-corporation status. Any entity incorporated under state law that doesn’t file an S election is treated as a C-corporation by default.4Internal Revenue Service. Instructions for Form 1120 Entities that affirmatively elect corporate classification through Form 8832 file here too.5Internal Revenue Service. About Form 8832, Entity Classification Election
Unlike Form 1065, Form 1120 is not just informational. The corporation calculates its own taxable income and pays federal income tax directly to the IRS at a flat 21% rate on all taxable income, regardless of amount.6Internal Revenue Service. About Form 1120, U.S. Corporation Income Tax Return Calendar-year corporations file by April 15.
Where the S-Corporation Fits
Neither form applies to an S-corporation, which files its own return on Form 1120-S. An S-corporation is legally a corporation, but for tax purposes it acts like a partnership, passing income through to shareholders rather than paying corporate tax.7Internal Revenue Service. About Form 1120-S, U.S. Income Tax Return for an S Corporation
Not every corporation qualifies. The entity must be domestic, have 100 or fewer shareholders (all individuals, certain trusts, or estates), have no nonresident alien shareholders, issue only one class of stock, and not be an ineligible entity such as certain banks, insurance companies, or international sales corporations.8Internal Revenue Service. S Corporations The election is made on Form 2553, filed no later than two months and 15 days after the start of the tax year the election is to take effect. If a corporation doesn’t qualify or misses the deadline, it files Form 1120 as a C-corporation until a valid election is in place.
Pass-Through vs. Entity-Level Tax
The core difference between the two forms is who writes the check to the IRS.
Partnerships use pass-through taxation. The entity reports its income but doesn’t pay tax on it. Each owner’s allocated share of profit or loss flows to their personal Form 1040 on a Schedule K-1, and they pay tax at their individual rate.3Internal Revenue Service. Partnerships That income is taxable to the partner whether or not they actually received a distribution, a detail that catches many newer partners off guard. For 2026, individual rates run from 10% to a top rate of 37%, which applies to taxable income above $640,600 for single filers and $768,700 for married couples filing jointly.9Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 Pass-through owners with qualifying income may also claim the Section 199A qualified business income deduction, which reduces taxable income by up to 20% of qualified business income and was extended by the One Big Beautiful Bill Act.10Office of the Law Revision Counsel. 26 U.S. Code 199A – Qualified Business Income The deduction phases out for higher earners in certain service-based industries and is subject to wage and property limitations above specified income thresholds.
C-corporations take the opposite approach. The corporation pays tax on its profits at the flat 21% rate. When it distributes the remaining after-tax profits as dividends, those dividends are taxed again at the shareholder’s individual level. Qualified dividends are taxed at the preferential long-term capital gains rates of 0%, 15%, or 20%, depending on the shareholder’s income.11Internal Revenue Service. Topic No. 404, Dividends and Other Corporate Distributions High-income shareholders also owe the 3.8% net investment income tax on top of the dividend rate.12Internal Revenue Service. Net Investment Income Tax
Run the math on a dollar of corporate profit going to a top-bracket shareholder. The corporation pays 21 cents in tax, leaving 79 cents. The shareholder then pays 23.8% on that 79 cents (20% plus the 3.8% NIIT), or about 18.8 cents. Total federal tax: nearly 40 cents on the dollar. That double taxation is the defining tradeoff of the C-corporation structure.
Owner Pay and Employment Taxes
How you pay yourself, and what employment taxes you owe on that pay, also depends on which form your business files.
In a partnership, partners who work in the business are typically compensated through guaranteed payments, which function like a salary but are a partnership-level deduction. The partnership deducts them on Form 1065, and they show up on the partner’s K-1 as taxable income subject to self-employment tax.13Internal Revenue Service. Partners Instructions for Schedule K-1 (Form 1065) Partners may also take draws, but a draw isn’t a separate income event: the partner is already taxed on their full distributive share whether the cash stays in the business or comes out.
General partners and members of multi-member LLCs taxed as partnerships owe self-employment tax of 15.3% on their share of ordinary business income.14Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes) That’s 12.4% for Social Security on earnings up to $184,500 in 2026 and 2.9% for Medicare on all earnings.15Social Security Administration. Contribution and Benefit Base Earnings above $200,000 for single filers ($250,000 for joint filers) also face an additional 0.9% Medicare surtax. Limited partners get an important exception: under IRC 1402(a)(13), a limited partner’s distributive share is excluded from self-employment tax, and only guaranteed payments for services the limited partner actually performed are subject to SE tax.16Internal Revenue Service. Self-Employment Tax and Partners
In a C-corporation, a shareholder who works in the business must receive a W-2 salary, and the IRS requires that salary to be reasonable for the services actually performed. The corporation can’t disguise profit distributions as salary to inflate its deduction, and it can’t set salary artificially low to dodge payroll taxes. The W-2 salary is a deductible expense that reduces the corporation’s taxable income on Form 1120.17Internal Revenue Service. About Form W-2, Wage and Tax Statement After-tax profits distributed to shareholders come out as dividends, reported on Form 1099-DIV, and are not deductible by the corporation.18Internal Revenue Service. About Form 1099-DIV, Dividends and Distributions Shareholders don’t pay self-employment tax on dividends, but they do pay the employee’s share of FICA on any salary.
What Happens When the Business Loses Money
Where losses land can be the deciding factor between the two forms, especially for early-stage businesses.
In a partnership, losses pass through to each partner’s K-1 just like income. Claiming them isn’t automatic. A partner can only deduct losses up to their outside basis in the partnership, which is essentially their invested capital plus allocated income minus distributions and previously claimed losses. At-risk rules and passive activity loss rules may further restrict how much of a loss a partner can actually use in a given year. Losses that can’t be used carry forward until the partner has enough basis, at-risk amount, or active participation to absorb them. For 2026, individual taxpayers also face the excess business loss limitation: combined business losses can’t exceed $256,000 for single filers or $512,000 for joint filers. Any amount beyond those thresholds is treated as a net operating loss carried forward.
C-corporations handle losses at the entity level. The corporation can carry forward net operating losses indefinitely, but the deduction in any year is limited to 80% of taxable income, leaving the remaining 20% exposed to tax.19Office of the Law Revision Counsel. 26 USC 172 – Net Operating Loss Deduction Corporate losses do not pass through to shareholders. If your business expects to lose money for several years, that’s a real disadvantage of C-corporation status, because pass-through treatment lets owners use those losses on their personal returns.
Filing Deadlines and Penalties
Form 1065 is due March 15 for calendar-year partnerships. Form 1120 is due April 15 for calendar-year corporations. Both deadlines shift to the next business day when they fall on a weekend or holiday. Either entity can request an automatic six-month extension by filing Form 7004 before the original due date.20Internal Revenue Service. Instructions for Form 7004 An extension gives extra time to file, not extra time to pay; estimated payments must still be made by the original deadline.
Late-filing penalties work very differently between the two forms. Partnership penalties are calculated per partner. For returns due after December 31, 2025, a late Form 1065 incurs a penalty of $255 per partner for each month or partial month the return is late, up to 12 months.21Internal Revenue Service. Failure to File Penalty A five-partner partnership that files six months late would owe $7,650, and the penalty applies even though the partnership itself owes no income tax.
Corporation penalties are based on unpaid tax. A late Form 1120 triggers a penalty of 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 the lesser of the tax due or $525 for returns required to be filed in 2026. A separate failure-to-pay penalty of 0.5% per month runs alongside.
Partners receiving K-1 income typically need to make quarterly estimated tax payments, because no employer is withholding on their behalf.22Internal Revenue Service. Estimated Tax for Individuals (Form 1040-ES) C-corporations have their own quarterly estimated tax obligations and generally must make deposits if the corporation expects to owe $500 or more for the year.