Menstruation has been very normal, but this month I do not know what reason has been postponed 5 day

Normal menstrual cycle is between 21-35 days, menstrual delay or seven days in advance, are normal, do not be too nervous. If menstrual delay more than seven days, first consider whether there is a possibility of pregnancy. After excluding pregnancy, may be caused by gynecological diseases, should be timely medical treatment.