Ovulation calculator
Ovulation and fertile window calculator
Enter the first day of your last period and your usual cycle length to estimate when you ovulate and your most fertile days.
Updated
Your estimate
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This is an estimate, not a diagnosis or birth control.
How do I work out when I ovulate?
Ovulation usually happens about 14 days before your next period. To estimate it, add your cycle length to the first day of your last period to find your next period, then count back 14 days. Your fertile window is the five days before ovulation plus the day of ovulation. Cycles vary, so treat this as an estimate.
How it's calculated
- Next period = first day of last period + your cycle length.
- Ovulation ≈ next period − 14 days.
- Fertile window = 5 days before ovulation through 1 day after.
- This calendar method assumes regular cycles. Ovulation tests and basal body temperature give a better picture.
Gyne learns your real cycle and adjusts these estimates as you log.
Frequently asked questions
How many days are you fertile?
About six days each cycle: the five days before ovulation and the day of ovulation, because sperm can live up to five days.
Is this calculator accurate with irregular periods?
Less so. With irregular cycles, ovulation tests, cervical mucus and temperature tracking are more reliable. Gyne combines these for you.
Can I use this to avoid pregnancy?
No. A calendar estimate is not birth control. Talk to your doctor about contraception that works for you.
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