What is the "Turnover Ratio" of an Index Fund?

When most people think of index funds, they picture a portfolio that simply sits still and mirrors a market index without much activity. This image is largely accurate — index funds do trade far less than actively managed funds. Yet they are not completely static. Every index fund has a turnover ratio, and understanding what drives it can help you evaluate a passive fund more clearly before you invest.

What Does Turnover Ratio Mean?

The turnover ratio of a mutual fund is a measure of how much of the fund's portfolio is replaced over a given period, typically one year. It is expressed as a percentage. A turnover ratio of a certain percentage means that a corresponding portion of the portfolio's holdings were sold and replaced with other securities during that period. A lower ratio generally suggests fewer trades, while a higher ratio suggests more frequent buying and selling.

For actively managed funds, a high turnover ratio is common because fund managers are constantly making decisions about which securities to buy and sell in pursuit of better returns. Index funds, by contrast, are designed to replicate the composition of a specific market index, so their turnover tends to be much lower. However, lower does not mean zero.

Why Does an Index Fund Trade at All?

This is one of the most frequently asked questions by new investors. If an index fund is just copying an index, why would it ever need to buy or sell anything? The answer lies in the fact that an index is not a permanent, unchanging list of companies or securities. Indices are reviewed and updated periodically by index providers, and those updates require the fund to act.

When a company is added to an index, the fund must purchase that security to bring its portfolio in line with the revised index composition. When a company is removed from the index, the fund must sell it. This process, known as index rebalancing or reconstitution, is the primary driver of trading activity in an index fund — and therefore the main contributor to its turnover ratio.

What Triggers Index Reconstitution?

Index reconstitution happens for several reasons. Companies may grow or shrink in market capitalisation, causing them to cross the thresholds that determine inclusion in a particular index. Corporate events such as mergers, acquisitions, delistings, and spin-offs can also change the composition of an index. In some cases, the index provider may change its methodology, resulting in a larger-scale reshuffling of constituents.

Different indices follow different review schedules. Some are reviewed quarterly, others semi-annually or annually. The frequency of these reviews, combined with the pace of corporate changes in the economy, determines how often a given index changes its constituents — and therefore how often the fund tracking it needs to trade.

How Turnover Affects Your Investment

Although index funds have relatively low turnover compared to active funds, even a modest level of trading activity has implications for investors.

First, there are transaction costs. Every time a fund buys or sells a security, it incurs brokerage charges and may also face market impact costs, particularly when trading large volumes. These costs are borne by the fund and ultimately affect the returns delivered to investors. A fund with unnecessarily high turnover may underperform its benchmark by a wider margin over time, even if the manager is not making active bets.

Second, there is tracking error. The more a fund trades, the greater the possibility that its portfolio will temporarily diverge from the index it is meant to replicate. Well-managed index funds try to execute reconstitution trades efficiently to keep tracking error as low as possible, but some degree of deviation is inevitable.

Third, in certain tax jurisdictions, trading activity within a fund can have tax implications for investors depending on how gains and losses are treated. It is always advisable to understand the tax rules applicable to your investments.

How Index Fund Managers Handle Rebalancing

Experienced index fund managers are aware that reconstitution events can move markets. When it becomes publicly known that a particular security will be added to or removed from a major index, other market participants often try to trade ahead of the fund, which can push prices in an unfavourable direction. To manage this, fund managers may use a variety of strategies to time their trades more effectively and reduce the cost of rebalancing.

Some funds also receive fresh money from investors on an ongoing basis through systematic investment plans and new lump-sum purchases. Managers can sometimes use these inflows to gradually adjust the portfolio toward the new index composition rather than making large, sudden trades. This approach can help contain turnover and reduce associated costs.

Comparing Turnover Ratios Across Index Funds

Not all index funds tracking the same index will have exactly the same turnover ratio. Differences in how each fund handles cash flows, dividend reinvestment, and reconstitution trades can lead to variation. When comparing index funds, the turnover ratio is one useful data point alongside expense ratio, tracking error, and the size of the fund's assets under management.

A fund with a lower turnover ratio is generally more cost-efficient, all else being equal. However, you should also check whether the lower turnover is accompanied by a higher tracking error, which might indicate that the fund is not faithfully following its benchmark.

What Should an Investor Take Away?

The turnover ratio is not a measure that investors spend a great deal of time discussing, but it is a meaningful indicator of how efficiently an index fund is managed. Understanding that even passive funds trade — and why they do — helps you set realistic expectations. An index fund will never have zero turnover as long as the index it tracks continues to evolve. The goal is not to eliminate trading but to keep it purposeful, efficient, and aligned with the index's own changes.

When you evaluate index funds on Stashfin, you can review key fund details to understand how each option compares. Taking the time to look beyond just the expense ratio and examining factors like turnover ratio and tracking difference can help you make a more informed choice for your long-term financial goals.

Mutual fund investments are subject to market risks. Past performance is not an indicator of future returns. Please read all scheme-related documents carefully before investing.