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.
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.
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.