Planning tool

Employer stock concentration calculator.

If you hold a concentrated position in employer stock, this calculator shows how much you would need to sell under a 10b5-1 plan to reach a target concentration level, and gives a federal tax estimate on that sale. Enter your position, income, and target — results appear instantly.

Example: A VP at a public company holds $2.5M of employer stock in a $5M portfolio (50% concentration). She wants to reduce to 15%. The calculator shows her she would need to sell roughly $2.06M — then estimates the federal LTCG and NIIT on that sale so she can build a tax reserve before the plan's first trade date.

Your situation

Employer stock value ($)

Total investable assets ($) — including employer stock

Cost basis of employer stock ($)

Target concentration after plan (%)

Other ordinary income this year ($) — salary, bonus, RSU vest

Filing status

Estimated results

Item	Amount
Current employer-stock concentration	—
Target concentration	—
Employer stock to sell	—
Long-term capital gain on sale	—
Federal LTCG tax (2026 brackets)	—
Net Investment Income Tax — 3.8%	—
Total estimated federal tax	—
After-tax proceeds	—
Effective federal rate on sale	—
Employer-stock concentration after sale	—

Federal only. State income tax, AMT, prior-year loss carryforwards, deductions, and lot-selection optimizations are excluded. All sale proceeds treated as long-term capital gain. Actual tax depends on your full Form 1040, broker lot selection, and plan-year stacking. Post-sale concentration assumes sale proceeds leave the employer-stock position; reinvested after-tax proceeds reduce concentration further.

What this calculator shows — and what it misses

Concentration mathSolves for the exact sale amount that brings employer stock from its current share of your portfolio to your target, assuming proceeds exit the position.

Federal LTCG + NIITApplies 2026 0/15/20% brackets stacked on top of ordinary income, plus the 3.8% NIIT surtax above $200K (single) or $250K (MFJ).¹²

State tax — not includedCalifornia, New York, and Minnesota tax capital gains as ordinary income. A $2M sale in California can add $220,000+ in state tax. Enter your position with an advisor before counting on the after-tax proceeds estimate.

Lot selection — not includedSelling high-basis lots first, harvesting embedded losses, or holding shares until a long-term holding period triggers can move the effective rate by 3–8 points on a large position.

Short-term gains: RSU shares that vest within the last 12 months, ESPP shares with a disqualifying disposition, or NQ option shares held less than a year are taxed at ordinary income rates, not the LTCG rates used here. If your position includes recent vests or option exercises, the calculator will understate the tax bill.

Key rules that interact with the sale

A 10b5-1 plan sets the when — the compliance structure that lets you trade despite blackout windows and MNPI access. The financial work is deciding how much to sell, from which lots, in which tax year, and how the proceeds fit the rest of your plan.

Cooling-off period: Directors and officers generally cannot trade until 90 days after plan adoption, or two business days after the company's earnings release for the quarter of adoption — whichever is later, up to 120 days.³ The calculator assumes you are planning forward from an adoption date, not that a trade can happen immediately.
Single-plan rule: The SEC 2022 amendments generally prohibit having more than one single-counterparty 10b5-1 plan at a time (with limited exceptions). If you are trying to layer a second plan on top of a first, the structure needs counsel review before any financial modeling.
Rule 144 volume limits: Affiliates selling restricted or control securities are subject to Rule 144 volume caps (the greater of 1% of outstanding shares or the average weekly volume for the prior four weeks). Large positions may not be fully saleable within one plan year even if the tax modeling supports it.
Section 16 reporting: Directors and officers report dispositions on Form 4 within two business days of the trade date.
IRMAA lookback: For executives within two years of Medicare eligibility, a large sale in a single tax year can raise Medicare Part B and D premiums for the following two years. 2026 IRMAA surcharges start at AGI above $106,000 (single) or $212,000 (MFJ).⁴

For the full compliance picture, see 10b5-1 plan rules, cooling-off period guide, and the pre-adoption checklist.

Model this for your actual position

The calculator above gives a federal planning estimate. An advisor who specializes in executive equity can model state tax, lot-level strategy, RSU stacking, IRMAA exposure, charitable structures, and plan-timing tradeoffs — often finding material savings on a $1M+ position.

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Sources

IRS, Topic No. 559: Net Investment Income Tax — 3.8% NIIT threshold: $200,000 single, $250,000 MFJ; not indexed for inflation.
Kiplinger, IRS Updates Capital Gains Tax Thresholds for 2026 — 2026 LTCG brackets: 0% to $49,450 single / $98,900 MFJ; 15% to $545,500 single / $613,700 MFJ; 20% above those thresholds.
SEC, Release 33-11138 (Dec 2022) — amended Rule 10b5-1 cooling-off periods, single-plan limit, and certification requirements for directors and officers.
CMS / Medicare, Medicare Costs at a Glance 2026 — IRMAA surcharge tiers, Part B base premium, and income thresholds for Medicare-eligible executives.

Federal tax values verified as of May 2026. State taxes and AMT not reflected. Verify current-year values before finalizing any plan.