What moves an ETF price

Two layers, not one 

Every move in a fund's listed price decomposes into two parts, and keeping them separate answers most questions about why a fund did something its holdings did not. The first layer is the portfolio: the fund holds securities, those securities have prices, and the sum of them divided by the shares in issue is the fund's net asset value. The second layer is the fund's own order book, where buyers and sellers of the fund's shares meet and can push its price a little above or below that value. The first layer accounts for almost all of the movement almost all of the time. The second accounts for the residual, and it is the part that widens exactly when conditions are difficult.

The first layer: what moves the holdings 

There is no general answer, because a fund is a wrapper and the wrapper does not have drivers of its own. What moves the portfolio is whatever moves the market the portfolio is in, and that has to be read off the fund's holdings.

• A broad equity fund moves with the earnings and valuation of hundreds of companies, aggregated by weight, so the largest constituents dominate the daily result even in a fund holding a very long list.
• A sector fund moves with the conditions specific to one industry group, which can run in the opposite direction to the broad market for extended periods.
• A bond fund moves inversely to yields, with its sensitivity set by the duration of its holdings, and a corporate bond fund adds the credit spread as a second driver.
• A commodity fund moves with the raw material, and a futures based one also moves with the shape of the futures curve as its contracts are rolled.
• A foreign market fund moves with the local market and with the currency between that market and the fund's quotation currency, and either component can dominate on a given day.

Scheduled macroeconomic events reach all of these through the same channel, which is the price of the holdings. A central bank decision, an inflation print or a labour market release moves government yields and expectations, and every portfolio holding assets priced off those yields responds. That is why funds holding quite different assets can move together on the day of a large release and diverge again afterwards.

The second layer: what moves the deviation 

The gap between a fund's price and its net asset value is held small by creation and redemption, and it widens whenever that mechanism becomes more expensive or less available. Four conditions do this reliably. The market for the holdings is closed, which is the ordinary state of affairs for a fund holding foreign shares during the American session. The holdings are illiquid, which is the ordinary state of affairs for corporate bond funds, so their published net asset value relies on model prices while the fund's own price does not. The market is moving very fast, so the risk carried between the two legs of the arbitrage rises and firms demand more of a gap before doing it. Or a fund's creation facility is constrained, which happens for funds whose underlying markets are subject to quotas or position limits.

A widening deviation is frequently misread as the fund breaking. In the two most common cases it is the opposite: the fund's exchange price is a live transaction and the net asset value is a stale or modelled estimate, so the fund is leading rather than deviating. The distinction is checkable, because both numbers and the times at which they were struck are published.

Moves that are mechanical rather than directional 

Several moves in a fund's price carry no information about the market at all. On the ex distribution date the fund's price steps down by approximately the amount being paid out, because the cash leaves the portfolio; a holder of the shares receives the distribution, so nothing has been lost, but a price chart shows a fall. Index review dates force the fund to trade its holdings to match a new constituent file. A share split in the fund itself divides the price and multiplies the share count. Corporate actions in the holdings, including mergers and spin offs, change what the fund holds without any decision by the fund.

The shape of the session 

Movement is not spread evenly through the day. The opening auction resolves everything that happened while the exchange was closed into one price, which is why a fund's largest single move of the day is often its first, and why funds holding foreign or overnight traded assets gap at the open more often than domestic equity funds. The closing auction concentrates the largest volume of the session, because index funds, benchmark linked strategies and funds resetting daily exposure all deal at or near the official close.

Bid offer spreads follow the same shape. They are widest at the open, when the value of the portfolio is least certain, narrow through the session while the underlying market trades alongside the fund, and can widen again into a holiday or ahead of a scheduled release. Volume is a separate question from liquidity: a fund with modest daily volume can still be dealt in size, because the creation mechanism means a market maker can source shares from the basket rather than from the order book.

Reading a move that looks wrong 

When a fund's move does not match the market it is supposed to represent, the explanation is usually one of a small set. The fund went ex distribution. The index it follows was reconstituted. The currency moved and the fund is unhedged. The home market of its holdings was closed, so the fund is pricing an expectation rather than a transaction. The fund holds a sampled portfolio rather than the full index. Or the deviation from net asset value changed while the portfolio did not. Every one of those is checkable against documents the issuer and the index provider publish, which is what separates them from an unexplained move.