Tax planning
Schedule K-1 Explained: What It Is, What the Boxes Mean, and Why It Affects Your Return
A K-1 reports your share of income, deductions, and credits from a partnership, S-corporation, trust, or estate. It doesn't go on your return by itself — the numbers flow to specific lines. Here's what each box means and what to watch for.
Written by Matt Reese, CPA · 7 min read · Published April 2026·Share on LinkedIn
Key Takeaways
- A K-1 is an informational form — it tells you your share of an entity's income, losses, deductions, and credits. It doesn't go into your return directly; each box flows to a different schedule on your personal return.
- K-1s come from partnerships (Form 1065), S-corporations (Form 1120-S), trusts and estates (Form 1041), and certain publicly traded partnerships (PTP/MLPs).
- K-1s are often the last tax documents to arrive — partnerships have until March 15 (or September 15 on extension). If you're waiting for a K-1, your return may need to be extended.
- Passive activity rules limit how partnership losses can be used. Box 1 (ordinary income/loss) from a passive activity can only offset other passive income — not wages or portfolio income.
What is a K-1 and where does it come from
Schedule K-1 is an informational tax form that reports your share of income, deductions, credits, and other tax items from a pass-through entity. Pass-through entities don’t pay income tax themselves — the income passes through to owners and is taxed on their personal returns.
You receive a K-1 if you are a:
- Partner in a partnership (Form 1065 → Schedule K-1)
- Shareholder in an S-corporation (Form 1120-S → Schedule K-1)
- Beneficiary of a trust or estate (Form 1041 → Schedule K-1)
- Unitholder in a publicly traded partnership or MLP
A K-1 doesn’t add up to one tax number. Each box flows to a different place on your personal return — and some boxes trigger complex calculations around passive activity, at-risk, and basis limits.
S-corp K-1 (Form 1120-S): key boxes
| Box | What it reports | Where it goes on your 1040 |
|---|---|---|
| Box 1 | Ordinary business income (loss) | Schedule E, Part II → then to Schedule 1 |
| Box 2 | Net rental real estate income (loss) | Schedule E, Part II |
| Box 3 | Other net rental income (loss) | Schedule E, Part II |
| Box 4 | Interest income | Schedule B |
| Box 5a | Ordinary dividends | Schedule B |
| Box 7 | Net short-term capital gain (loss) | Schedule D |
| Box 8a | Net long-term capital gain (loss) | Schedule D |
| Box 11 | Section 179 deduction | Form 4562 |
| Box 12 | Other deductions (charitable contributions, etc.) | Schedule A or other |
| Box 13 | Credits (various) | Form 3800 or specific credit form |
| Box 16 | Items affecting shareholder basis | Basis worksheet |
| Box 17 | Other information (QBI, etc.) | Schedule QBI (Form 8995 or 8995-A) |
Partnership K-1 (Form 1065): key boxes
| Box | What it reports | Notes |
|---|---|---|
| Box 1 | Ordinary business income (loss) | May be passive or non-passive depending on your role |
| Box 2 | Net rental real estate income (loss) | Almost always passive |
| Box 5 | Interest income | Taxed as ordinary income |
| Box 8 | Net short-term capital gain (loss) | Schedule D, short-term |
| Box 9a | Net long-term capital gain (loss) | Schedule D, long-term |
| Box 11 | Other income — Section 1231 gains, etc. | Form 4797 for Sec. 1231 |
| Box 13 | Other deductions | Varies — some go to Schedule A |
| Box 14 | Self-employment earnings (loss) | Schedule SE — triggers SE tax for general partners |
| Box 15 | Credits | Form 3800 |
| Box 16 | Foreign transactions | Form 1116 (foreign tax credit) |
| Box 20 | Other information (QBI, UBTI, etc.) | Multiple forms depending on item |
Box 14 — Self-employment income for general partners
The passive activity rules and K-1 losses
K-1 losses from activities in which you don’t materially participate are passive losses — they can only offset other passive income, not wages, interest, dividends, or active business income. Unused passive losses are suspended and carry forward to future years until:
- You have passive income to absorb them, or
- You dispose of the entire interest in the activity (at which point all suspended losses become deductible)
Material participationtests determine whether an activity is passive. You materially participate if you work more than 500 hours in the activity during the year, or if it’s your principal business activity, among other tests. Most S-corp owner-operators materially participate and their losses are not passive.
Passive losses from real estate partnerships pile up until you sell. The suspended losses become a significant deduction in the year you exit the investment — which is one reason real estate partnerships can be attractive for high-income investors despite years of showing no current deduction.
Basis limitations on K-1 losses
Even if a loss is active (not passive), you can only deduct a loss equal to your basis in the entity. Losses in excess of basis are suspended until basis is restored.
For S-corps: basis is stock basis plus debt basis (loans you make directly to the corporation — not bank loans the corporation takes out). For partnerships: basis includes your share of the partnership’s liabilities, which is why limited partnerships with recourse or non-recourse debt can generate losses that exceed your cash investment.
When K-1s arrive — and why they delay returns
| Entity type | Original K-1 deadline | Extended K-1 deadline |
|---|---|---|
| S-corporation (Form 1120-S) | March 15 | September 15 |
| Partnership (Form 1065) | March 15 | September 15 |
| Trust or estate (Form 1041) | April 15 | September 30 |
| Publicly traded partnership / MLP | March 15 | Varies — often arrives late |
If you receive a K-1 from a partnership or trust that extends, you typically won’t have the K-1 until September — which means your personal return must also be extended. This is normal for investors in private partnerships, real estate funds, and MLPs. File for extension by April 15 (paying estimated tax based on prior-year income) and wait for the K-1 before amending or filing the final return.
Keep your basis worksheets — forever
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ReturnsWhy Your Business and Personal Tax Returns Need to Be Coordinated
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Frequently asked
Questions owners actually ask
- Do I attach the K-1 to my personal return?
- No — K-1s are not attached to your personal return (Form 1040). The information from the K-1 is entered into your tax software or by your CPA, and the numbers flow to the appropriate schedules (Schedule E, Schedule D, etc.). If you're e-filing, nothing from the K-1 is physically attached — it's keyed in. You should keep the K-1 with your tax records for at least 7 years.
- Why does my K-1 show income even though I didn't receive any cash?
- In a pass-through entity, income is taxed when earned — not when distributed. If the partnership or S-corp made money but didn't distribute it, you still owe tax on your share of that income. This is the classic 'phantom income' issue in pass-through entities. When cash eventually comes out, it's a return of your already-taxed basis — not additional income.
- What does 'at-risk' mean on the K-1?
- The at-risk rules (Section 465) limit losses to the amount you could actually lose from the investment — your cash invested, loans you're personally responsible for, and certain other amounts. If your at-risk amount is $50,000, you can only deduct up to $50,000 in losses from that activity. Losses in excess of at-risk basis are suspended and carry forward to future years.
- I received a K-1 from a fund or limited partnership I invested in. What do I do with it?
- This is a very common situation for investors in hedge funds, private equity, or real estate partnerships. The K-1 from these investments reports your share of the fund's income, capital gains, deductions, and sometimes complex items like Section 1231 gains or unrelated business taxable income (UBTI in a retirement account). These K-1s are almost always handled by a CPA — the line items are numerous and the passive activity calculations are non-trivial.
- My K-1 arrived after I already filed my return. What do I do?
- File an amended return (Form 1040-X). Report the K-1 income as you would have originally. If the K-1 income is small and results in minimal additional tax, many people weigh whether the amendment is worth the effort — but if the IRS receives a copy of the K-1 (which they do, from the entity that filed it) and your return doesn't reflect it, you'll likely get a CP2000 notice anyway. Amending proactively is usually cleaner.
Take the next step
Turn tax questions into a plan. Talk with Matt or see how we work with operating business owners.
Educational content only.This article is for informational purposes and does not constitute tax, legal, or investment advice. Every owner’s facts are different; consult a qualified CPA and advisor before acting. Tax and accounting services are provided through Matt Reese, CPA; investment advisory services are provided through Measured Risk Portfolios, a registered investment adviser. Matt Reese, CPA and Measured Risk Portfolios are separate entities; clients are not required to engage both.