Calculate your 6-day fertile window, peak ovulation date, next expected period, and pregnancy test day with our free Ovulation Calculator. Forecast optimal conception probability dates based on your menstrual cycle length with 100% offline privacy.
Choose the first day of your last menstrual cycle using the date picker.
Adjust the average cycle length slider (20 to 45 days, default 28 days).
Instantly view your 6-day fertile window, peak ovulation date, next expected period, and pregnancy test day.
Your personal health measurements and menstrual dates are processed entirely inside your browser using client-side JavaScript. Nothing ever travels over a network to any server — making BunchTool 100% private.
Calculations run locally in real time as you select dates or move the cycle length slider. Fertile dates and milestone projections update instantly without page reloads.
Interactive milestone cards highlighting your optimal 6-day fertile window, peak conception probability days, and early pregnancy test dates.
The Menstrual Cycle consists of two primary phases separated by ovulation: the Follicular Phase and the Luteal Phase (typically 14 days).
The mathematical equation for forecasting ovulation is:
\(\text{Estimated Ovulation Day} = \text{Last Period Date} + (\text{Cycle Length} - 14\text{ days})\)
\(\text{Fertile Window} = \text{Ovulation Day} - 5\text{ days to Ovulation Day (6 Days Total)}\)
Human sperm survives up to 5 days, while an unfertilized egg remains viable for 12 to 24 hours after release. Intercourse during the 3 days prior to ovulation yields peak conception odds.