Category
What the hormones are doing, why cycle length moves, and how predictions are made.
27 July 20267 min read
Your tracker is not wrong, it is averaging. Most of a prediction's error comes from the follicular phase, the variable half of the cycle, where delayed ovulation pushes the whole date back.
27 July 20267 min read
Most people picture the cycle as bleeding, and not bleeding. It actually runs through four phases, and the second half keeps far steadier time than the first.
27 July 20267 min read
Clinical guidance has treated the menstrual cycle as a fifth vital sign since 2006, reaffirmed as recently as 2025, with a reference range and a list of patterns worth a GP visit.
