How does the counting days method work?
With the counting days method, you do not have sexual intercourse during any time that you might be fertile. This method can be used only if you have regular cycles that last between 26 and 32 days. This means that the time from the first day of one monthly bleeding, to the first day of your next monthly bleeding, must be at least 26 days, and no more than 32 days.
This method will usually work if you have nearly the same number of days from one monthly bleeding to the next (regular cycles). But if you have one cycle of a different length, you can easily get pregnant. It is common for a woman to have a cycle of a different length when she is sick or feeling a lot of stress. So if you are sick or feeling stress, it will be best for you to use a different family planning method until you are well and your cycle is normal.