Menstrual, ovulation, and fertile window estimates with variance aware confidence
Inputs
Enter at least 3 historical period start dates. Best practice is 6 to 12 recent cycles.
Default 14. Allowed range is 11 to 17.
Used to draw the predicted period days.
What happens under the hood
We compute cycle lengths from consecutive period starts. We remove outliers with a 10 percent trim based
on the distribution. We weight recent cycles more heavily, compute a weighted mean and a median, then
blend them for a robust estimate. Standard deviation drives a confidence score and widens the fertile
window when variance grows. Ovulation is predicted as next period start minus luteal length. Fertile
window is ovulation minus 5 days through ovulation day, widened by variance.