Ovulation Calculator
Calculate your ovulation date and fertile window based on your menstrual cycle length and last period.
days
Estimated Ovulation
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Fertile Window Start —
Fertile Window End —
Next Period —
How to Use This Calculator
Enter the first day of your last period and your average cycle length (most common is 28 days). The calculator estimates your ovulation date, fertile window, and next period date.
Formula
Ovulation Day = Cycle Length - 14
Fertile Window: 5 days before ovulation to 1 day after
Next Period = LMP + Cycle Length
Fertile Window: 5 days before ovulation to 1 day after
Next Period = LMP + Cycle Length
Example
Example: Last period March 1, 28-day cycle: Ovulation ≈ March 15. Fertile window: March 10-16. Next period: March 29.
Frequently Asked Questions
- Ovulation typically occurs 14 days before your next period. For a 28-day cycle, that's day 14. For a 30-day cycle, it's day 16.
- The fertile window is about 6 days: 5 days before ovulation and the day of ovulation itself. Sperm can survive up to 5 days, while the egg is viable for 12-24 hours.
- This provides estimates based on average cycle patterns. Actual ovulation can vary by several days. For more accuracy, use ovulation predictor kits (OPKs) or track basal body temperature.
- If your cycle varies by more than 7 days, ovulation prediction is less reliable. Track multiple cycles and use the average length, or consult a healthcare provider.