Portfolio Monitoring
What is concentration risk in a portfolio?
Answer
Concentration risk is the risk created when a large share of a portfolio depends on the same thing — one company, one sector, one factor, or one fund house. It matters because the loss from a single adverse event is proportional to the weight exposed to it, and because concentration usually accumulates through ordinary decisions rather than being chosen.
The four levels concentration occurs at
A portfolio can be diversified at one level and concentrated at another, which is why a single diversification score is misleading.
- Single company. The look-through weight of one business, counting direct holdings and every fund that holds it.
- Sector. Indian equity portfolios commonly carry a financials weight far above what the investor would choose deliberately, because financials are a large share of every broad index.
- Factor. Several funds selected on similar criteria — quality, momentum, large-cap growth — behave like one position when that factor turns.
- Fund house. Operational rather than market risk, but real: several schemes from one AMC share a house view, a research process and, in a credit event, a set of counterparties.
How concentration accumulates
Almost never by decision. An employee accumulates company stock through ESOPs until it is a third of their net worth. A holding that performed well becomes a large weight simply by appreciating. Four funds bought over eight years each hold the same five large companies near the top of their portfolios. Every one of those is a reasonable step, and the result is a portfolio nobody designed.
This is why concentration is a measurement problem before it is a decision problem: an investor cannot act on an exposure they cannot see, and none of the four levels above is visible from a list of fund names and current values.
How concentration is measured
Three measures, each answering a different question.
Top-N weight. The share of the portfolio in its largest N look-through holdings, usually five or ten. The most directly interpretable: it is the share of the portfolio that depends on ten decisions.
Largest single weight. The one number that governs the worst single-name outcome.
Herfindahl-Hirschman Index (HHI). The sum of every holding's squared weight. Useful because it captures the whole distribution rather than an arbitrary cut-off, and because squaring means one large position moves it far more than several small ones. A portfolio of twenty equal positions has an HHI of 0.05; one where a single holding is 40% has an HHI above 0.16 however many small holdings sit beside it.
When concentration is a decision rather than a risk
Concentration is not automatically a defect. An investor who has researched a business and deliberately sized a position at 15% has taken a considered risk. The same 15% arrived at by appreciation and never revisited is an unexamined one.
The distinction is whether the weight is intended. A finding that reports "this position is 15% of your portfolio" is useful to both investors; a system that insists 15% is wrong is useful to neither.
How Vestmind measures concentration
VestFolio computes look-through weights across direct holdings and every fund, then measures concentration at company, sector, factor and fund-house level, reporting top-N weight, the largest single exposure and HHI. Each finding names the holdings that produced it, so an intended position can be recognised as one. See the portfolio risk methodology.
Related questions
What is a safe single-stock weight?
There is no regulatory or universal answer, and the honest framing is a question rather than a limit: how much of this portfolio can lose most of its value without the plan failing. For an investor whose goals are funded by this portfolio alone, a single company above roughly 10% of it is usually worth a deliberate decision rather than an accident. For someone with income elsewhere and a long horizon, a larger deliberate position can be reasonable. What matters is that the weight was chosen.
Does holding many stocks mean I am diversified?
No. Diversification depends on weights and on what the holdings have in common, not on the count. Fifty positions where the top five are 60% of the portfolio is a concentrated portfolio with a long tail. Fifty positions all in one sector is a sector bet held fifty ways.
Is sector concentration worse than stock concentration?
Different rather than worse. Single-stock concentration exposes a portfolio to events at one company — fraud, a failed product, a regulatory action — which are idiosyncratic and can be total. Sector concentration exposes it to events affecting an entire industry, which are usually less severe per holding but affect everything at once, so they cannot be diversified away within the sector.
How do I reduce concentration without a tax bill?
Direct new contributions away from the concentrated exposure rather than selling it. This changes weights over time with no capital gains event. Where selling is necessary, staging it across financial years and harvesting losses elsewhere in the portfolio reduces the cost. Selling everything at once to reach a target allocation is usually the most expensive route to it.
Sources
- National Stock Exchange of India — listed company disclosures and index constituents
- Securities and Exchange Board of India (SEBI)
How Vestmind does this
VestFolio is Vestmind's AI portfolio analysis product. It reads an Indian investor's holdings — stocks, mutual funds and ETFs — and reports what the portfolio is actually exposed to: concentration, mutual fund overlap, sector and factor tilts, asset allocation drift and the risks those create.