What is the calendar or rhythm method?
The calendar method, or rhythm method, is one of the oldest and most widely practiced methods of fertility awareness, or natural family planning. It is a natural method of birth control.
How does it work?
The calendar-rhythm method is based on three assumptions:
- Ovulation occurs fourteen days before the beginning of menstruation (give or take two days),
- Sperm can live for three days, and
- The egg lives for twenty-four hours.
For a woman with very regular cycles, she only needs to count backwards from the first day of her period to determine the day on which she ovulated. Using this information, she can predict when ovulation will occur the following month and avoid having intercourse around that time -- usually day 14, counted from the first day of her period. As with most natural methods, it is recommended that couples confer with a trained counselor before attempting this method to best determine the fertile window.
How effective is the calendar rhythm method?
Annual Failure Rate
Most women do not ovulate at the same time each month, and no woman's cycles are identical every time. For this reason, the calendar-rhythm method is not considered very effective unless menstrual cycles are always the same number of days. Even then is it very easy to miscalculate if you are not constantly vigilant or well-organized. The annual failure rate for married couples is 20%, with an increase to 29% dating couples, and a huge 38% for cohabiting couples. Because this method is rarely taught, it is not described here in further detail, but you can read more about it at Contraceptive Information Resource. If you are interested in using this type of method, consider the newer standard days method instead, which is easier and more effective.
Side-effects and health risks for the calendar rhythm method
This method of birth control has no side-effects or health risks. The calendar-rhythm method does involve unprotected sex and therefore leaves an individual open to all STDs; it is solely a means of preventing pregnancy.
Considerations for Christians
Most Christians do not have a moral objection to this method of natural birth control, but, with its high failure rate, the calendar-rhythm method can be a risky option. This method is acceptable to the Roman Catholic Church.
- Calendar Method: Contraceptive Information Resource
- Rhythm Method: Epigee Women's Resources (Epigee.org)