The accurate timing of your fertile and safe period, depends on the regularity of your mesntrual cycle. and only in the context of a regular menstrual cycle, can your fertile and safe period be accurately timed. In a regular menstrual cycle, menstruation usually occurs 14 days after ovulation, such that if your cycle length is 30 to 32 days, then you probably ovulate on the 16th to 18th day of your menstrual cycle. But if your menstrual cycle is irregular, because ovulation is absent in most irregular cycles and even when it occurs, it is usually unpredictable, your ovulation day and therefore, your fertile and safe period cannot be calculated. To calculate your cycle length and your likely ovulation date kindly read NORMAL AND ABNORMAL MENSTRUAL PERIOD. Because the male sperms can live up to 5 days in the female reproductive organs and the ovum or egg can live up to 24 hours after ovulation, and because of the subtle variation in the follicular phase of a normal menstrual cycle, the fertile period is usually a 10 day period starting from about 7 days or a week before your likely ovulation date to about 3 days after your likely ovulation date. The the safe period on the other hand is any other day apart from your fertile period. For further information, please read the article UNDERSTANDING YOUR FERTILE AND SAFE PERIOD or CHAT WITH OUR CONSULTANTS.