TER vs Tracking Difference: What an ETF Really Costs You

Written by Thomas Lovas Lokoy — researched and drafted with AI assistance from published sources; edited and published by NorwegianSpark SA · Last updated: August 2026

Capital at risk. Fund values fall as well as rise. Costs reduce returns but low costs do not make an investment safe, and past tracking behaviour does not predict future tracking behaviour. Nothing here is advice.

Investors have been trained, correctly, to care about fees. They have then been handed one number — the ongoing charge, the TER — and left to believe it is the cost. It is not. It is one component, it is the one component the provider chooses to advertise, and a fund with the lower TER can quite easily be the more expensive fund to own.

There is a number that captures everything, it is published, and almost nobody looks at it.

The costs that exist, in order of how well they are hidden

The ongoing charge (TER or OCF). The management fee plus the fund's running costs, accrued daily and taken out of the fund's value. You never see it leave; it shows up as slightly lower performance. This is the advertised number.

Transaction costs inside the fund. When the index changes, the fund trades, and trading costs money — commissions, taxes, and the market impact of buying what everyone else tracking that index is also buying. These are real, they are borne by you, and they are not in the TER.

Securities lending. Many funds lend out their holdings and keep some of the fee. This runs the other way: it can offset costs, occasionally to the point of a fund beating its index before tax. It also introduces counterparty risk, which is disclosed and is usually collateralised, but is not zero.

Withholding tax on the fund's income. The fund's domicile determines what it recovers on foreign dividends, and that difference is frequently larger than the entire management fee. See foreign dividend withholding tax.

Cash drag. Income sitting uninvested between receipt and reinvestment is not tracking the index.

The bid-ask spread. Your own cost of getting in and out, paid on every trade.

Platform and custody fees, and FX conversion. Charged by your broker, not the fund, and easily the biggest line for a small portfolio.

Tracking difference: the number that contains the answer

The first five of those are all internal to the fund, and there is a single measurement that captures every one of them at once.

Tracking difference is the fund's actual return minus the index's return over the same period. It is the total of everything the fund did to your money, net of everything it recovered.

A fund with a stated 0.20% ongoing charge that returned 0.35% less than its index cost you 0.35%, whatever the factsheet says. A fund with a 0.25% charge that lagged by 0.18% — because securities lending and a favourable domicile paid for part of the fee — cost you 0.18%, and it is the cheaper fund despite the higher headline.

This is not obscure data. Providers publish fund returns; index providers publish index returns. Compare like with like over the same calendar periods, several years of them, and you have the real cost. Look at several years rather than one — a single year can be distorted by an index change or a one-off.

Two cautions that decide whether the comparison is valid at all.

Compare against the same index variant. A total-return index that assumes dividends reinvested gross of withholding tax is not the same benchmark as one that assumes net. A fund measured against the wrong variant will look worse — or better — than it is.

Do not confuse tracking difference with tracking error. Tracking difference is how far behind (or ahead) the fund ended up. Tracking error is how consistently it tracked — the volatility of the gap. A fund can have a tiny tracking error and still lag persistently, which is a very well-behaved way of costing you money every single year.

An illustration of why the headline fee misleads

Purely arithmetic, to show the shape. These are not real funds and not a forecast.

Fund A wins every fee comparison table and loses on the only measurement that matters. Nothing here is unusual: an ultra-low headline fee has to be paid for somewhere, and the places it gets paid for — internal trading, domicile, lending policy — are exactly the places the headline does not look.

The spread, and when it is worth caring about

The bid-ask spread is the gap between what you pay to buy and what you receive to sell. On a large, heavily traded fund it is small enough to ignore for a long-term holder. It stops being ignorable in three situations.

The practical rules are unglamorous: trade during the underlying market's own hours where you can, use limit orders rather than market orders, and do not rebalance more often than your strategy actually requires. Common investing mistakes covers the behavioural half of that.

The costs your broker adds

None of the above includes what your platform charges: a percentage custody fee, a flat account fee, per-trade commission, and the FX spread applied when you buy a fund priced in another currency.

For a small portfolio these usually dominate everything internal to the fund. A fixed annual fee is a large percentage of a small balance, and a percentage fee is a large absolute number on a big one — which of those is cheaper flips at a crossover point you can calculate in about a minute with your own numbers. How to pick a stock broker works through the comparison.

The FX line deserves specific attention because it is the one most often overlooked. Buying a dollar-priced fund from a euro account means a conversion, and the rate applied is not the interbank rate. On a regular monthly purchase that conversion can quietly cost more than the fund does.

The proportion problem

One closing thought on where the effort belongs. Costs are the part of investing you control completely, which makes them worth minimising. They are also, for most portfolios, smaller than the difference made by the asset allocation and by whether you keep contributing through a bad decade.

Spending an afternoon on tracking difference is worthwhile. Spending three months choosing between two broad index funds that differ by four basis points, while not investing, is not.

This article is for informational purposes only and does not constitute financial advice. Always consult a qualified financial adviser before making investment decisions.

About this article

This article was written by Thomas Lovas Lokoy — researched and drafted with AI assistance from published sources; edited and published by NorwegianSpark SA. YieldNav is operated by NorwegianSpark SA (org. 834 984 172), founded by Thomas Lovas Lokoy. We are not licensed financial advisers, and nothing here is personalised advice. Read our about page, editorial policy and affiliate disclosure.