The market value, position profit/loss, and real-time risk control of options are uniformly calculated using the Mark Price. The daily profit/loss of options is calculated using the Mark Price and the Previous Mark Price (Pre-mark).
General Rules for determining the Mark Price:
When the last price lies between the best bid and best ask, the Mark Price is equal to the last price.
When the last price is not between the best bid and best ask or does not exist, the Mark Price is set to the mid-price (for single-leg option, mid-price generally equals to the average of the best bid and the best ask).
If the ask price does not exist and the last price is lower than the best bid, the Mark Price is set to the best bid.
If the ask price does not exist and the last price is higher than the best bid, the Mark Price is set to the last price.
If the bid price does not exist and the last price is lower than the best ask, the Mark Price is set to the last price.
If the bid price does not exist and the last price is higher than the best ask, the Mark Price is set to the best ask.