Big Law Equity Partner Tax Planning: K-1, SE Tax, AMT, and Quarterly Estimates

Making equity partner is a financial milestone — and a tax shock. You've crossed from W-2 employee to self-employed partner in a pass-through entity, and the IRS treats you very differently. Here's what changes, what it costs, and how equity partners at AmLaw firms plan around it.

The K-1 transition: how partnership income is taxed

As an equity partner in a law firm partnership (or LLP), you're no longer receiving a salary subject to withholding. Instead, you receive a Schedule K-1 each year — sometimes as late as March — reporting your distributive share of firm income, deductions, and credits. That income is taxable whether or not the firm actually distributed cash to you. If the firm retained earnings or allocated income to your capital account on paper, you still owe tax on it.

The practical consequence: partners often owe far more in taxes than they expect the first year, because nothing was withheld. First-year partners at AmLaw 100 firms routinely face a combined federal + state tax bill of $300K-$600K with no paycheck withholding to offset it.

Self-employment (SE) tax on K-1 income

The most surprising tax for new partners: self-employment tax. As a W-2 associate, you paid 7.65% FICA (split with the firm). As an equity partner, you pay both halves — the full 15.3% on the first tranche of SE income, plus 2.9% Medicare above the Social Security wage base, plus 0.9% Additional Medicare Tax above high-income thresholds.

2026 SE tax structure:

• 12.4% Social Security tax on the first $184,500 of net self-employment income — maximum $22,878.¹
• 2.9% Medicare tax on all net self-employment income above the SS wage base — uncapped.
• 0.9% Additional Medicare Tax on SE income above $200,000 (single) / $250,000 (married filing jointly) — not matched by any employer deduction.²
• Half of SE tax is deductible from gross income (but not self-employment income). On $500K of SE income, the above-the-line deduction is roughly $26,700 — meaningful but not nearly enough to offset the tax itself.

§199A QBI deduction: why law firm partners mostly don't qualify

The §199A Qualified Business Income (QBI) deduction — made permanent by the One Big Beautiful Bill Act (OBBBA, July 2025) — lets pass-through business owners deduct up to 20% of qualified business income. It's a significant break for many self-employed professionals. Law firm partners largely miss it, for a specific reason: law firms are Specified Service Trades or Businesses (SSTBs).

The IRS defines SSTBs to include legal services — businesses where the "principal asset is the reputation or skill of its employees or owners." That's a law firm. As an SSTB, the §199A deduction phases out as taxable income rises above the threshold, and vanishes completely before most Big Law partners are even a factor.

2026 §199A SSTB phase-out thresholds (post-OBBBA, inflation-adjusted):

• Phase-out begins: $201,775 (single) / $403,500 (MFJ)³
• Phase-out range expanded by OBBBA: $75,000 (single) / $150,000 (MFJ)
• Full phase-out (no QBI deduction): $276,775 (single) / $553,500 (MFJ)

A Big Law equity partner earning $700K as a single filer is approximately $424K above the complete phase-out. The QBI deduction is zero. This applies regardless of the number of years in partnership or how the firm structures the payments.

The one exception worth knowing: if you operate an investment activity through the firm — limited partnership income, certain passive investment flows — that portion may qualify as non-SSTB income and retain §199A eligibility. This is rare in pure law firm structures and requires careful analysis of the K-1 line items.

Quarterly estimated tax payments on volatile distribution income

Partnership distributions aren't paid monthly or bi-weekly like a salary. Big Law firms typically distribute earnings quarterly — often with an annual true-up in Q4 based on final year performance. This creates a dangerous trap: you may receive $300K in Q4, owe substantial estimated tax by January 15, and have no withholding buffer.

The safe harbor rules: The IRS will waive underpayment penalties if you pay either (a) 90% of the current year's tax liability, or (b) 100% of the prior year's tax (110% if prior-year AGI exceeded $150,000). For Big Law partners, the prior-year 110% safe harbor is usually the more practical target — it creates a fixed, knowable number based on last year's return regardless of how much this year's income swings.

Practical strategy for volatile distribution income: Partners receiving large performance-based distributions should set aside 45-50% of each distribution into a dedicated tax account as it arrives, then make estimated payments using that reserve. A specialist advisor builds a cash-flow model that accounts for guaranteed payments (which arrive on schedule) separately from performance distributions (which are unpredictable). The goal is to be at 110% of prior-year liability by January 15 while avoiding over-paying throughout the year.

Alternative Minimum Tax (AMT) exposure

The OBBBA (July 2025) changed the AMT structure significantly for high-income taxpayers, restoring the pre-TCJA phaseout thresholds and increasing the phaseout rate. Big Law partners earning above $500K as single filers or $1M as married filers now face meaningful AMT recalculation risk.

2026 AMT parameters (post-OBBBA):

• AMT exemption: $90,100 (single) / $140,200 (MFJ)⁴
• Exemption phaseout begins: $500,000 (single) / $1,000,000 (MFJ)
• Phaseout rate: 50 cents per dollar (increased from 25% under TCJA)
• AMT rate: 26% on first $232,600 of AMTI, 28% above that

For a single partner with $800K in ordinary income: the AMT exemption phases out at 50% of ($800K − $500K) = $150,000 reduction, leaving an exemption of only $90,100 − $150,000 = $0 (fully phased out). Their alternative minimum taxable income is calculated without the standard deduction, without the §199A deduction (if any), and without state income tax deductions — and then compared against regular tax. If AMT exceeds regular tax, they pay the difference.

High-risk AMT triggers for law firm partners include: large ISO (incentive stock option) exercises from prior employer equity, accelerated depreciation on any rental or business property, and certain tax preference items from K-1s. Partners pursuing tax shelter strategies should run an AMT calculation before executing.

Net Investment Income Tax (NIIT) on top of everything

The 3.8% NIIT applies to the lesser of (a) your net investment income or (b) the amount by which your MAGI exceeds $200,000 (single) / $250,000 (MFJ).⁵ These thresholds are NOT inflation-adjusted — the same dollar amounts since 2013.

For Big Law equity partners, net investment income typically includes:

• Taxable brokerage account dividends and interest
• Capital gains from securities sales
• Passive rental income (if you own investment real estate)
• Passive K-1 income from limited partnership investments

Active K-1 income from your law firm is NOT subject to NIIT — it's subject to SE tax instead. But the ordinary income from the firm raises your MAGI well above the NIIT threshold, meaning all of your investment income is caught. A partner with $400K in K-1 income and $80K in dividend/interest income pays 3.8% on the full $80K — an extra $3,040 that no withholding captured.

State income tax: the multi-state nexus problem

Large law firms often have offices in multiple states, and partners who travel to client sites, attend depositions, or work in multiple offices may face income tax obligations in states where they spend significant time working. This is different from being a resident of a high-tax state — it's a "source state" obligation.

The key rules by state:

• New York: Taxes nonresidents on NY-source income. Partners at firms with significant NY operations who work in NY offices even occasionally may owe NY personal income tax (top rate 10.9% in NYC, 6.85% elsewhere in NY state).
• California: Taxes all income from CA-source services regardless of where the partner is domiciled. A CA-based client with significant California work creates CA nexus.
• Connecticut: Applies nexus for days worked in CT, with a factor-presence standard for partnerships.
• Illinois, New Jersey, Massachusetts: All have their own partnership income sourcing rules. The combined multi-state tax burden for a traveling partner can easily add 3-7% to effective tax rate on applicable income.

Most state law firms allocate income via partnership agreement based on where work is billed or performed. Your K-1 should include state-specific income allocations — read the state supplemental schedules carefully before assuming your home-state return captures everything.

Year-end tax planning checklist for equity partners

The following planning moves apply specifically to law firm equity partners and must be evaluated before December 31:

• Maximize retirement plan contributions. Equity partners can contribute to a solo 401(k) (up to $24,500 in 2026 employee deferrals, plus 20% of net SE income as employer contribution) or SEP-IRA (25% of net SE income, max $70,000 in 2026). If your firm has a qualified plan, contribute the maximum and model whether a personal plan layered on top makes sense.
• NQDC election deadline. December 15 is the typical deadline for electing next year's NQDC deferrals. Deferring income into an NQDC plan reduces the current year's K-1 income — review brackets and timing before the deadline. See our NQDC Optimizer for the math.
• Charitable contributions. High-income partners benefit significantly from donor-advised funds (DAFs). A $100K contribution to a DAF in a high-income year creates an immediate deduction in the 37% bracket, even if the charitable grants are made over several years. This is particularly powerful in lateral-year or bonus-year income spikes.
• Capital gain and loss harvesting. If you hold a taxable brokerage portfolio, review unrealized positions for harvesting opportunities. Long-term gains above the NIIT threshold cost 23.8% (20% LTCG + 3.8% NIIT). Losses harvested in the same year reduce that exposure dollar-for-dollar.
• AMT projection. Have your CPA run a tentative minimum tax calculation by November — before any year-end moves. ISO exercises, accelerated depreciation, and certain K-1 preference items may flip your AMT exposure.
• Estimated payment true-up. After Q3 distributions are known, reassess your 110% safe harbor calculation and adjust the Q4 estimated payment accordingly. Under-estimating Q4 costs you nothing in penalty if you hit the safe harbor — but a large Q1 surprise is avoidable.

Why a specialist advisor matters for partner-level tax planning

Most CPAs and financial planners encounter law firm K-1s infrequently. The intersection of SE tax on partner ordinary income, §199A SSTB phase-out, multi-state apportionment, quarterly estimated payments on volatile distribution income, and NQDC election timing requires someone who works with this structure regularly. Generalists often miss:

• That the 110% safe harbor applies separately to federal and each state — and that some states don't have safe harbor provisions at all
• That accelerated NQDC deferrals require irrevocable elections before the income is earned, not after the K-1 arrives
• That capital account returns on departure create a different tax treatment than current distributions
• That state sourcing of partnership income can create double-taxation that's only partially offset by resident-state credits

The coordination between your tax return, your financial plan, and your NQDC elections is where specialist expertise pays. A one-time error on an irrevocable 409A election can cost more than an advisor's fee for five years of work.