Tracking difference in index funds
Tracking difference is the cumulative return of an index fund’s benchmark minus the fund’s cumulative return over a specified period, expressed in percentage points. Unlike tracking error (the standard deviation of periodic return differences), tracking difference is a single signed number that directly measures the magnitude of the fund’s under- or over-performance relative to its benchmark over the full measurement period.
Tracking difference is arguably the more investor-relevant metric for cost comparison among passive funds: it shows the actual wealth impact of owning the fund relative to the benchmark, not just the volatility of daily deviations.
Formula
\[ \text{Tracking difference (TD)} = R_{\text{benchmark}} - R_{\text{fund}} \]
Where both returns are cumulative (total returns) over the same period, calculated from the benchmark total return index (TRI).
A positive tracking difference means the benchmark outperformed the fund, the investor lost return relative to a theoretical index exposure. A negative tracking difference (rare) means the fund outperformed the benchmark, which can occur due to securities lending income or superior dividend handling.
Worked example
Over a 12-month period:
- Nifty 50 TRI return: 14.80%
- Index fund NAV return: 14.63%
\[ \text{TD} = 14.80 - 14.63 = +0.17% \]
The fund underperformed the TRI by 17 basis points. For a fund with TER of 0.15 per cent, this implies approximately 2 basis points of additional drag from cash management, dividend reinvestment timing, or rebalancing costs.
Tracking difference vs tracking error
| Dimension | Tracking difference | Tracking error |
|---|---|---|
| What it measures | Cumulative return gap (fund vs benchmark) | Standard deviation of periodic return gaps |
| Sign | Signed (positive = underperformance, negative = outperformance) | Always positive |
| Period | Single cumulative value over the measurement window | Requires multiple periods |
| Investor relevance | Direct cost of owning fund vs index | Consistency of replication |
| Best use | Comparing total cost of passive funds | Assessing replication quality for institutional mandates |
Both metrics are needed for a full evaluation: a fund can have low tracking error (consistent deviations) but a high tracking difference (consistently underperforming), or vice versa.
Components of tracking difference
1. Total expense ratio
The TER is the largest contributor to tracking difference in a well-managed fund. A fund charging 0.20 per cent TER should have tracking difference close to 0.20 per cent per year, absent other factors. The relationship is approximately:
\[ \text{TD}_{\text{expected}} \approx \text{TER} - \text{Securities lending income} + \text{Cash drag} + \text{Rebalancing slippage} \]
2. Securities lending income
ETFs and some index funds lend portfolio securities to short-sellers, earning lending fees that partially or fully offset TER. Large liquid ETFs (particularly Nifty 50 ETFs from major AMCs) have reduced their effective tracking difference to below TER through lending income. Some ETFs have achieved negative tracking difference (outperformed the index) in periods of high lending demand.
3. Dividend reinvestment timing
The TRI assumes instantaneous dividend reinvestment at the ex-date NAV. In practice, dividends are received 1–2 days after the record date and must be reinvested at the subsequent day’s price. In volatile markets, this delay can cause a small but non-trivial tracking difference contribution.
4. Cash drag
Index funds hold a cash buffer for redemptions. Cash earns a lower return than equity, creating negative contribution to fund return. Skilled cash management (using overnight funds or liquid securities for the buffer) reduces this drag.
5. Index rebalancing costs
When NSE or BSE reconstitutes an index (quarterly for most), the fund must execute trades to match the new composition. Market impact costs on these trades (particularly for mid and small-cap indices) increase tracking difference. Large funds trading in illiquid stocks face proportionally higher impact costs.
Typical tracking difference in Indian passive funds (2023–2024)
| Fund type | Typical annual tracking difference |
|---|---|
| Nifty 50 ETF (top-3 by AUM) | 0.02–0.08% |
| Nifty 50 index fund | 0.08–0.20% |
| Nifty Next 50 index fund | 0.12–0.30% |
| Nifty Midcap 150 index fund | 0.20–0.50% |
| Nifty Smallcap 250 index fund | 0.30–0.80% |
| International fund of funds | 0.50–1.50% |
| Gold ETF | 0.10–0.35% |
Nifty 50 ETFs have very low tracking difference because their TERs are minimal (0.05–0.10 per cent), securities lending generates income, and the Nifty 50 components are highly liquid with negligible rebalancing impact.
Smallcap index funds have higher tracking difference due to liquidity constraints and rebalancing costs in the underlying stocks.
SEBI’s total return index mandate and its effect on tracking difference measurement
SEBI circular SEBI/HO/IMD/DF2/CIR/P/2018/007 (January 2018) mandated that all mutual fund schemes benchmark against the total return index (TRI). Before this, funds were benchmarked against price-return indices (which exclude dividends), artificially reducing the apparent tracking difference by the dividend yield of the index (approximately 1.0–1.5 per cent for Nifty 50 per year).
Post-2018, tracking difference measurement is accurate: both fund and benchmark are on a total-return basis, and the dividend component is no longer a free source of apparent outperformance.
Tracking difference for fund selection
When choosing between index funds tracking the same benchmark:
- Compare 1-year, 3-year, and 5-year tracking differences, consistency matters more than a single good year.
- Prefer funds where tracking difference is close to or below TER, funds with tracking difference materially above TER have hidden inefficiencies.
- Consider AUM: larger funds have better operational efficiency (lower per-unit transaction costs, better lending terms) and typically lower tracking difference.
- Check the trajectory: improving tracking difference over time (fund moving closer to the index) indicates operational improvements; worsening trajectory warrants scrutiny.
Relationship to TER
TER is the visible, disclosed cost. Tracking difference is the actual cost, incorporating all factors. The spread between tracking difference and TER is an important diagnostic:
- TD = TER: Ideal, no hidden costs beyond the declared TER.
- TD > TER: Cash drag, impact costs, or operational inefficiencies add to costs beyond TER.
- TD < TER: Securities lending income or other sources partially offset TER, the fund is generating additional income.
See also
- Tracking error in index funds
- Total return index benchmarking
- Total expense ratio in mutual funds
- Portfolio turnover ratio
- Information ratio
- Mutual fund
- SEBI
References
- SEBI circular SEBI/HO/IMD/DF2/CIR/P/2018/007 dated 4 January 2018, TRI benchmarking mandate.
- NSE Indices, Nifty 50 TRI methodology, niftyindices.com.
- AMFI, Index fund and ETF tracking difference data, amfiindia.com.
- Value Research, Tracking difference database for Indian passive funds, valueresearchonline.com.
- ETF.com, Tracking difference methodology (US reference), etf.com.