Tracking error measures how closely a fund's return matches its benchmark index. It exists because a product carries fees, may sample instead of holding every member, handles currency differently, and rebalances on its own schedule.
How it works
Tracking error is measured as the deviation of the fund's return from the index, either as a cumulative gap or as the volatility of that deviation over time.
A smaller tracking error usually reflects a lower-cost or better-run vehicle.
Why it matters
Tracking error is how you compare two funds tracking the same index: the index is the same, so the difference is in the vehicles.
It is not a sign of failure; it is the normal toll of running a product that follows a rule.
A simple market example
Two ETFs track the same index. One trails it by 0.1% annually because of low fees and full replication; the other trails by 0.6% because of higher fees and heavy sampling. The difference is tracking error.
Common mistakes
Judging a fund by whether it matches the index exactly, which no product does in practice.
Assuming a bigger tracking error always means a bad fund, without checking why it exists.
Frequently asked questions
Can an ETF ever match its index exactly?
Not in practice. Fees, sampling, currency, and rebalancing always create some difference.
Is a bigger tracking error always worse?
Usually, but it depends on the cause: high fees are a real cost, while some sampling is a design choice.
How do I compare two funds?
Check both the index rule and the vehicle terms: fees, tracking method, currency, and reported tracking error.
Educational content only. Definitions describe common market usage and may vary by jurisdiction, instrument, or institution.