Investing term
What is Concentration risk?
The risk that one position, sector, or country represents enough of the portfolio that a single bad outcome dominates returns.
Concentration risk is the danger that a single position, sector, or country makes up so much of your portfolio that one bad outcome dominates your results. It's the opposite of diversification: when too much rides on one bet, that bet's fate becomes your fate.
It creeps in easily and often invisibly. A single stock that soars can quietly grow into an oversized share of the portfolio; heavy exposure to one hot sector, or to your home country, or to your employer's stock, all concentrate risk without feeling like a deliberate bet. The trouble is that concentration cuts both ways — it magnifies gains, which is why it's tempting, but it also magnifies losses, and a single disaster in a concentrated holding can undo years of careful investing. Watching where your portfolio is concentrated, across holdings, sectors, and geographies, is a core part of managing risk.
Concentration risk is one position, sector, or country making up so much of the portfolio that a single bad outcome drives your results. Winners quietly growing too large is the most common cause.
For example
A tech stock you bought at 5% of your portfolio triples and quietly becomes 20% — now a single bad quarter for that one company can dominate your whole year's return.
Learn it by doing
That's Concentration risk in theory — it clicks when you use it. Practise it hands-on in a free, interactive lesson (Stage 16, Portfolio Construction).
Try the free lesson →Why it matters to you
Concentration risk matters because it's the hidden danger that undoes diversification, often without a deliberate decision. Winners grow into oversized positions, home bias and employer stock pile up exposure, and suddenly one outcome drives everything. Since a single concentrated disaster can erase years of progress, regularly checking where your portfolio is concentrated — and trimming positions that have grown too large — is essential to keeping risk spread rather than piled onto one bet.
⚠ Letting a winner grow unchecked
A successful holding growing into a large share of your portfolio feels like a good problem — but it's concentration risk building silently. The bigger that single position gets, the more your fortunes hinge on it, and the harder a stumble hits. Trimming an overgrown winner back to a sensible weight feels like betting against yourself, but it's the discipline that keeps one holding from dominating your fate.