Both returns report a business's income without the business itself paying federal income tax. The income passes through to the owners on Schedule K-1 and lands on their personal returns. The similarity ends there. Which form you file follows from how the business is classified, and that classification shapes self-employment tax, how you pay yourself, how profits can be split, and how much loss you can deduct.
Who files which
- Form 1065 is the partnership return. It is filed by general and limited partnerships and by multi-member LLCs that have not elected otherwise, because the IRS treats a multi-member LLC as a partnership by default.
- Form 1120-S is the S corporation return. It is filed by corporations that elected S status and by LLCs that elected to be taxed as S corporations on Form 2553.
- A single-member LLC with no election files neither. Its activity goes on the owner's Form 1040, usually on Schedule C.
Both returns are due on the 15th day of the third month after the year ends, which is March 15 for calendar-year businesses, and both can be extended six months to September 15 with Form 7004. Filing late is expensive: the penalty is charged per owner for each month the return is late, for up to twelve months, even when the business owes no tax.
The differences that matter
| Form 1065 (partnership) | Form 1120-S (S corporation) | |
|---|---|---|
| Self-employment tax | Active owners generally owe it on their share of business income and on guaranteed payments | Owners owe payroll tax only on W-2 wages; distributions are not subject to it |
| How owners are paid | Guaranteed payments and draws, no W-2 | A reasonable W-2 salary first, then distributions |
| Splitting profit | Can differ from ownership if the agreement gives the split real economic effect | Strictly in proportion to shares, always |
| Who can own it | Anyone, including companies, trusts and non-U.S. persons | Up to 100 owners who are individuals, certain trusts or estates; no entities or nonresident aliens |
| Basis for deducting losses | Includes the owner's share of business debt | Includes only what the owner invested, plus loans the owner made directly |
| Moving property in or out | Usually tax-free | Distributing appreciated property triggers gain |
| Audits | Partnership-level audit rules with a partnership representative | Adjustments flow to the shareholders |
A few of these deserve a closer look.
Self-employment tax
This is the reason most owner-operated businesses consider the S corporation. A partner who works in the business generally pays self-employment tax on the whole distributive share. An S corporation owner pays payroll tax on a reasonable salary and nothing on the rest. The IRS has been challenging LLC members who claim the limited-partner exception to self-employment tax, so do not count on that route for an active owner.
Allocations
Partnerships are flexible. Two owners can split profits 70/30 while owning 50/50, as long as the agreement is written to give those allocations real economic effect. An S corporation cannot. Every dollar of income, loss and distribution follows share ownership, and an agreement that says otherwise can be treated as a second class of stock, which ends the election.
Basis and losses
Owners can deduct losses only up to their basis. A partner's basis includes a share of the partnership's debt, which is why real estate partnerships can pass through losses created by mortgage-financed depreciation. An S corporation shareholder gets basis only for what they personally invested or lent. For a leveraged business, that difference decides whether losses are usable now or suspended.
Property
Moving property into or out of a partnership is usually tax-free. Taking appreciated property out of an S corporation is treated as a sale at fair market value, with the gain passed to the owners. Businesses that expect to hold real estate or other appreciating assets inside the entity should weigh this before electing.
Which tends to fit
- An operating business where the owners do the work, with steady profit, usually benefits from the S corporation once the reasonable-salary math works. Our guide to the S-Corp election covers that decision.
- Real estate holdings, investment partnerships, businesses with entity or foreign owners, and any business that needs to allocate profits differently from ownership usually belong on Form 1065.
- Some owners run both: an S corporation for the operating company and a partnership that owns the building. The right structure is often more than one entity.
Switching from one to the other
A multi-member LLC taxed as a partnership can elect S status by filing Form 2553; the IRS treats the LLC as having converted. The election itself is usually clean, but the operating agreement, any debt that currently supports owner basis, and built-in gains on appreciated property all need review first. Going the other direction, from S corporation back to partnership, is harder and can trigger tax on the way out.
What goes on your personal return
Whichever form the business files, each owner receives a Schedule K-1 reporting their share of income, deductions and credits, and reports it on Form 1040. The K-1 arrives after the business return is done, which is why business returns are due a month before personal returns. If your business extends, plan on extending your personal return too.
Book a Discovery Call to review which return fits the way your business actually operates.
This guide is general information for small business owners, not advice for your specific situation. Tax law changes and the details matter, so talk with a professional before acting.
Sources: IRS, About Form 1065 · IRS, About Form 1120-S · IRS, About Form 2553