Schedule K-1 Explained: How K-1 Income Is Taxed for High-Income W-2 Families

By Kevin Luu, Co-Founder and Chief Learning Officer. Reviewed on 2026-09-30.

A Schedule K-1 is the statement a partnership, S corporation, estate or trust sends each owner (or, for an estate or trust, each beneficiary) to report that person’s share of its income, losses, deductions and credits. You pay tax on your share whether or not the partnership sent you any cash, and you report each box on your own Form 1040 (ordinary income on Schedule E, interest on Schedule B, capital gains on Schedule D). The K-1 itself stays in your files; the IRS instructions say not to attach it unless you are specifically required to.

For a two-earner household in California or Washington, K-1s usually arrive after the RSU proceeds get invested: a venture or private equity fund, a real estate syndication, a family LLC, or a medical group partnership. This guide explains how that income is taxed at your bracket, with a worked example.

Where K-1s come from in a high-income W-2 household

There are three versions of the form, and you may get all three in one year:

• Schedule K-1 (Form 1065) from a partnership or multi-member LLC. This is the common one: private equity, venture, hedge and real estate funds, and physician or dental group partnerships.
• Schedule K-1 (Form 1120-S) from an S corporation, for example a consulting company one spouse owns.
• Schedule K-1 (Form 1041) from an estate or a trust that distributed income to a beneficiary. If you fund a trust for your children, they may be the ones receiving this form.

The partnership itself generally pays no federal income tax. The IRS partner instructions put it plainly: “you may be liable for tax on your share of the partnership income, whether or not distributed” (Partner’s Instructions for Schedule K-1 (Form 1065)). That single rule explains most K-1 surprises.

How each K-1 box lands on your Form 1040

A K-1 is not taxed at one rate. Each box keeps its character, so the same form can hold wage-like income, investment income and losses you cannot use yet.

Box-by-box line numbers are covered in our guide to where K-1 income goes on the 1040 and in how to read a Schedule K-1.

Is K-1 income self-employment income?

Sometimes. It depends on your role, not the form. A general partner, or an LLC member who works in the business, usually has self-employment earnings in box 14. A limited partner in an investment fund generally does not, except for fixed payments it receives for services (reported in box 4). Most LP interests held by W-2 families produce no self-employment tax at all.

When it does apply, self-employment tax is 15.3%: 12.4% for Social Security and 2.9% for Medicare (IRS, Self-Employment Tax). The Social Security part stops at the wage base, which is $184,500 for 2026 (IRS Pub 15), and your W-2 wages count first. So an Apple engineer earning $450,000 in salary and RSUs who also has box 14 earnings from a side consulting LLC owes no 12.4% on those earnings, only the 2.9% Medicare part, plus the 0.9% Additional Medicare Tax once combined wages and self-employment income pass $250,000 on a joint return for 2026.

The picture changes for a physician who moves from a W-2 at a hospital to partnership in a medical group. There is no W-2 wage base to use up, so the full 12.4% applies to the first $184,500 of net earnings for 2026. Whether K-1 income counts as earned income for IRA and other purposes is covered in does K-1 income count as earned income.

Worked example: a $900,000 California household with two fund K-1s

Assumptions, for illustration only: married filing jointly in San Mateo, $900,000 of combined W-2 wages including RSU vests, $24,500 each into their 401(k)s for 2026, standard deduction of $32,200. Federal taxable income before any K-1 is $818,800, already in the 37% bracket (over $768,700 for 2026). Using RSU sale proceeds, they invested in two limited partnerships. Their 2026 K-1s show:

• Growth equity fund: $12,000 interest (box 5), $40,000 long-term capital gain (box 9a), $10,000 cash distributed.
• Real estate syndication: $22,000 rental loss from depreciation (box 2), $15,000 cash distributed.

Three things stand out. First, the family owes $19,877 on $52,000 of K-1 income, about 38%. California has no lower rate for capital gains, so the $40,000 gain is taxed like salary at the state level. (The California figure assumes $850,000 of state taxable income before the K-1s; 2026 California brackets were not yet published, so 2025 rates are used.)

Second, the $22,000 real estate loss does nothing this year. Passive losses can offset only passive income, and interest and capital gains from the fund are portfolio income, which does not count (IRS Pub 925). The $25,000 rental loss allowance phases out completely once modified AGI reaches $150,000, and limited partners generally cannot use it at all, so it is gone for this household. The loss carries forward and is typically released when there is passive income or when the family disposes of its entire interest in the activity (for example, when the syndication sells the property).

Third, the $25,000 of cash they received is not what they are taxed on. Distributions are generally tax-free until they exceed your basis. Tax follows the K-1 income, and cash follows the fund’s decisions. In some years you will owe tax with little or no cash to pay it.

The same K-1s for a Washington household

An Amazon family in Bellevue with the same wages and K-1s owes the same $14,416 federal. Washington has no individual income tax for 2026, so the interest is not taxed by the state (WA DOR). The $40,000 gain can be subject to Washington’s 7% capital gains tax: the tax applies to individuals, including through “their ownership interest in a pass-through or disregarded entity” (WA DOR, capital gains tax). It only bites once the household’s total Washington long-term gains for the year pass the standard deduction ($278,000 for 2025, the latest published). A year in which they also sell a large block of long-held company stock can push them over.

Two Washington caveats for this reader. Gains above $1,000,000 are taxed at 9.9%. And a 9.9% income tax on AGI over $1,000,000 takes effect January 1, 2028. K-1 income that lands in AGI would likely count toward it, but the Department of Revenue has not yet issued detailed guidance on how income is defined.

Timing: why K-1 families often extend

A partnership must give you your K-1 by its own return due date, March 15 for a calendar-year partnership, and later if it extends (Form 1065 instructions). Private funds extend often. That is why many families with K-1s file Form 4868 for an automatic six-month extension (to October 15 for most calendar-year filers). The extension covers filing, not paying: tax not paid by the April due date accrues interest (Form 4868 instructions), so you still estimate and pay by April.

K-1 income has no withholding. For households with AGI over $150,000, the underpayment penalty is generally avoided if payments reach at least 110% of last year’s tax or 90% of this year’s (IRS Pub 505). W-2 earners have an easier option than quarterly checks: raise withholding on salary or RSU vests. Withholding is treated as paid evenly through the year, even if it happens in December. Many companies withhold on RSUs at the 22% optional flat rate, which already falls well short of a 37% bracket, so K-1 income widens a gap that often exists anyway. Our K-1 tax rate guide goes deeper on rates by box.

Common mistakes we see with K-1s

• Filing before the K-1 arrives. Estimating the numbers and amending later often costs more than extending.
• Treating distributions as income, or ignoring basis. Keep a running basis record per partnership. Your preparer needs it when you sell or when losses exceed basis.
• Expecting real estate losses to offset RSU income. At this income, they generally do not.
• Missing state filings. A fund that operates in other states can create a filing requirement there, and entities filing in California issue a separate California K-1 (Schedule K-1 (565) from a partnership, Schedule K-1 (568) from an LLC) whose amounts can differ from federal because California does not follow many recent federal changes.
• Forgetting capital calls. A committed fund can call cash for years. It belongs in the cash plan next to tax payments.

What to document for your children

LP interests outlive the people who bought them. If something happens to you, your children (or their guardian and trustee) inherit commitments, capital calls, K-1s arriving in September and a basis history nobody else knows. Write down each partnership, why you invested, what is still committed, who the contact is, and where the basis records live. If you give LP units to a child’s custodial account, note that for a child under 18 the child’s unearned income over $2,700 for 2026 is generally taxed at your rate under the kiddie tax (Rev. Proc. 2025-32). A trust that keeps the income instead pays tax at trust rates, and income it distributes to the child is taxed to the child. Conversations fade. Documentation compounds.

Frequently asked questions

Do I attach my K-1 to my tax return?

Generally no. The IRS partner instructions say to keep the K-1 for your records and not file it with your return unless you are specifically required to. You report its numbers on the right schedules of your Form 1040, and the partnership files its own copy with the IRS, which is how the IRS matches the two.

Can I file my return before my K-1 arrives?

You can, but you would be estimating and may need to amend. For funds that routinely extend, filing Form 4868 for an automatic extension is the usual path. The extension does not delay payment, so make an estimated payment by the April deadline based on last year’s K-1s and what the fund has told you.

Is a K-1 from an S corporation taxed the same way?

The pass-through idea is the same: you pay tax on your share whether or not it is distributed. The main difference is self-employment tax. S corporation income on the K-1 is not subject to self-employment tax, but an owner who works in the business is expected to take reasonable W-2 salary, which carries payroll tax.

Your next step

List every entity that sends you a K-1, the date each one arrived last year, and whether it included cash. That list tells you whether to extend, how much to add to withholding, and what to write down for your family. If you want a second set of eyes on how K-1s fit with your RSUs and withholding, see our tax management and investment and risk management services, or book a Tax & Wealth Assessment.

This is general education, and the right move depends on your family’s full picture.

Written by

Kevin Luu

Co-Founder and Chief Learning Officer, Bright Advisers

Kevin has advised high-income W-2 tech and biotech families since 2015, and leads the education-first Age Five Family Office from Brea, California.

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