Prismiva IntelligencePrismivaPortfolio concentration guide
A portfolio can own many stocks and still depend on one company, sector, or economic theme. This plain-English guide shows how to calculate concentration, what the numbers mean, and which questions to ask before changing a position.
Divide a holding's current market value by the total portfolio value. A $25,000 holding in a $100,000 portfolio has a 25% weight, so roughly one quarter of the portfolio's stock-specific result depends on that company before considering correlations.
Sort holdings from largest to smallest and add the first three weights. This exposes portfolios where no single position looks extreme but a few names still dominate. Prismiva's free Portfolio X-Ray calculates this automatically in your browser.
The effective number of holdings is 1 divided by the sum of squared portfolio weights. Ten equally weighted holdings produce an effective count of 10. A 50% position plus five 10% positions produces only about 3.3 effective holdings—even though six ticker symbols appear.
Different tickers can depend on the same customers, rates, commodity, regulation, geography, or technology cycle. Economic concentration may be larger than a sector chart suggests, so group positions by shared drivers as well as formal sectors.
Multiply a position weight by a hypothetical decline to understand its direct portfolio effect before interactions. If a 25% position falls 40%, the direct portfolio impact is about 10 percentage points. This is arithmetic, not a forecast; correlated holdings can change the result.
Earnings, court decisions, regulation, lockups, debt maturities, leverage, dilution, fraud, and forced selling can create risks that volatility alone misses. Check whether several holdings share an event window or whether a position would be difficult to exit.
A concentration finding is a reason to review, not an automatic instruction to sell. Cost basis, holding period, taxes, income needs, time horizon, account type, and alternative exposures all affect the practical decision.
Questions, answered plainly
It is the risk that a small number of holdings or shared economic drivers account for a large part of a portfolio's result. Position weights, top-three weight, effective holdings, sectors, and correlations each reveal a different part of it.
There is no universal safe percentage. The appropriate range depends on risk capacity, time horizon, liquidity, taxes, goals, and the rest of the portfolio. A stated personal limit is more useful than a rule invented after the stock moves.
Convert each position weight to a decimal, square every weight, add the squares, then divide 1 by that sum. The result compares the portfolio's concentration with an equivalent equally weighted portfolio.
Yes. Prismiva's free Portfolio X-Ray runs locally in your browser and calculates largest-position weight, top-three weight, sector exposure, and effective holdings without uploading or saving the entered holdings.