5.3.4 Diversification Limits

The two failure modes

Holding a single fund, or a small handful of very similar ones, leaves a portfolio exposed if that specific strategy or fund manager has a genuinely bad stretch. At the other extreme, holding fifteen or twenty funds across similar categories often just means each fund quietly holds many of the same large, well-known stocks as the others, adding paperwork and complexity without adding any genuine diversification benefit.

Diversification reduces risk by spreading investments across multiple securities, sectors, asset classes and geographies so that a loss in one is offset by stability or gains in others. However, diversification has diminishing returns: the first few additions to a concentrated portfolio produce large risk reductions, but beyond a certain point, adding more holdings provides negligible additional benefit and can actually increase costs and complexity.

Why more funds does not automatically mean more diversification

Diversification comes from combining assets that behave differently from each other, not simply from owning a larger number of them. Two large cap funds from different AMCs likely hold significant overlap in their top ten or twenty positions, since both are drawing from a similar universe of large, well-established companies, meaning a fifth or sixth large cap fund adds little that the first one did not already provide.

Research shows that approximately 80-90% of the risk reduction from equity diversification is achieved with 25-30 stocks spread across sectors. Moving from 30 to 100 stocks adds marginal risk reduction while increasing the likelihood of holding mediocre companies and complicating portfolio management. For mutual fund investors, a similar principle applies: holding 3-5 equity funds across different categories (large-cap, mid-cap, international) provides adequate diversification. Holding 15-20 funds creates excessive overlap, makes rebalancing impractical, and guarantees that the overall portfolio converges toward the market return minus higher aggregate costs.

A practical guideline

A reasonable starting point is somewhere between four and eight carefully chosen funds spanning genuinely different categories and asset classes, rather than judging sufficiency purely by the total count of funds held. Checking overlap directly, rather than assuming that more funds automatically means safer, more thorough diversification, is the more reliable approach.