Yes. However the couples must be highly motivated, well-trained in their method, and committed to avoiding unprotected sex during the fertile time.
The number of days varies based on the woman's cycle length. The average number of days a woman would be considered fertile and would need to abstain or use another method varies between 12 to 18 days dependent on the fertility awareness tracking methodology. To avoid an unintended pregnancy you must use another contraceptive method, such as condoms, during your fertile days.
During monthly bleeding the chances of pregnancy are low but not zero. Bleeding itself does not prevent pregnancy, and it does not promote pregnancy, either. In the first several days of monthly bleeding, the chances of pregnancy are lowest. As the days pass, the chances of pregnancy increase, whether or not she is still bleeding. The risk of pregnancy rises until ovulation. The day after ovulation the chances of pregnancy begin to drop steadily. Some fertility awareness methods that depend on cervical secretions advise avoiding unprotected sex during monthly bleeding because cervical secretions cannot be detected during bleeding and there is a small risk of ovulation at this time.
For many couples, these methods provide reliable information about the fertile days. If the couple avoids vaginal sex, or uses condoms or diaphragm during the woman's fertile time, fertility awareness methods can be effective. Pulling out (using the Withdrawal Method) during the fertile time is less effective and not recommended.
As women and their cycles are different, ovulation varies depending on the length of your cycle, which can range from 21 days up to 35 days.
Let’s have a look at two examples:
Ovulation happens about 14 days before your menstruation starts.
That means: if your average menstrual cycle for example is 28 days, you ovulate around day 14, and your most fertile days are days 12, 13 and 14. If your average menstrual cycle is 35 days ovulation happens around day 21 and your most fertile days are days 19, 20 and 21.
How to count your cycle? The first day of your menstruation is the beginning of a new cycle, hence day 1.