Ovulation & Fertile Window Calculator
Estimate your ovulation day and fertile window from your cycle.
days
How it works
Ovulation usually happens about 14 days before the next period. The fertile window covers the 5 days before ovulation plus the day after. This is an estimate for regular cycles and is not birth control. Speak to a doctor about irregular cycles. Example: with the default values, estimated ovulation day comes to Sun Oct 04 2026.
FAQ
Is this calculator free?
Yes. No signup is needed and nothing you enter is stored.
Is the result exact?
Results are rounded for display. For financial, medical, or legal decisions, confirm with a professional.
Do my numbers leave my device?
No. The calculation runs in your browser.