Concentration risk
What is Concentration risk?
Concentration risk is the possibility that a large exposure to one issuer, sector, geography, currency, counterparty, or common factor causes disproportionate portfolio loss.
Why concentration risk matters
Portfolio losses are driven by the exposures that matter most, not by the number of line items. Several funds and securities can depend on the same companies or economic outcome. Concentration can be intentional in a high-conviction strategy, but it should be visible, sized deliberately, and consistent with the investor's ability to withstand permanent loss.
How it is measured
Measures include largest and top-ten weights, sector and country shares, the Herfindahl-Hirschman Index, issuer-group exposure, and marginal risk contribution. Look-through analysis consolidates underlying holdings, while factor models identify shared systematic drivers. Stress tests estimate losses when the concentrated exposure and related positions move together under adverse conditions.
Example
A portfolio holds five technology funds plus direct shares in several large platform companies. Each line is below a 5% limit, but look-through aggregation reveals a 17% exposure to one issuer and a much larger growth-factor exposure. A company event or rate shock could therefore cause a loss far greater than line-item weights suggest.
How to interpret it
Compare concentration with mandate limits, benchmark structure, liquidity, and the evidence supporting the position. A benchmark-heavy holding may still create absolute risk, while an active underweight can create benchmark-relative risk. Review capital and risk concentration together because a volatile small position can contribute more risk than a larger stable one.
Limitations
Weight-based measures miss correlation, derivatives, options, and changing volatility. Factor models can omit the true common driver, and published fund holdings may be delayed. Reducing one visible position may not reduce total risk if proceeds are moved into a close substitute. Concentration analysis therefore requires several classifications and scenarios.
Practical checklist
Aggregate direct, derivative, and fund exposures by issuer group, sector, country, currency, counterparty, and factor. Review top weights and stressed losses at both portfolio and sleeve level. Document the rationale, maximum size, liquidity, and exit conditions for intentional concentrations. Set alerts for appreciation-driven breaches and ensure diversification trades reduce the underlying driver rather than only the label.