How we estimate ovulation
In most cycles, the time from ovulation to the next period (the luteal phase) is fairly steady at about 14 days, while the first half of the cycle varies more. So we count back from your next expected period:
- Next period = first day of your last period + your cycle length.
- Ovulation = next period - 14 days (or your own luteal phase length).
- Fertile window = the 5 days before ovulation plus ovulation day.
- Most fertile days = the 2 days before ovulation and ovulation day.
If your last period was a while ago, we roll forward by whole cycles and show the windows that are still ahead of you. Want to plan around your periods too? See the period calculator. Already pregnant? Find your due date.
