How is the closing price determined for equities?

The closing price is determined through a closing auction, similar to how the opening price is determined in an opening auction. 

The closing auction is a session after continuous trading when investors may place orders (bid/ask). The trading engine will determine an equilibrium price at which all possible matching orders are executed at the end of the auction (uncross). The execution price is the closing price and becomes a reference price of the next day. 

The closing price is calculated based on normal trades only (SAR15,000 and above). If there are no trades during an auction, then the closing price is the last traded price (LTP) during continuous trading. If there are no trades during the day, the closing price is the closing price of the previous day.