Largest holding weight
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Calculator · Investing
Position concentration calculator
List up to eight holdings with their market value and sector. The position concentration calculator weighs each one, finds the largest holding and the largest sector, and shows what a fall of your choosing in the biggest position would cost the whole portfolio.
Largest sector weight
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Portfolio loss if it falls
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Loss as % of portfolio
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The working
What the weights tell you
A holding's weight is its market value divided by the value of everything in the portfolio. Sector weight adds up the holdings that share a label. The loss figure multiplies the largest holding's weight by the fall you enter, which is the whole of the damage if nothing else moves: a 30% position that halves costs 15% of the portfolio. Weight times a plausible fall turns a percentage into dollars. It also lets you set a cap from the loss you could stand. How much of a portfolio one stock should be works through that backward sum in more detail, and the lesson on setting a weight cap turns it into a rule.
A worked example on the defaults
A hypothetical $100,000 portfolio holds six stocks. Stock A is worth $30,000, or 30.00% of the total, and Stock B another $20,000. Both carry a Technology label, so that sector comes to 50.00%. The other four stocks, in health care, financials, energy and consumer staples, share the remaining half. Suppose Stock A falls by half. The portfolio loses $15,000, or 15.00% of its value. One position did that. Stocks A and B also share a sector, and a bad stretch for technology can hit both at once, so your exposure to a single theme sits nearer the 50% sector figure than the 30% on the largest line.
Where the figures mislead
Funds hide concentration. A broad fund entered as one line looks spread out, yet its largest holdings can be the same companies you already own directly, which is the argument in your index fund has a concentration problem too. Check the fund's holdings page for its top positions and sector split, and add them to the stocks you hold outright if you want the combined picture. Sector labels are coarse. Two stocks in different sectors can still depend on the same customer or the same interest rate. Weights also drift: a winner grows its own share of the portfolio every month it keeps rising, so re-run the numbers after big moves. Build it, then break it lets you stress a portfolio like this one against moves made up for the game.
Questions about this calculator
What percentage of a portfolio should one stock be?
There is no rule that fits every account. Work backward from the loss you could live with: if a 50% fall in one stock should cost the whole portfolio no more than 10%, that stock can be at most 20% of it. You might then pick a cap below that figure and trim whenever a winner grows past it.
Should funds count as one holding or many?
Count a fund as its own line, then look inside it. A broad index fund spreads its value across hundreds of companies, so a 30% weight in one is a different risk from 30% in a single stock. Its largest holdings may overlap with stocks you own directly, which adds to your real exposure to those companies and their sector.
How do I get sector labels for my holdings?
Most quote pages list a sector and an industry for each stock, usually taken from a published classification such as GICS. Use the same source for every holding so the labels match, and spell them the same way in the calculator, since sectors are grouped by name. Case does not matter.
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