Investor Corner/Building and judging a portfolio/Performance Measurement
3.2.5 Tracking Error
Tracking error measures how much an index fund or ETF's returns deviate from the index it is meant to replicate. A lower tracking error means the fund is doing a genuinely better job of matching its target.
What causes a fund to drift from its index
An index fund should aim to move almost identically to its target index, but small differences creep in from the fund's own expense ratio, the cash it must hold temporarily to manage investor inflows and redemptions, and minor timing gaps between when the index itself rebalances and when the fund actually trades to match that change.
Tracking error measures how closely a fund's returns follow its benchmark index. It is calculated as the standard deviation of the difference between the fund's returns and the benchmark's returns over a period. A tracking error of 0.5% means the fund's returns deviate from the benchmark by about half a percentage point in a typical period. For an index fund, lower tracking error is unambiguously better; for an active fund, some tracking error is expected and reflects the manager's active bets.
Why this matters specifically for passive funds
The entire appeal of an index fund rests on it reliably delivering the index's return, minus a small, predictable cost. A larger-than-expected tracking error undermines that core promise, suggesting the fund is not managing its passive replication as efficiently as a comparable, well-run alternative might.
For index funds and ETFs, tracking error arises from several sources: the expense ratio (the single largest contributor), cash drag from holding a small cash balance for redemptions, transaction costs during index reconstitution, and timing differences in processing dividends from underlying stocks. A well-run Nifty 50 index fund should have an annualised tracking error below 0.3-0.5%. An ETF might have even lower tracking error on a NAV basis, but the investor's actual tracking error is worse if the ETF trades at a premium or discount to NAV.
Comparing tracking error across similar funds
When two index funds both track the same underlying index, tracking error is one of the more useful figures for choosing between them, alongside the expense ratio itself. A fund with a noticeably higher tracking error than a peer tracking the identical index is, in effect, delivering a less faithful, less efficient version of the exact same passive strategy.
How PriLytics helps. PriLytics lets you compare any fund's actual returns directly against its benchmark over any period, making tracking error immediately visible rather than something you have to dig for. Compare against a benchmark.
When comparing index funds that track the same benchmark, the fund with the lowest combination of expense ratio and tracking error is the clear winner, since the portfolios are otherwise identical. For active funds, tracking error should be evaluated alongside active return (the return above the benchmark). A high tracking error with no active return means the manager is deviating from the benchmark without benefit. High tracking error with positive active return suggests the deviations are paying off. The ratio of active return to tracking error is called the information ratio, and it is the most precise measure of active management skill.