K-1: 1120-S vs 1065
Two forms with the same name and materially different consequences. Self-employment tax, basis, and debt all behave differently depending on which one arrives.
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Quick answer
A 1120-S K-1 reports an S corporation shareholder's share; a 1065 K-1 reports a partner's share. The partnership version adds guaranteed payments and a share of entity liabilities. Partnership trade or business income is generally subject to self-employment tax; S corporation K-1 income generally is not.
Both forms are called Schedule K-1 and both report a pass-through owner's share of entity activity. That is where the similarity ends. The box numbering differs, the partnership version reports items the S corporation version has no concept of, and the tax consequences diverge in ways that routinely surprise owners who have held both.
The two differences that matter most are self-employment tax and basis. Everything else is detail.
The Structural Differences
Four divergences that drive real dollars.
| 1065 K-1, partnership | 1120-S K-1, S corporation | |
|---|---|---|
| Self-employment tax | Generally applies to a general partner's trade or business share | Generally does not apply; payroll tax runs through W-2 salary instead |
| Owner compensation | Guaranteed payments, reported on the K-1 | W-2 wages, reported separately from the K-1 |
| Share of entity debt | Reported and included in basis | Not reported and not included in stock basis |
| Allocation flexibility | Special allocations permitted with substantial economic effect | Strictly pro rata by share ownership |
| Ownership restrictions | Few; entities and foreign partners permitted | Limited shareholder count, one class of stock, eligibility rules |
Box by Box Comparison
Where the same information lives on each form.
| Item | 1065 K-1 | 1120-S K-1 |
|---|---|---|
| Ordinary business income | Box 1 | Box 1 |
| Net rental real estate income | Box 2 | Box 2 |
| Guaranteed payments | Box 4 | No equivalent |
| Interest income | Box 5 | Box 4 |
| Section 179 deduction | Box 12 | Box 11 |
| Self-employment earnings | Box 14 | No equivalent |
| Qualified business income data | Box 20, code Z | Box 17, code V |
| Share of liabilities | Part II, item K | Not reported |
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Basis, Debt, and Deductible Losses
The technical difference with the largest dollar consequence.
You can only deduct losses up to your basis. Partnerships and S corporations calculate that limit very differently, and the difference determines whether a leveraged business generates usable deductions.
Worked example
You contribute $50,000 to a business that borrows $400,000 and generates a $150,000 loss allocated to you in year one.
As a partnership
As an S corporation
Illustrative only, ignoring at-risk and passive activity limits which apply on top. The suspended loss is not lost, but it does not reduce this year's tax.
Loans to the corporation are not the same as guarantees
An S corporation shareholder creates debt basis only by lending money directly to the corporation. Personally guaranteeing a bank loan to the corporation does not create basis, despite putting the shareholder on the hook economically. This distinction has been litigated repeatedly and consistently resolved against taxpayers.Because basis is calculated by the owner rather than the entity, and because entities do not always track it, reconstructing basis years later during a sale is a common and expensive exercise. The practice of tracking it annually is covered in the owner basis guide.
What to Do When Your K-1 Arrives
Four checks before it goes into your return.
Check the ownership percentages in Part II
Confirm they match your understanding of the deal. Errors here propagate through every allocated number on the form.
Read every attached statement
Coded boxes reference supplemental schedules that carry the detail. A K-1 without its attachments is incomplete and cannot be entered correctly.
Reconcile the capital account rollforward
Beginning balance, contributions, income, distributions, and ending balance should tie. A break usually indicates an entity-level error worth resolving before filing.
Expect to extend your own return
Entities that extend to September deliver K-1s after the individual April deadline. Extending is routine for K-1 recipients, not a sign that anything is wrong.
The entity side of the partnership version is covered in the Form 1065 guide, and the general anatomy of a K-1 is in the Schedule K-1 overview. Professional service partners should read the partner tax guide, real estate investors should start with entity selection, and anyone considering restructuring should look at the buy-in and buy-out guide alongside the LLC filing overview. For owners eventually selling the business, the business sale guide explains why basis tracking matters long before the exit.
Receiving a K-1 You Do Not Fully Understand?
Box 17 and box 20 codes carry basis limits, at-risk limits, and passive activity consequences that most software handles poorly. A Taxstra CPA will read it properly. The initial consultation is free.
Tax planning slots are limited before year-end.
Frequently Asked Questions
What is the difference between a K-1 from Form 1120-S and Form 1065?
A 1120-S K-1 comes from an S corporation and a 1065 K-1 comes from a partnership. The box numbering differs, partnership K-1s report guaranteed payments and a share of liabilities that S corporation K-1s do not, and the basis and self-employment tax consequences are substantially different.
Is K-1 income subject to self-employment tax?
Generally yes on a partnership K-1 for a general partner, where the distributive share of trade or business income flows to Schedule SE. Generally no on an S corporation K-1, where the shareholder pays payroll tax on their reasonable salary instead. That difference is the core of the S corporation planning case.
What is a guaranteed payment on a partnership K-1?
A guaranteed payment is compensation to a partner determined without regard to partnership income, reported in box 4 of a 1065 K-1. It is deductible to the partnership and ordinary income to the partner, and it is generally subject to self-employment tax. S corporation K-1s have no equivalent because owners take a W-2 salary instead.
Why does my K-1 show income I never received?
Pass-through entities allocate income to owners whether or not cash was distributed. You are taxed on your allocated share, not on what hit your bank account. A profitable business that reinvests everything still produces taxable K-1 income for its owners, which is why distributions for taxes are negotiated in advance.
How does basis differ between an S corporation and a partnership?
Partnership basis includes a share of entity liabilities, so debt increases the amount of loss a partner can deduct. S corporation stock basis does not include entity-level debt; only direct shareholder loans to the corporation create debt basis. This is the single most consequential technical difference between the two forms.
When do I receive my K-1?
Both partnership and S corporation returns are due March 15 for calendar-year entities, with a six month extension available to September 15. Because many entities extend, K-1s frequently arrive after the individual April deadline, which is why K-1 recipients often extend their own returns as a matter of routine.
The Entity Choice Matters More Than the Form
Partnership versus S corporation drives self-employment tax, basis, and how much you can actually deduct. That decision is worth far more than reading the K-1 correctly. Book a free initial consultation.
Tax planning slots are limited before year-end.
Next Steps
Filing it yourself is fine. Optimizing it is where the money is.
Getting the form right keeps you out of trouble. The strategies below are what actually lower the bill.
Owner basis management
The limit that decides whether a loss is deductible now or suspended for years.
Form 1065 explained
The partnership return that produces the K-1, and the per-partner penalty behind it.
Entity selection for investors
The choice that determines which of these K-1s you receive in the first place.
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Tax planning slots are limited before year-end.
Authoritative Sources
- IRS Schedule K-1 (Form 1065) Partner Instructions
- IRS Schedule K-1 (Form 1120-S) Shareholder Instructions
- IRS Publication 541, Partnerships
- IRS S Corporation Compensation and Medical Insurance Issues
- IRC Section 704(d), Limitation on Allowance of Losses
Citations reflect U.S. federal tax law as of the article's last reviewed date.
Related Pass-Through Entity Guides
Form 1065 Explained
The partnership return, its deadline, and the per-partner late penalty.
Owner Basis Management
Tracking basis before you need it, rather than reconstructing it at exit.
Law Firm Partner Taxes
Guaranteed payments, quarterly estimates, and equity partner mechanics.
LLC Tax Filing
How an LLC is actually taxed, and which return it owes.