As per the new margin system Option sell credit can be used only to buy options on the same trading day - When you exit your long/buy option positions or enter new write/short options, the proceeds or credit of option premium can be used for only new long/buy option trades on the same trading day and only within the same segment (proceeds from equity options can’t be used for currency or vice versa). You can use these proceeds or option credit for all other types of trades only from the next trading day.