How to use the Ovulation Calculator
- Enter the first day of your last period.
- Enter your average cycle length (usually 21–35 days).
- See your fertile window, ovulation day and next period for three cycles.
About this tool
Ovulation usually happens about 14 days before your next period starts. Because sperm can survive up to five days, the fertile window covers the five days before ovulation plus the day itself.
Cycles vary from month to month, so this is an estimate. Ovulation test kits, basal body temperature and cervical mucus changes can help confirm ovulation. This calculator should not be used as a method of birth control.
Frequently asked questions
When am I most fertile?
The two to three days before and including ovulation.
Can I use this if my cycles are irregular?
Results are less reliable with irregular cycles. Consider ovulation tests or speaking with a doctor.
Can this be used for contraception?
No — calendar estimates are not reliable enough for birth control.