Stock index futures use margin trading. In order to control risks, according to regulations, futures companies should settle profits and losses for customers every day, and book profits can be withdrawn, but book losses should be made up by margin. If the customer has a position, the basis for calculating the profit and loss of the position is the daily settlement price, then the cost price of the remaining position becomes the settlement price of the day after clearing the profit and loss.

Risk warning: Many stock investors often don't understand this problem when they do futures trading for the first time. After buying a stock, as long as you don't sell it, the profit and loss are on the books and can be ignored. However, futures are different. They are all margin transactions, and the profit and loss are settled every day. Book profits can be withdrawn, but book losses must be covered by margin. The basis of calculating profit and loss is the daily settlement price, so the cost price of the remaining positions becomes the settlement price of the day after profit and loss settlement.