1. Natural family planning in which ovulation is assumed to occur 14 days before the onset of a period (the fertile period would be assumed to extend from day 10 through day 18 of her cycle)
   "They relied on the calendar method of birth control for contraception, but it proved less effective than other methods";
   - rhythm method of birth control, rhythm method, rhythm, calendar method

Derived forms: calendar methods of birth control

Type of: natural family planning