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.