Ovulation Calculator

How this ovulation calculator works

Your ovulation day is estimated by counting back about 14 days from the start of your next expected period. We take the first day of your last period, add your average cycle length to find your next period, then subtract 14 days to land on your likely ovulation day. This "luteal phase" of roughly 14 days is the most consistent part of most cycles, which is why counting backward is more reliable than counting forward.

Your fertile window

The fertile window is the stretch of days when sex is most likely to lead to pregnancy. Because sperm can survive up to about 5 days and an egg lives for around 24 hours, we highlight the 5 days before ovulation plus ovulation day itself — a 6-day window. The two or three days right before ovulation are typically the most fertile of all.

How to use it

1. Pick the first day of your last period on the date field.
2. Enter your average cycle length — the number of days from the start of one period to the start of the next (28 is a common default).
3. Read your estimated ovulation day, fertile window, and next expected period. Results update instantly as you change either value.

FAQ

How do I know my cycle length?

Count from the first day of one period to the first day of the next. If it varies, use an average of your last few cycles. Most cycles run 21 to 35 days.

Is ovulation always on day 14?

No. Day 14 only applies to a textbook 28-day cycle. This tool adjusts by counting back 14 days from your next period, so a longer or shorter cycle shifts ovulation accordingly.

Can I use this to avoid pregnancy?

It is not reliable for contraception. Cycles vary month to month, so use a proven birth-control method instead of these dates.

Are these dates exact?

These are estimates, not medical advice. Ovulation timing shifts with stress, illness, and natural variation — talk to a healthcare provider for personalized guidance.