An ETF performs two jobs at once: it holds a pooled portfolio like a fund and trades throughout the day like a listed security.
That combination creates a structure with two markets layered together.
- Retail investors generally buy and sell ETF shares with other market participants on an exchange.
- Large financial institutions known as authorised participants can create or redeem large blocks of ETF shares directly with the fund under its operating structure.
The first market gives investors intraday trading. The second market helps keep the ETF’s exchange price connected to the value of the portfolio underneath.
This article is part of Batch 035 of the eduKateSG Finance Authority 400. Mutual Funds owns the pooled open-end fund structure. This page owns the ETF market architecture: exchange trading, authorised participants, creation/redemption, premiums, discounts and arbitrage. The companion NAV article owns fund accounting value, while Index Funds owns rule-based portfolio construction.
An ETF is not merely a mutual fund with a ticker. Its share-trading and creation-redemption machinery changes how investors enter, exit and price the vehicle.
Educational boundary: this article focuses on ETFs structured as regulated pooled investment funds. Other exchange-traded products, including some notes or commodity structures, can have different legal and economic mechanics.
The short answer: what is an ETF?
An exchange-traded fund is a pooled investment vehicle whose shares trade on a securities exchange at market prices while a primary-market creation and redemption process connects large blocks of ETF shares to the fund’s underlying portfolio.
The SEC’s 2023 ETF bulletin explains that retail investors generally do not purchase or redeem individual ETF shares directly from the ETF. Instead, retail investors trade ETF shares on an exchange. Authorised participants typically create and redeem large blocks called creation units directly with the fund. See Updated Investor Bulletin: Exchange-Traded Funds.
The two-market map
PRIMARY MARKET: AUTHORISED PARTICIPANT ↔ ETF FUND.
SECONDARY MARKET: INVESTOR ↔ EXCHANGE ↔ OTHER INVESTORS / MARKET MAKERS.
The secondary market is where ordinary investors see prices moving throughout the trading day.
The primary market sits behind the screen. It changes the supply of ETF shares when authorised participants create or redeem large blocks.
The two layers interact through arbitrage and inventory management.
Retail investors trade ETF shares, not the portfolio directly
When a retail investor buys 100 ETF shares on an exchange, the seller is usually another market participant.
The investor does not instruct the ETF sponsor to sell 100 proportional pieces of every underlying security.
Ownership of ETF shares changes in the secondary market.
This separates ETFs from conventional mutual funds, where retail subscriptions and redemptions generally occur with the fund at the next calculated NAV.
Authorised participants connect the ETF to the underlying assets
An authorised participant, or AP, is typically a large broker-dealer or financial institution that has an agreement with the ETF sponsor allowing it to create and redeem ETF shares in large blocks.
The SEC’s ETF bulletin explains that these large blocks are commonly called creation units and can involve exchanges of baskets of securities and other assets with the ETF.
The AP is not necessarily the same institution as the investor’s broker, market maker, custodian or ETF manager, although one firm can perform several roles under different capacities.
Creation: increasing ETF share supply
Consider a simplified equity ETF whose portfolio mirrors a basket of securities.
If market demand pushes the ETF price materially above the value of the underlying basket, an authorised participant can have an incentive to acquire the required basket, deliver it to the ETF and receive newly created ETF shares.
The AP can then sell those ETF shares in the market.
UNDERLYING BASKET → ETF → NEW CREATION UNIT → MARKET SUPPLY OF ETF SHARES INCREASES.
Additional supply can help reduce the premium.
Redemption: reducing ETF share supply
If ETF shares trade below the value of the underlying basket, an AP may have an incentive to buy ETF shares, assemble enough for a creation unit and redeem them with the fund in exchange for the underlying basket or permitted redemption assets.
ETF SHARES → ETF → REDEMPTION BASKET → MARKET SUPPLY OF ETF SHARES DECREASES.
The AP can sell or otherwise use the underlying assets received.
Removing ETF share supply can help reduce the discount.
Why creation and redemption help keep price near NAV
The creation-redemption mechanism creates an arbitrage link between two prices:
- the market price of ETF shares;
- the value of the underlying portfolio basket.
If the gap becomes large enough to exceed trading, financing, operational and risk costs, market participants can have an economic incentive to trade against the difference.
This does not guarantee that price always equals NAV exactly.
It creates a mechanism that tends to resist persistent large differences when the underlying markets and creation-redemption process function normally.
Premium and discount
An ETF trades at a premium when its market price is above the relevant NAV per share.
It trades at a discount when market price is below NAV.
Investor.gov’s ETF materials explicitly distinguish ETF market price from NAV and explain premiums and discounts.
Suppose an ETF’s NAV is S$20.00 per share.
| Market price | Relationship to NAV | Difference |
|---|---|---|
| S$20.10 | Premium | +0.50% |
| S$20.00 | At NAV | 0% |
| S$19.80 | Discount | −1.00% |
The difference can change throughout the day even while the official NAV is calculated only at defined intervals.
Intraday value is an estimate, not the same as official NAV
ETF investors trade before the fund’s official end-of-day NAV is known.
Market makers therefore use current prices of underlying holdings, futures, currency markets and other data to estimate the portfolio’s intraday value.
If underlying markets are closed or securities are difficult to price, that estimate becomes less certain.
An apparent premium or discount can therefore reflect stale underlying prices rather than a pure arbitrage opportunity.
International ETFs make stale-price risk visible
Imagine an ETF trades in Singapore or the United States while some underlying foreign stock exchanges are closed.
News arrives that materially changes the expected value of those foreign shares.
The ETF can reprice immediately because it is trading now. The official last prices of the underlying securities cannot update until their markets reopen.
The ETF may appear to trade at a large premium or discount relative to stale NAV inputs even though the ETF market is doing the faster price discovery.
This is a good example of why valuation timestamps matter.
ETF liquidity has two layers
ETF liquidity is not determined solely by the number of ETF shares changing hands.
There is:
- secondary-market liquidity in the ETF shares;
- underlying-market liquidity in the securities or assets held by the ETF.
An ETF with low visible trading volume can still accommodate a large trade if market makers and APs can efficiently access a deep underlying portfolio.
An ETF with seemingly active trading can become difficult when the underlying assets themselves become illiquid.
The wrapper does not manufacture liquidity independent of the assets forever.
Bid-ask spread is an investor cost
Because ETF shares trade on exchanges, investors face bid and ask prices.
Suppose the best bid is S$9.98 and the best ask is S$10.02.
The visible spread is S$0.04, or about 0.4% of the mid-price.
An investor who buys at the ask and immediately sells at the bid loses the spread before any change in underlying value.
Expense ratio measures fund-level recurring costs. Bid-ask spread is a trading cost. Both can matter.
Market orders can create execution risk
An ETF is an exchange-traded security, so order mechanics matter.
A market order prioritises execution over price.
During volatile or thin conditions, a large market order can sweep through several price levels.
A limit order constrains the acceptable price but may not execute.
The existing Exchanges article owns the general order-book mechanism. ETFs inherit that market structure.
An ETF can be active or index-based
ETF describes the vehicle and trading structure.
It does not determine the investment strategy.
- An ETF can track a broad market index.
- An ETF can track a narrow or custom index.
- An ETF can be actively managed.
- An ETF can hold bonds, equities or other permitted assets.
This is why “ETF” should not be treated as a synonym for “passive.”
The companion Index Funds article owns the portfolio-rule distinction.
Portfolio transparency supports arbitrage
Many ETFs disclose portfolio holdings frequently enough for market makers and APs to estimate the value of the basket and hedge exposures.
The SEC’s ETF bulletin notes that most ETFs publish portfolio holdings daily.
Transparency is economically useful because arbitrage becomes harder when market participants do not know what they are arbitraging against.
Some active ETF structures use different disclosure or basket mechanisms under applicable rules. The exact architecture matters.
In-kind creation and redemption can reduce forced cash trading
Many ETFs create or redeem using baskets of securities rather than only cash.
This can allow the ETF to receive or deliver underlying securities without selling the whole proportional portfolio for every shareholder flow.
That can reduce transaction friction and, in some jurisdictions, create tax-efficiency advantages relative to certain mutual-fund structures.
Tax outcomes depend on local law and should not be universalised.
The creation basket need not always be an exact copy of the portfolio
Operationally, an ETF can use a specified basket representing the assets required for creation or redemption.
Depending on the fund and applicable rules, the basket can include cash or differ from the full portfolio.
This means the arbitrage mechanism relies on the economic relationship between the basket and the ETF, not on a simplistic assumption that every creation moves one exact microscopic slice of every holding.
Authorised participants are not obligated to eliminate every premium immediately
Arbitrage works when the expected profit exceeds the costs and risks.
During market stress:
- underlying spreads widen;
- financing becomes expensive;
- hedges become imperfect;
- basket execution becomes uncertain;
- operational limits tighten.
A premium or discount can therefore widen because the cost of closing it has risen.
The AP mechanism is an incentive structure, not a guaranteed price peg.
Bond ETFs reveal price-discovery differences during stress
Individual bonds can trade infrequently. An ETF holding many bonds can trade continuously.
During stress, ETF prices can move faster than evaluated prices on underlying bonds.
A discount to reported NAV can therefore represent several possibilities:
- true selling pressure in the ETF;
- stale underlying bond marks;
- the cost of liquidating the basket;
- credit or liquidity risk repricing;
- a mixture of all four.
The gap must be diagnosed rather than automatically labelled a market failure.
Tracking error is portfolio implementation risk
An index ETF seeks to track an index, but its return can differ.
Sources include:
- fund expenses;
- transaction costs;
- cash balances;
- tax and withholding;
- sampling instead of full replication;
- corporate actions;
- timing of index rebalances;
- securities lending revenue;
- market impact.
The companion Index Funds article owns the broader tracking-rule mechanism.
Tracking difference and tracking error are not the same
Tracking difference usually refers to the average return difference between the fund and its benchmark over a period.
Tracking error commonly refers to the variability of that return difference.
A fund can consistently lag its benchmark by 0.20% with very low tracking error.
Another can average almost zero difference but fluctuate around the index substantially, producing high tracking error.
The first has a stable drag. The second has unstable replication.
ETF distributions move value out of the vehicle
Like mutual funds, ETFs can receive dividends, interest and realised capital gains from their portfolios and can make distributions to shareholders.
The SEC’s 2026 fund-distributions bulletin explains that a distribution reduces fund NAV because value has left the vehicle.
The ETF market price normally adjusts as well, although market trading can create a different exact path.
A cash distribution is therefore not an extra return layered on top of unchanged fund value.
ETF fees are only part of the investor cost
A low expense ratio does not guarantee low total ownership cost.
Investors can also face:
- bid-ask spread;
- brokerage commission where applicable;
- premium paid above NAV;
- market impact;
- tax;
- FX conversion;
- advice or platform fees.
The SEC’s 2025 Fees and Expenses bulletin emphasises that expenses reduce fund returns and that investor-level costs should also be understood.
The ETF can close even if the index survives
An ETF sponsor can decide to liquidate or merge a fund subject to the relevant process.
The S&P 500, a bond index or a thematic benchmark can continue existing while one particular ETF tracking it closes.
Vehicle risk and benchmark risk are therefore separate.
An investor may need to reinvest proceeds, incur tax or transaction costs, or lose access to a preferred structure even if the underlying investment idea remains unchanged.
Leveraged and inverse ETFs are different machines
Some ETFs seek a multiple or inverse multiple of an index’s daily performance.
Daily reset and compounding mean the result over longer periods can diverge substantially from simply multiplying the index’s long-period return by the stated factor.
These products contain derivatives, financing and path-dependence that deserve a separate specialist treatment.
The ordinary ETF mechanism should not be stretched to cover them as though every ETF were the same product.
A worked creation-arbitrage example
Consider a simplified ETF with NAV S$100 per share.
Market demand pushes the ETF price to S$101. Assume a creation unit contains 50,000 shares and ignore all costs.
An AP can acquire the underlying basket worth S$5 million, deliver it to the ETF and receive 50,000 ETF shares. Selling those shares at S$101 raises S$5.05 million.
The gross theoretical arbitrage is S$50,000 before financing, bid-ask spreads, market impact, taxes, operational costs and price risk.
In reality, those costs determine whether the trade is attractive and how close ETF price remains to NAV.
A worked discount example
Now suppose the same ETF trades at S$98 while the underlying redemption basket is worth S$100 per share.
An AP could buy 50,000 ETF shares for S$4.9 million and redeem them for a basket worth S$5 million, creating a theoretical S$100,000 gross difference before costs and risk.
The potential arbitrage creates buying pressure on the ETF and selling pressure on the underlying basket, tending to close the gap.
Again, this is an incentive mechanism, not a guaranteed outcome.
ETF versus mutual fund
| Feature | Conventional mutual fund | ETF |
|---|---|---|
| Retail transaction | With fund | On exchange |
| Retail price | Next calculated NAV | Intraday market price |
| Direct creation/redemption | Retail investor can generally subscribe/redeem | Typically authorised participants in large blocks |
| Bid-ask spread | Not an exchange-trading feature | Yes |
| Premium/discount to NAV | Generally not the retail transaction mechanism | Possible intraday |
| Portfolio strategy | Active or index | Active or index |
The vehicle structure changes trading and liquidity. It does not determine which portfolio is held.
Failure-first reading: what can break the ETF mechanism?
- Underlying markets become illiquid.
- Authorised participants step back because arbitrage becomes too risky.
- Market makers widen spreads dramatically.
- Portfolio values become stale or difficult to estimate.
- Creation baskets become expensive to source.
- Exchange trading is halted while underlying markets continue moving—or vice versa.
- The ETF’s strategy contains leverage or options that investors did not understand.
- The fund is too small to remain commercially viable.
The ETF wrapper can improve access and liquidity transmission. It cannot repeal the economics of the assets underneath it.
The ETF diagnostic
- What legal fund structure is this?
- What portfolio does it own?
- Is the strategy active or index-based?
- How does the retail investor trade?
- Who are the authorised participants?
- What is the creation/redemption basket?
- How liquid are the underlying assets?
- How wide is the ETF bid-ask spread?
- How large are premiums and discounts to NAV?
- How current are underlying prices?
- What recurring expenses apply?
- What investor-level trading costs apply?
- How closely does the fund track its objective?
- What happens if APs or market makers withdraw?
- What happens if the fund closes?
Observable mastery test
An ETF’s official NAV is S$50. Its market price is S$48 during a period when several underlying bond prices have not traded for hours. A reader says, “The ETF is definitely 4% undervalued and arbitrage guarantees free profit.”
The correction is that the published NAV can contain stale inputs. The ETF price may be incorporating newer information about what the bonds could actually sell for. Even if a true discount exists, arbitrage requires executable baskets, liquidity, financing and willingness by APs to take the risk.
You understand the ETF when you can distinguish market price, NAV, estimated intraday portfolio value and the cost of converting one into the other.
The World Return: from exchange share back to real financing
Investor order → ETF market price → creation/redemption and portfolio holdings → underlying securities → companies / governments / markets → income, gains and losses → ETF NAV and market price → investor wealth and future spending.
The ETF does not create the underlying economic return by being easy to trade.
Its contribution is infrastructural: it packages a portfolio into a share that can trade continuously and uses a primary-market mechanism to connect that share back to the assets underneath.
The mechanism is successful when the convenience of the wrapper does not cause investors to forget the risk, liquidity and valuation of the underlying portfolio.
Research anchors
The SEC’s Updated Investor Bulletin: Exchange-Traded Funds explains secondary-market trading, authorised participants, creation units and ETF premiums and discounts. The 2025 Characteristics of Mutual Funds and ETFs bulletin provides the structural comparison with mutual funds, and the 2025 Fees and Expenses bulletin supports the cost boundary. Worked arbitrage cases are original teaching illustrations.
Continue through Batch 035
Read Mutual Funds for the pooled structure. Continue to Net Asset Value and Index Funds. Return to How Finance Works for the complete Finance map.