ETF Expense Ratio, Tracking Error and NAV: How to Evaluate an ETF

Two ETFs can track the same index and still leave investors with noticeably different outcomes over time. The difference usually comes down to three factors: expense ratio, tracking error, and the gap between an ETF's NAV and market price. The expense ratio affects how much of the fund's return you keep, tracking error shows how consistently it follows the benchmark, and the NAV-to-market-price gap influences the price you actually pay when buying or selling.

Looking at any one of these numbers in isolation can be misleading. A low-cost ETF may still track poorly, while a tightly tracked fund can be expensive to trade if liquidity is weak. 

In this blog, we'll look at what each metric means, what a good number looks like, and how to use all three together to compare ETFs more effectively before investing.

What is an expense ratio, and what it costs you

The expense ratio is the annual fee an ETF charges to cover its running costs, such as fund management, custody, and record-keeping. You never get a separate bill for it. The fee is deducted from the fund's NAV each day before it is published, so it quietly reduces the return on every unit you hold.

For plain index-tracking ETFs, this cost is usually small. Large, liquid Nifty 50 ETFs in India commonly charge in the 0.01%-0.07% range, while gold ETFs run higher, roughly 0.33%-0.70%, because storing and insuring physical gold adds cost. SEBI caps how much an index fund or ETF can charge, so the ceiling stays low across the category.

A small gap in the ETF expense ratio matters more than it looks, because it is subtracted every year rather than once. On a ₹1,00,000 investment growing at 10% a year for 20 years, a fund charging 0.05% would leave you with about ₹6,66,660, while one charging 1.00% would leave you with about ₹5,60,441, a difference of roughly ₹1,06,219. Over a long holding period, that small gap compounds firmly in the cheaper fund's favour.

Tracking error: how closely an ETF follows its index

An ETF is meant to mirror its index, but it never does so perfectly. Tracking error tells you how consistently the fund keeps pace with its benchmark. SEBI defines it as the annualised standard deviation of the daily return difference between the ETF's NAV and its index, measured over a rolling one-year period. In plainer terms, a low tracking error means the ETF closely tracks its index day after day.

For equity ETFs and index funds, SEBI caps annualised tracking error at 2%. In practice, large Nifty 50 ETFs remain well within that limit, often around 0.02%- 0.05%. A high or rising tracking error in an ETF is a warning sign that the fund is struggling to replicate its benchmark.

A few things push an ETF away from its index. It holds a little cash that earns less than the index return, and it pays trading costs whenever the index reshuffles its holdings. The expense ratio adds to this drag every day, which is why the gap usually runs against you.

It also helps to read tracking error alongside tracking difference, which measures the difference between the ETF's return and its benchmark over a specified period.  A fund can track smoothly yet still trail its index if a steady cost drag eats into returns, so checking both gives you the fuller picture.

NAV, market price and the premium or discount

An ETF has two prices, and confusing them can cost you. The NAV represents the per-unit value of the ETF's underlying assets after accounting for its liabilities and is calculated at the end of the valuation period.  It works out to the value of the fund's holdings plus cash, minus liabilities, divided by the number of units outstanding. The market price is simply the last price at which the ETF traded on the NSE or BSE, determined by live buy and sell orders.

Because these two can drift apart during the day, exchanges publish an indicative NAV (iNAV) during market hours, allowing investors to compare the ETF's market price with an estimate of its underlying value. You can check the live market price against the iNAV to see whether the ETF is trading at a premium (above its value) or a discount (below it).

Large institutions called Authorised Participants keep this gap small. When an ETF drifts too far from its iNAV, they step in to create or redeem units to arbitrage the difference. Liquid ETFs generally tend to trade closer to their underlying value, while less-liquid ETFs can experience wider premiums or discounts. The lesson for you is simple: a liquid ETF is cheaper and safer to enter and exit.

How to evaluate an ETF using all three

No single number tells you whether an ETF is worth buying. A cheap fund can track poorly, and a tightly tracked fund can be expensive to trade. Work through the three in order.

1. Start with tracking error. If a fund's tracking error is high or near the 2% ceiling without a clear reason, it fails at its main job, so rule it out first.
2. Compare the expense ratio next, among the funds that track well. Since this cost compounds daily, prefer the lower one, and take the exact figure from the fund's own factsheet.
3. Check liquidity last, but don't skip it. A wide bid-ask spread or high impact cost is paid on every trade and can outweigh a few basis points saved on fees.

On that last point, NSE treats an impact cost of 0.50% or lower as a mark of a liquid, easily traded security. Thin trading volume is a reason to be cautious, however low the expense ratio looks.

#Conclusion

Evaluating an ETF means looking at cost, tracking quality, and trading efficiency together. The expense ratio affects long-term returns, tracking error shows how closely the fund follows its index, and the gap between NAV and market price influences what you actually pay to buy or sell. Comparing ETFs on all three gives a much clearer picture than choosing on fees alone.

Open a demat account with SMC to invest in ETFs and hold them alongside your other market investments.

Investments in securities markets are subject to market risks. Read all the related documents carefully before investing.