Ogino method

The Ogino method is based on the hypothesis that ovulation occurs each month on the same date (on average, 12 to 15 days from the first day of the last menstrual period, for a 28-day cycle). In practice, this method needs to be studied for at least 6 continuous cycles in order to be able to then subtract days identified as fertile.

Note: irregular cycles and occasionally unpredictable ovulation make this method relatively ineffective, and it requires long periods of sexual abstinence.