Schedule K-1 Tax Form Instructions: Boxes, Deductions, and Filing

To read and file Schedule K-1, start by confirming which of the three versions you received, verify your identifying information in Part II, then move box by box through Part III, sending each amount to the specific form or schedule the IRS instruction booklet tells you to use. If any box shows a loss, run it through the basis, at-risk, and passive-activity tests in that order before claiming a deduction. You do not attach the K-1 to your personal return, but the numbers on it drive several schedules of your Form 1040.

Identify Which Schedule K-1 You Received

Three different entities issue a K-1, and the form is not identical across them:

Schedule K-1 (Form 1065) comes from a partnership. The partnership files Form 1065, and your K-1 is your slice.
Schedule K-1 (Form 1120-S) comes from an S corporation. The S corporation files Form 1120-S.
Schedule K-1 (Form 1041) comes from an estate or trust. The fiduciary files Form 1041.

The box numbering and codes differ across these three versions, so the first practical step is opening the correct instruction booklet. The partnership version is the “Partner’s Instructions for Schedule K-1 (Form 1065),” and the S corporation version is the “Shareholder’s Instructions for Schedule K-1 (Form 1120-S).”¹ Each booklet defines every code that can appear in a box and tells you which line of which form receives that amount. Keep the booklet next to the K-1 as you work.

When the K-1 Should Arrive

Calendar-year partnerships and S corporations must furnish K-1s to owners by March 15 (March 16 in 2026, because the 15th falls on a Sunday). Calendar-year estates and trusts must distribute K-1s by April 15, 2026.² If the entity extends its own return, your K-1 can come much later.

If yours has not arrived by mid-March (partnerships and S corps) or early April (trusts), contact the entity’s preparer. If it still is not in hand by April 15, file Form 4868 for an automatic six-month extension to October 15.³ The extension buys filing time only. You still have to estimate and pay by April 15 to avoid interest and late-payment penalties.

How the Form Is Laid Out

Every K-1 has three parts. Part I identifies the entity: name, address, Employer Identification Number, and the IRS service center where the main return was filed.¹ Confirm it matches the entity you expect and move on.

Part II is about you. It shows your name, taxpayer ID, and your relationship to the entity. For a partnership K-1, it also lists your profit-sharing and loss-sharing percentages and your share of partnership liabilities.⁴ Check every field. A wrong ownership percentage or a typo in your Social Security number can trigger an IRS notice, so raise it with the entity before you file.

Part III is where the numbers live. On the partnership version, the boxes run 1 through 23 and cover ordinary business income, rental income, interest, dividends, royalties, capital gains, Section 179 deductions, self-employment earnings, credits, distributions, and more.⁴ Many boxes carry an alphabetical code that further classifies the amount. Preparers frequently attach supplemental statements for items too detailed for a single box; those attachments are part of the K-1, and you need them to complete your return.

Where Each Box Goes on Your Return

Each box maps to a specific line on your Form 1040 or one of its schedules. The most common items and their destinations:

Ordinary business income or loss (Box 1) goes on Schedule E, Part II. Schedule E is the main landing zone for pass-through activity, and its totals flow to your Form 1040.
Rental real estate income or loss (Box 2) also goes on Schedule E, but the passive activity rules below apply.
Interest income (Box 5) goes on Schedule B and Form 1040, line 2b. List the entity as the payer.
Ordinary and qualified dividends (Boxes 6a and 6b) go on Schedule B. Qualified dividends in Box 6b receive the lower capital gains rate.
Short-term and long-term capital gains or losses (Boxes 8 and 9a) go on Schedule D.
Net Section 1231 gains or losses (Box 10) go on Form 4797. Net gains from Form 4797 may then flow to Schedule D as long-term capital gains.⁵
Self-employment earnings (Box 14) for general partners go on Schedule SE, where the combined Social Security and Medicare rate of 15.3% applies.⁶
Business credits (Box 15), such as the low-income housing credit or energy credits, go on Form 3800, the General Business Credit form.⁷

The instruction booklet for your specific version has a complete crosswalk covering every code. Tax software will walk you through box by box, but understanding the destination schedules helps you catch data-entry errors before the IRS does.

The Qualified Business Income Deduction

If Box 20 Code V on a partnership K-1 (or the S corporation supplemental statement) reports Section 199A qualified business income, you may deduct up to 20% of that income on your personal return.¹

Which form you use depends on your taxable income. For 2026, if your taxable income before the QBI deduction is at or below $201,750 (single) or $403,500 (married filing jointly), use Form 8995. Above those thresholds, use Form 8995-A, which applies wage and property limitations that can reduce or eliminate the deduction for certain service businesses.⁸ Picking the wrong form is a common error near the threshold. Double-check before you file.

Loss Limitations You Have to Clear

A loss on your K-1 is not automatically deductible. The IRS requires three tests in this order: basis, at-risk, passive activity. Skipping them is where most K-1 errors and penalties originate.

Basis

You can deduct losses only up to your adjusted basis in the entity. In a partnership, basis begins with your initial investment and moves with income, contributions, your share of liabilities, losses, distributions, and certain deductions. Losses in excess of basis are suspended and carry forward until you have enough basis to absorb them.⁹ The same concept applies to S corporation shareholders, though shareholders do not get basis from entity-level debt the way partners do.

S corporation shareholders must file Form 7203 to formally report stock and debt basis whenever they receive a distribution, claim a loss or deduction, dispose of stock, or receive a loan repayment from the corporation.¹⁰ Keeping a running basis worksheet each year prevents a scramble later.

At-Risk

After basis, losses are limited to the amount you are economically at risk in the activity. That generally means money you have invested and amounts you have personally borrowed and are personally liable to repay. Nonrecourse financing where you have no personal exposure does not count. Excess losses carry forward. Form 6198 handles the calculation.¹¹

Passive Activity

Passive losses generally offset only passive income, not wages, interest, or other active income. An activity is passive if you do not materially participate. The IRS defines material participation through seven tests, the most straightforward being working in the activity more than 500 hours in the tax year.¹² Meeting any one of the seven makes the income or loss nonpassive.

Rental real estate has a limited exception. If you actively participated (approving tenants, setting rents, authorizing repairs), you can deduct up to $25,000 of rental losses against nonpassive income. That allowance phases out as modified adjusted gross income rises above $100,000 and disappears at $150,000.¹² Passive losses that survive none of these exceptions are suspended until you have passive income or dispose of your entire interest. Use Form 8582 to calculate the allowable amount and track prior-year suspended losses.¹¹

Schedule K-3 for Foreign Activity

If the entity paid foreign taxes or earned foreign-source income, you may also receive Schedule K-3. It replaces the old practice of burying international items in K-1 footnotes and gives you the detail needed to claim a foreign tax credit on Form 1116.¹³ Not every partnership has to issue one. The IRS allows a domestic filing exception when all partners are U.S. persons, foreign activity is limited, and no partner requests the schedule before a specific deadline.¹⁴ If you receive a K-3, the amounts generally flow to Form 1116 or Schedule A depending on the type of foreign tax.

Health Insurance If You Own More Than 2% of an S Corporation

A shareholder owning more than 2% of an S corporation whose premiums are paid by the company will see those premiums included in W-2 wages (Box 1), though they are not subject to Social Security or Medicare tax. You then claim an above-the-line self-employed health insurance deduction on Form 1040, which reduces adjusted gross income.¹⁵ The deduction is unavailable if you or your spouse had access to a subsidized employer health plan during the same months. Owner-employees miss this benefit often.

Estimated Taxes on Pass-Through Income

K-1 income has no withholding. If yours is substantial, you owe quarterly estimated payments on Form 1040-ES, and failing to pay them can produce an underpayment penalty even when you pay the full balance at filing.

You avoid the penalty by meeting one of these safe harbors:

Current-year safe harbor: pay at least 90% of the tax shown on your 2026 return through estimated payments and withholding.
Prior-year safe harbor: pay at least 100% of the tax shown on your 2025 return. If your 2025 adjusted gross income exceeded $150,000 ($75,000 if married filing separately), the threshold rises to 110%.
Small balance exception: no penalty if the balance due after withholding and credits is under $1,000.¹⁶

The prior-year safe harbor is usually the easiest to hit because you know the target before the year starts. If your pass-through income is unpredictable, the 110% variant protects you regardless of what the current year does.

Filing and What to Keep

You do not attach the K-1 to your personal return, but you need to keep it. The IRS recommends holding tax records for at least three years from the date you filed. Underreport income by more than 25% and the retention period stretches to six years. If you are tracking basis in a partnership or S corporation, keep every K-1 and every basis worksheet until at least three years after you dispose of your entire interest, because you need them to calculate gain or loss on sale.¹⁷

The accuracy-related penalty for a substantial understatement is 20% of the underpaid tax. For most individuals, “substantial” means understating your tax by the greater of 10% of the correct tax or $5,000. If you claimed the Section 199A QBI deduction, the bar drops to 5% of the correct amount or $5,000.¹⁸ The way to stay clear is to report every K-1 item on the schedule the instruction booklet names and run through basis, at-risk, and passive-activity math before deducting any loss.

1
Internal Revenue Service. Partner’s Instructions for Schedule K-1 (Form 1065)
2
Internal Revenue Service. 2025 Instructions for Form 1041 and Schedules A, B, G, J, and K-1
3
Internal Revenue Service. Form 4868, Application for Automatic Extension of Time to File U.S. Individual Income Tax Return
4
Internal Revenue Service. Schedule K-1 (Form 1065) Partner’s Share of Income, Deductions, Credits, etc.
5
Internal Revenue Service. Instructions for Form 4797
6
Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes)
7
Internal Revenue Service. Instructions for Form 3800 and Schedule A
8
Internal Revenue Service. Instructions for Form 8995
9
Office of the Law Revision Counsel. 26 USC 704 – Partner’s Distributive Share
10
Internal Revenue Service. About Form 7203, S Corporation Shareholder Stock and Debt Basis Limitations
11
Internal Revenue Service. About Form 8582, Passive Activity Loss Limitations
12
Internal Revenue Service. Publication 925, Passive Activity and At-Risk Rules
13
Internal Revenue Service. Instructions for Form 1116
14
Internal Revenue Service. Form 1065, Schedules K-2 and K-3 Filing Requirements
15
Internal Revenue Service. S Corporation Compensation and Medical Insurance Issues
16
Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
17
Internal Revenue Service. How Long Should I Keep Records?
18
Internal Revenue Service. Accuracy-Related Penalty