gynecology and obstetrics
Fertility Awareness‒Based Methods of Contraception
Standard days method
The standard days (calendar) method is based on the calendar (the dates that menses occur) and is appropriate only for women who have regular menses. Ovulation occurs about 14 days before onset of menses. Thus, the interval of abstinence during the menstrual cycle is determined by subtracting 19 days from the shortest of the previous 12 cycles and 11 days from the longest. For example, if cycles vary between 27 and 29 days, abstinence is required from days 8 through 18 of each cycle. The greater the variance in cycle length, the longer abstinence is required. Cyclebeads (a string of color-coded beads that represent the days of a menstrual cycle) or other tools (eg, digital menstrual cycle trackers), may be used to help women keep track of their fertile days. 