The market price of an ETF share is determined by the net asset value (NAV) of the underlying portfolio as well as supply and demand in the marketplace. Bid-ask spreads and premiums and discounts to NAV may also impact the price an investor pays for an ETF share. For more details on how ETFs work, click here. Bid/ask spread is the amount by which the ask price exceeds the bid price for an asset in the market.