Ovulation Calculator
Estimate your ovulation day, fertile window and next period from the date of your last period and your cycle length.
How the ovulation calculator works
Most people ovulate about 14 days before their next period begins. With a 28-day cycle, that is around day 14; with a 32-day cycle, around day 18. Your fertile window is the five days before ovulation and the day itself, when sex is most likely to lead to pregnancy.
Frequently asked questions
How is ovulation calculated?
Ovulation usually happens about 14 days before your next period starts. The calculator subtracts 14 days from your expected next period to estimate ovulation.
What is the fertile window?
The fertile window is the 5 days before ovulation plus the day of ovulation, because sperm can survive up to about 5 days and an egg lives for about a day.
How accurate is an ovulation calculator?
It gives an estimate based on average cycles. Cycles vary, especially if they are irregular, so ovulation tests or tracking body temperature can give more personal information.
Can I use this as birth control?
No. Calendar estimates are not reliable enough to prevent pregnancy. Talk to a doctor or nurse about contraception.
When to talk to a doctor
- Your cycles are shorter than 21 days, longer than 35 days, or very irregular
- You have not conceived after 12 months of trying (6 months if you are 35 or older)
- You have very painful or heavy periods, or bleeding between periods
These dates are estimates for general information only. They are not medical advice and must not be used as contraception.
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