Concentration risk
Concentration risk is the danger of losing heavily because too much of your money sits in one holding. If that one bet goes wrong, the loss is large. Spreading money across several holdings reduces it, but owning so many that you cannot explain them hides risk instead of removing it.
The old rule
Do not put all your money in one stock, because if that one turns out wrong, you lose too much. That is concentration risk: the danger of being exposed to a single bad outcome. Spreading across several stocks and funds is the sound answer, and the name for it is diversification.
The opposite failure
Spreading has a second edge. Once you own so many things that you can no longer say why you hold each one, you have not removed risk, you have only hidden it. This is over-diversification: too many holdings to track or understand, each one a small blind spot.
Both are the same failure
Too few holdings, and one wrong call can hurt you badly. Too many, and you stop knowing what you own. Both are money placed somewhere you cannot account for. There is no fixed count that marks the safe middle.
A one-sentence test
What matters is whether you can state, in one sentence, why each holding is in your portfolio. If you can, it earned its place. If you cannot, adding it did not protect you. Ask for that sentence before you buy anything new.
How concentration shows up (hypothetical numbers)
Suppose 60 percent of your portfolio is in one stock and it falls 30 percent. Your portfolio falls about 18 percent from that one holding alone. If the same money were spread equally across 10 holdings and one fell 30 percent, the portfolio would fall about 3 percent.
Now suppose you list your 18 holdings and write one sentence for each. You can do it clearly for only 4. You sell nothing yet, but you mark the other 14 to study or drop before buying anything new.
Common questions
- What is concentration risk?
- The danger of losing heavily because too much money is in one holding.
- How many stocks should I hold?
- There is no fixed number. The useful test is whether you can say in one sentence why each holding is there.
- Is owning many holdings always safer?
- No. Too many holdings can mean you no longer know what you own, which is its own hidden exposure.
- Does diversification remove all risk?
- No. It limits how much one wrong bet can cost you. A bad year that hits many things at once can still pull a spread portfolio down.