Ovulation Calculator
Calculate your fertile window and ovulation date based on your cycle length and last period date.
Want to track this over time? bloom is a period tracking app that helps you log cycles and see trends with a privacy-first approach.
How Ovulation Calculation Works
Cycle Length
Your cycle length is the number of days from the first day of one period to the first day of the next period.
Ovulation Timing
Ovulation typically occurs 14 days before your next period, regardless of cycle length.
Fertile Window
Your fertile window includes 5 days before ovulation and the day of ovulation itself.
BBT Chart Example
Use basal body temperature to confirm ovulation after your fertile-window estimate.
Read Guide →Your Privacy is Protected
This calculator runs entirely in your browser. No data is sent to our servers or stored anywhere. Your personal information stays private.
Want More Advanced Tracking?
Try the bloom App
Get personalized cycle predictions, symptom tracking, and birth control reminders with the bloom app.
