Menstrual cycle is calculated from the first day of your period to the first day of the next period . Safe period is from day 1 to 7 and day 21 to the rest of the cycle, when you can have sex without worrying about getting pregnant
. This period will not be the same for all women as it depends on the length of the menstrual cycle. The average menstrual cycle is 28 days or a little less, but if your cycle is longer than 28 days, the safe period is not reliable.