Before waiver of contraceptives and a shift to the calendar method of protection should know that a healthy woman can get pregnant any day – regardless of its date or of the position of the moon in the sky. Several relatively safe days do exist – it is two days before menstruation and two days after graduation. However the menstrual cycle can shift and change due to various stresses, taking certain drugs, diseases of the genitourinary system, etc., so no guarantee in this case can not be.
The use of the calendar method is only useful, if the woman's cycle is stable, otherwise, calculating safe days is virtually impossible. To schedule need to perform entire menstrual cycle for a year, during which it was not used hormonal contraceptive. With the constant onset of menstruation in the same period (assuming minimum deviation) it is possible to start the calculation of the safe period.
To schedule you first need to determine the length of the longest and the shortest menstrual cycle over the counting period. Then from the period with the minimum number of days subtracted by 18 and the result is a day in which the likelihood of pregnancy above all else. To calculate a safe day, we need to subtract 11 from the period of the cycle with the maximum number of days – so this will be the last date in which you need protection and which occurs after a few days, relatively safe for unprotected sex.
From the calendar method has its own characteristics. So, at irregular sexual life, the body can respond to each new sexual act, triggered by unplanned ovulation. The same often occurs when interrupted sexual intercourse – substances in male semen can induce ovulation, resulting in safe days before menstruation are not that. In other words, to avoid an unwanted pregnancy by using the calendar only if a regular sex life and a permanent partner.