Simple definition
Tracking error measures how far an index fund's returns drift from the index it's built to copy. A fund tracking a broad market index should move almost in lockstep with it; the small gap that remains is the tracking error. Think of it as a cover band's slight off-notes — the closer to the original, the better the fund did its one job.
Why it matters
An index fund's whole purpose is to match its benchmark, so a small tracking error usually signals it's doing its job well. Larger drift can come from fees, trading costs, or how the fund is run. Checking it helps you spot a fund that isn't delivering the index you thought you bought.
Real-life example
Suppose an index rose about 10% in a year while the fund tracking it rose 9.7%. That 0.3 percentage-point gap is the tracking error, often traceable to fees and trading costs. These are rounded, hypothetical figures to show how the gap appears, not the results of any specific fund.
Common mistakes
- Assuming an index fund will match its benchmark exactly, when some small gap is normal.
- Ignoring tracking error and focusing only on the headline expense ratio.
- Confusing tracking error with tracking difference, which measures the gap over a single period.
- Reading a low tracking error as proof the fund is a good investment overall.
Pro tips
- Favor index funds with consistently low tracking error for the index you want.
- Remember fees and trading costs are common causes of larger drift.
- Compare tracking error alongside the expense ratio, since both eat into returns.
- Check the fund's history to see whether the drift stays small year after year.
Related Money Dictionary terms
- Index FundA fund that owns a broad slice of the market at low cost — the backbone of most investing.
- Expense RatioThe yearly fee a fund charges, shown as a percentage of your investment, that covers its operating costs.
- ETF (Exchange-Traded Fund)A basket of investments that trades like a single stock, letting you own many holdings at once with one purchase.
- BenchmarkA standard index used to compare how well your investments or a fund are performing.
Frequently asked questions
Is a low tracking error always better?
For an index fund, generally yes. The fund's job is to mirror its benchmark, so a small tracking error means it's doing that faithfully. Very large drift suggests fees, trading costs, or management choices are pulling it off course. For funds meant to beat an index rather than match one, though, some deviation is expected.
What causes tracking error?
Several things pull a fund away from its index. The expense ratio quietly drags returns below the benchmark, and trading costs add up when the fund buys and sells. How the fund samples the index, holds cash, or handles dividends can also create small gaps. Together these explain why even good index funds don't match perfectly.
How is tracking error different from an expense ratio?
The expense ratio is the yearly fee the fund charges, stated up front. Tracking error is the actual gap between the fund's returns and its index, which fees are only one cause of. A fund can have a low fee yet still drift for other reasons, so the two numbers tell you related but different things.
Knowing what Tracking Error means is knowledge — the first half. A brick gets placed when you act on it: compare the tracking error of an index fund you own against the index it's meant to follow.
Sources & references
More in Investing
Plain-English education — not personalized legal, tax, or investment advice.