Mutual fund tracking error measures how much the daily return gap between a fund and its benchmark varies. Tracking difference measures the return gap itself over a stated period. Both help explain index fund disclosures, but they answer different questions. A small tracking error does not establish that the fund has delivered exactly the same return as its index, and neither number promises a future return.
| Measure | Question it answers | What to check |
|---|---|---|
| Tracking error | How variable is the daily return gap? | Observation period and annualisation method |
| Tracking difference | How far apart are fund and index returns? | Period, sign convention and matching benchmark |
| Expense ratio | What recurring expenses are charged? | Exact scheme plan and disclosure date |
What is tracking error in mutual funds?
An index is a calculated reference portfolio. A fund attempting to follow it owns securities, holds cash and incurs expenses. Its net asset value, or NAV, therefore need not move by precisely the same percentage as the index each day. The issue is especially relevant when reading disclosures for an index fund or an exchange traded fund.
The definition in the scheme document hosted on AMFI describes tracking error as the annualised standard deviation of the difference in daily returns between the scheme NAV and the underlying index. Standard deviation describes dispersion: whether observations stay close together or move further away from their average.
That definition has a practical consequence. If a fund repeatedly trails its benchmark by a similar small amount, its tracking error can still be low. The daily gap is stable. A different fund can end a period close to its benchmark but have larger daily deviations along the way. The endpoint alone cannot reveal the variability measured by tracking error.
Tracking error calculation: start with daily returns
The daily return calculation is: return = (current value divided by previous value minus 1) multiplied by 100. Apply it separately to the fund NAV and the matching benchmark value. Then calculate each day's gap as fund return minus benchmark return. Tracking error uses the standard deviation of that sequence, annualised according to the stated methodology.
For a hypothetical day, a NAV rising from Rs 100 to Rs 101 has returned 1%. If the matching index rises from 1,000 to 1,011, its return is 1.1%. The day's fund minus index gap is negative 0.1 percentage point. This calculation is an illustration created for this guide, not an observation about a real scheme.
Now imagine three daily gaps of negative 0.1, negative 0.1 and negative 0.1 percentage point. Their standard deviation is zero because they are identical. Gaps of negative 0.3, positive 0.1 and negative 0.1 have the same arithmetic average, but vary around it. These simplified sequences demonstrate variability; three days are not a substitute for the observation history needed in a published annualised statistic.
What is tracking difference?
Tracking difference concerns the annualised return difference between the scheme NAV and the underlying index in the cited document. For a simple one year illustration, suppose the fund returns 9.4% and the matching benchmark returns 10%. Using fund minus benchmark, the difference is negative 0.6 percentage point. The illustration describes a gap and says nothing about how that gap behaved each day.
Always read the label explaining which return is subtracted from which. A presentation using benchmark minus fund would show the same shortfall as a positive figure. Also distinguish percentage points from a percentage change. Subtracting 9.4% from 10% produces 0.6 percentage point, not a statement that the fund's value fell by 0.6%.
Why do index fund returns differ from the index?
The official document identifies expenses, cash holdings, delays in buying or selling securities, valuation differences, corporate actions and changes in index constituents as possible causes. Securities must also be bought in whole quantities. Reproducing every benchmark weight exactly can be difficult when cash arrives, redemptions occur or trading is interrupted.
This is why the expense ratio and tracking measures should be read separately. Expenses can contribute to a gap, but they are not its only possible cause. Our guides to expense ratios and plan labels and how NAV is calculated explain the related accounting terms.
How to check tracking error on AMFI
Open the AMFI tracking error and tracking difference page. The public page presents the two measures, a Select Mutual Fund control, a Tracking Date field and a Go button. Choose the required measure, mutual fund and date, then use Go. Read the returned disclosure's own period and scheme labels before interpreting any number.
Compare like periods, like benchmarks and the exact plan named in the disclosure. A dated figure is historical evidence, not a permanent property of a fund. This guide does not rank funds or reproduce a live league table. For the wider meaning of the portfolio's risk label, read our mutual fund Riskometer explainer. Close benchmark replication still leaves the investor exposed to movements in that benchmark.
