After twelve consecutive cycles (cycles with ovulation) you can determine the earliest temperature shift you had within these twelve cycles. From this day you subtract eight days. You now can assume infertility until this day each cycle, however, only if you are not experiencing cervical fluid before reaching that day.
Exception: If during one of those first twelve cycles your temperature shift occurs before day thirteen of your cycle, you immediately have to use the Minus 8 Days Rule to heighten safety.
Note: For women in perimenopause this rule never applies, they should never assume infertility around the beginning of the cycle. You can enable a 'Menopause' mode in the evaluation settings.
We do not guarantee the method of birth control or pregnancy achievement as described on this web site.