The quick answer: TER is the published annual fund charge known before investing. Tracking difference is the historical gap between the ETF’s return and the correct benchmark return after fees and implementation effects. Use TER as a forward-looking baseline and matched, multi-period tracking difference as evidence of how the fund actually tracked.
The cheapest TER can still produce the wider return gap. Withholding tax, trading, sampling, cash, securities lending and swap economics can move realised tracking above or below the headline charge. Investor-level commission, spread, platform fees and currency conversion sit outside both measures.
The two measures
| Measure | Basic calculation | Best use | Main limitation |
|---|---|---|---|
| TER or ongoing charge | Published annual percentage of fund assets | Known recurring fund charge | Does not include every source of return slippage or benefit |
| Tracking difference | Fund return minus benchmark return | Historical implementation result | Backward-looking and sensitive to benchmark, period and share class |
| Tracking error | Variability of tracking differences | Consistency of benchmark tracking | Low variability can coexist with a persistent return shortfall |
Which number should you use?
Start with TER because it is current, published and known in advance. Then compare tracking difference only between funds following the same index version, over the same dates and in the same return currency. Prefer several annual periods to one isolated year. Finally add execution and account costs that never appear in the fund-versus-index calculation.
A worked example
Suppose an ETF reports a 0.12% TER. Over the same one-year period, its stated net-return benchmark gains 10.00% and the fund’s net asset value gains 9.85%.
Tracking difference = 9.85% − 10.00% = −0.15 percentage points.
The fund lagged by 0.15 points, three basis points more than the headline charge. That extra gap could reflect trading, withholding tax, cash or other implementation effects. In another year, securities-lending income or favourable tax treatment could partly offset the charge. The example does not imply that either outcome will repeat.
Benchmark convention can reverse the story
Equity indexes may be published as price, gross-return and net-return versions. A price index excludes dividends. A gross-return index reinvests dividends before withholding tax. A net-return index applies an assumed tax treatment. Comparing a fund with the wrong version can create a large apparent tracking difference that says little about fund quality.
Use the benchmark named in the prospectus or factsheet and match the fund’s base-currency, NAV-to-NAV return for the same dates. Market-price returns add exchange premiums, discounts and trading-time effects, which are important to an investor but different from portfolio tracking.
Why a fund can beat its benchmark
This guide uses fund return minus benchmark return. Under that convention, a negative number means the fund lagged and a positive number means it outperformed. Some databases reverse the formula, so always read the sign definition before comparing values.
A small positive result does not mean the manager found a free return. Possible contributors include securities-lending revenue, tax differences between the fund and benchmark assumption, sampling choices, timing and fair-value adjustments. Those effects can change. Check several periods and the fund’s disclosures before interpreting an isolated year.
Where to find the numbers
The current TER or ongoing charge appears in the KID, factsheet and issuer product page. Tracking evidence may appear in annual reports or can be calculated from official fund and benchmark returns. Record the index name, price/gross/net-return convention, date range, currency and whether the fund figure is NAV or market-price return.
A practical comparison sequence
- Confirm that the funds track the same index version.
- Compare the current TER or ongoing charge.
- Calculate annual tracking differences from matched official fund and benchmark returns.
- Look at consistency across multiple periods, not only the latest year.
- Add investor-level costs: platform charge, spread, commission, currency conversion and tax.
For a buy-and-hold comparison, headline charges set a useful baseline and tracking difference tests the historical implementation. Neither replaces the other. A fee ranking should therefore be labelled as a charge ranking, not a total-cost or performance ranking. The investment fee calculator can show how a stated annual percentage changes a long-term illustration.
Frequently asked questions
Can tracking difference be better than TER?
Yes. Securities-lending income, benchmark tax assumptions or swap economics can offset part of the published charge. That historical result can change and should not be projected as guaranteed.
Is tracking error the same as tracking difference?
No. Tracking difference measures the level of the return gap; tracking error measures how much that gap varies. A fund can lag consistently with low tracking error.
Should two ETFs with different indexes be compared by tracking difference?
Not as a fund-quality contest. Each fund must first be compared with its own stated benchmark. Different indexes represent different exposures and can produce different returns.
Sources and limitations
iShares’ global ETF comparison guide identifies TER, tracking difference, platform fees and trading costs as separate comparison inputs. BlackRock’s index glossary distinguishes tracking difference from tracking volatility.
The worked figures are an original hypothetical example. This guide does not rank a particular fund, account for personal tax or predict future tracking. Fund reports can use different return bases; verify definitions before comparing numbers.