Determining the Fertile Window using the Sympto-thermal Method of Fertility Awareness
This person's fertile phase begins on Cycle Day 8 when cervical fluid production begins. Since this person experienced a SUDDEN temperature shift on Day 16, the Peak Day Rule is satisfied on the 3rd day after their Peak Day. The Temperature Shift Rule is satisfied on the 3rd consecutive day of a basal body temperature that is above the coverline, since that third temperature is at least 0.3 °F (0.15 °C) above the coverline. The fertile phase ends in the evening on Cycle Day 18, since that is when both the Peak Day Rule and the Temperature Shift Rule are satisfied.
Learn the rules of the sympto-thermal method of fertility awareness.