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What is portfolio concentration risk and how do Indian investors manage it?
What is portfolio concentration risk: how single-stock, sector, and thematic concentration creates vulnerability, how to measure it, and practical diversification approaches for the Indian retail investor.
In one line
Portfolio concentration risk is the risk that a portfolio's returns are dominated by a small number of holdings or a single sector, such that an adverse event in that concentrated area causes disproportionate portfolio damage.
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Three types of concentration risk
Single-stock concentration: when one holding accounts for more than 15 to 20 percent of portfolio value, that stock's performance dominates portfolio outcomes. If the stock falls 40 percent, a 20 percent portfolio weight means an 8 percent portfolio loss from that one position alone. Beginners often concentrate inadvertently by investing heavily in the few stocks they know best.
Sector concentration: a portfolio of 15 stocks can still be highly concentrated if 10 of them are banking and financial stocks. When the banking sector corrects, all 10 fall simultaneously, providing little diversification benefit despite the number of holdings. True diversification requires positions in different sectors with different underlying drivers.
Thematic concentration: sometimes less obvious than sector concentration. A portfolio with positions in railways, construction, cement, and capital goods stocks looks diversified across sectors but is actually all exposed to the same government infrastructure capex theme. If the infrastructure spending cycle slows, all these positions underperform together.
Measuring concentration
The Herfindahl-Hirschman Index (HHI) is a formal measure of concentration: sum the squares of each holding's portfolio weight. An HHI of 10,000 (all in one stock at 100 percent) is maximally concentrated; an HHI below 500 is relatively diversified. Most retail investors do not use HHI formally but the concept of summing the squares intuitively captures how concentration risk scales non-linearly with position size.
A simpler practical test: what would happen to your portfolio if your largest holding fell 50 percent? What if the banking sector fell 30 percent? These stress tests reveal concentration exposures more viscerally than abstract numbers.
Managing concentration without eliminating conviction
The goal of concentration management is not to achieve perfect diversification across 50 holdings -- too many holdings dilute returns and are impossible to monitor. The typical guidance is 15 to 25 stocks across at least 6 to 8 different sectors for a focused portfolio. Position sizing should reflect conviction: a high-conviction holding at 8 to 10 percent is reasonable; a maximum single-stock weight of 15 percent is a sensible ceiling for most retail investors.
Sector limits are equally important. Allocating more than 25 to 30 percent to any single sector (including banking and financial services, which is the most common overweight among Indian retail investors) creates exposure to sector-level events. Setting explicit per-sector allocation caps and reviewing them annually helps prevent inadvertent drift into concentration.
FAQ2 reader questions · AEO-eligible
Common questions on what is portfolio concentration risk.
How many stocks do I need for a diversified portfolio?
Research suggests that most of the benefits of diversification are achieved with 20 to 25 stocks spread across different sectors. Beyond 30 stocks, the marginal diversification benefit decreases while the monitoring burden increases. For a focused investor, 15 to 20 stocks across 6 to 8 sectors is typically a workable concentrated-but-not-reckless portfolio. The key is sector and thematic diversification, not just the count.
Is too much diversification also a problem?
Yes. Over-diversification (holding 40 to 50 or more stocks) dilutes the positive impact of your best ideas and creates a portfolio that effectively mirrors an index while paying stock-picking attention costs. If a position is too small to move the needle, the research time spent on it is wasted. Charlie Munger described over-diversification as 'di-worsification'. A focused portfolio of well-understood businesses is superior to a holding-zoo of superficially familiar names.
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