Overview of Natural Contraceptive Methods
The calendar method (Knaus-Ogino) is a traditional method of natural contraception, which involves calculating your fertile days based on the length of your cycle. Here you’ll learn how the calendar method works, how to calculate your fertile days, and how reliable it is compared to modern methods such as the the symptothermal method using OvulaRing is true.
In the 1930s, the Austrian physician Knaus and his Japanese colleague Ogino developed the calendar method (Knaus-Ogino) for contraception, which is named after them. It is based on the understanding at the time that ovulation occurs around the middle of the cycle and can theoretically be calculated using a menstrual calendar. For example, the calendar method assumes that, in a 28-day cycle, ovulation occurs on the 15th day of the cycle.
To use the calendar method, a woman must keep a detailed record of her cycle for at least 6 months—preferably a year—and track the length of her cycles. Based on these observations, her fertile and infertile days are calculated using a special formula developed by Knaus and Ogino, taking into account the length of her cycle.
Always subtract 18 days from the shortest cycle length recorded during the observed period. This gives you the first fertile day. Always subtract 11 days from the longest cycle length recorded. The days between these two key dates are then the fertile days. For example, if you have tracked your cycles for six months and your shortest cycle was 27 days and your longest cycle was 33 days, the calculation is as follows:
First fertile day: Cycle length of 27 days – 18 = 9. Last fertile day: Cycle length of 33 – 11 = 22. In this example, the fertile days are therefore from cycle day 9 to 22 (counting from the first day of menstruation). During this period, you should avoid unprotected sex.
The calendar method is a very unreliable form of natural birth control because ovulation and the fertile window cannot be determined with precision. Cycle lengths and patterns vary greatly from woman to woman, and even from cycle to cycle. In addition to a lot of discipline, the calendar method requires, above all, a regular cycle. Cycle fluctuations caused by stress, exercise, illness, and many other factors can affect your cycle and shift your fertile days. The Pearl Index for the calendar method is 9.* This means that 9 out of 100 women will become unintentionally pregnant over the course of a year if the calendar method is used perfectly. The calendar method is therefore one of the least reliable methods of natural contraception and is not recommended as a method on its own.
Instead of the calendar method, we recommend using the symptothermal method to use. OvulaRing can provide you with the best possible support and take care of temperature measurement and analysis.
* Guidelines of the German Society for Gynecology and Obstetrics, July 2004, pro familia.
OvulaRing is a patented method for accurately tracking your cycle. The temperature sensor measures your core body temperature around the clock. This provides you with optimal support for closely monitoring your cycle. OvulaRing is suitable for all cycle types and is as easy to use as a tampon.
The OvulaRing Method
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