Single Stock Concentration Risk 2027 Calculator
Enter your total portfolio and the value of one stock holding. The calculator shows what share of the portfolio that stock represents, how much you would need to move out of it to bring it down to 10%, and how much you would lose if the stock fell by 50% or 80%. It is plain arithmetic on your own numbers — no market data or forecasts. The 10% figure is a common rule of thumb used here as an illustration, not a regulatory limit.
What the Numbers Mean
Concentration = single stock holding ÷ total portfolio. Example: a $800,000 holding in a $2,500,000 portfolio is 32.0%. To bring it down to 10% of the same total you would move $800,000 − 10% × $2,500,000 = $550,000 into other investments.
Why Concentration Matters
The larger one holding is, the more the whole portfolio depends on a single company. If that $800,000 holding fell by half, the portfolio would lose $400,000, which is 16.0% of its value, however the rest performed. People who are paid partly in employer shares often build up a large position without choosing to.
Things the Calculator Leaves Out
Selling shares can trigger capital gains tax, which reduces what you can reinvest. Vesting schedules, trading windows and lock-ups may limit when you can sell. The right target weighting depends on your circumstances — 10% is used here only as a round illustration.
Source and Disclaimer
This page uses no external statistics: every result is calculated from the two figures you enter. It is not investment advice.
Method: arithmetic on your own inputs; no market data is used. Last updated: October 2026.