For Indian investors moving into index funds and ETFs, one number may distinguish between a well-run fund from a poorly managed one: tracking error. While most investors focus on expense ratio and past returns, tracking error tells you how a fund actually mirrors its benchmark, such as the Nifty 50 or Sensex. A fund with a low expense ratio can still disappoint if it fails to replicate the index efficiently. As passive investing gains ground in India understanding tracking error has become essential for anyone choosing between similar index funds or ETFs.
What is Tracking Error?
Tracking error represents the degree to which a fund's returns vary from those of an index over a period of time. Tracking error arises from differences between a fund's returns and its benchmark due to factors such as expense ratio, cash holdings, transaction costs, portfolio rebalancing, and replication methodology, rather than intentional stock selection in passive funds.
Why Does Tracking Error Matter?
Tracking error is one of the most reliable indicators of how skilfully an Asset Management Company (AMC) runs a passive fund. It matters because:
- It reveals execution quality, how well the fund manager buys and sells stocks during rebalancing.
- It helps compare two funds tracking the same index, even if their expense ratios look similar.
- It works as a risk-assessment tool, offering insight into the consistency of returns relative to the benchmark.
- Investors seeking passive exposure generally prefer funds with lower tracking error because the fund is more likely to replicate the benchmark consistently.
- SEBI mandates disclosure, so it also reflects regulatory compliance and transparency.
How Is Tracking Error Calculated?
Tracking Error Formula:
The SEBI Investor Education portal describes two commonly used approaches:
Simple deviation: Tracking Error = Return (Portfolio) − Return (Index)
Standard deviation method: Tracking Error = Standard Deviation of (Portfolio returns − Benchmark returns)
In practice, Indian AMCs use the standard deviation method, calculated as the annualised standard deviation of the difference in daily returns between the underlying index and the NAV of the ETF or index fund, based on rolling one-year data.
Understanding the Formula
The formula essentially captures volatility of the gap, not just the average gap. Two funds could have the same average deviation from the index, but the one whose daily deviations swing more widely has a higher tracking error, and therefore less predictable behaviour relative to the benchmark.
Tracking Error Calculation: Worked Example
Suppose a Nifty 50 index fund's daily return differs from the index's daily return as follows over five trading days:
Day | Fund Return (%) | Index Return (%) | Difference (%) |
1 | 0.52 | 0.55 | -0.03 |
2 | -0.30 | -0.28 | -0.02 |
3 | 0.71 | 0.70 | +0.01 |
4 | -0.15 | -0.12 | -0.03 |
5 | 0.40 | 0.42 | -0.02 |
Calculation of standard deviation of the daily discrepancies and annualisation thereof (multiplying the value by the square root of 252 business days) results in calculation of the fund’s tracking error. In actual Indian market data, this number turns out to be very low indeed – for example, one large cap Nifty 50 fund had a tracking error of only 0.07%, while a factor index fund had a tracking error of 0.06% and sectoral index fund had tracking error of only 0.01%.
What Factors Affect Tracking Error?
Several operational elements push tracking error up or down:
- Cash drag: Mutual funds must hold some cash to handle investor redemptions, and when markets rise, this cash earns far less than equities, dragging fund returns below the benchmark.
- Expense ratio: Higher recurring costs widen the gap versus the index.
- Rebalancing lag: Delays in adjusting the portfolio when the index changes its constituents.
- Fund size and redemption patterns: Larger, more stable funds with lower redemption pressure tend to manage this drag better.
- Corporate actions: Dividends, bonuses, and stock splits that are not immediately reflected in the portfolio.
Tracking Error in ETFs and Index Funds
Although both instruments aim to replicate an index, ETFs face an additional layer of complexity because an ETF's price moves during the trading day like a stock, and its value is based on the NAV of the underlying assets. SEBI's 2026 review of ETF base price and price bands aims to bring the pricing of ETFs closer to their underlying assets and improve price discovery, but this does not eliminate tracking error, since it is largely driven by fund management, not exchange mechanics. Index mutual funds, by contrast, transact at end-of-day NAV, which makes them predictable in execution and well-suited to SIPs.
Tracking Error in Active vs Passive Investing
In active investing, deviation from the benchmark is intentional, fund managers try to outperform the index, and tracking error is sometimes called "active risk" in this context. In passive investing, the goal is the opposite: to match the benchmark as closely as possible. Therefore, a high tracking error in an active fund may simply reflect an aggressive strategy, but in a passive fund, it points to poor replication or operational weakness.
Limitations of Tracking Error
Despite many benefits, tracking error still has certain limitations that include:
- It does not explain why the deviation occurred — only that it did.
- SEBI does not prescribe a fixed "acceptable" tracking error range, leaving interpretation partly subjective.
- It can be confused with tracking difference, a related but distinct measure.
- Short-term tracking error figures can be misleading; consistency over multiple years matters more than a single reading.
Conclusion
Tracking error is a good indicator of how well an index fund or ETF does its one job: mirroring its benchmark. With India's SEBI (Mutual Funds) Regulations, effective from April 2026, having lowered the base expense ratio cap for index funds and ETFs from 1.00% to 0.90%, structural costs are shrinking industry-wide — making tracking error an even sharper differentiator between well-run and poorly-run passive funds. Before investing, always check a fund's tracking error alongside its expense ratio and AUM.
FAQs on Tracking Error
What is tracking error in mutual funds?
It is the extent to which a mutual fund's returns deviate from its benchmark index, usually expressed as an annualised percentage.
What is the tracking error formula?
Tracking Error = Standard Deviation of (Portfolio returns − Benchmark returns), calculated from daily return differences and annualised.
What does a low tracking error indicate?
It suggests the portfolio closely follows the benchmark, reflecting efficient fund management.
What are the main sources of tracking error?
Cash drag, expense ratio, rebalancing lag, corporate action delays, and fund size.
Is a lower tracking error always better?
Generally yes, but consistency across years matters more than a single low reading.
How is tracking error different from tracking difference?
Tracking difference is the difference between the returns generated by the fund and its benchmark over a period, while tracking error measures the volatility of that gap daily.
How is tracking error calculated?
By taking the annualised standard deviation of the difference in daily returns between the index and the fund's NAV, typically using one-year rolling data.
What is a good tracking error for an index fund?
There's no official benchmark, but SEBI caps tracking error for equity ETFs and index funds at 2%; and well-managed large-cap funds in India often report figures well below 0.10%.
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