Ovulation Calculator

Enter the first day of your last period and your cycle length. See your ovulation day, fertile window and next period for three cycles ahead.

What is ovulation and when does it happen?

Ovulation is when a mature egg is released from the ovary. Cycle length varies from person to person, but the time after ovulation, called the luteal phase, is fairly steady at 12 to 16 days for most. That is why ovulation is estimated by counting back from your next period rather than forward from the last one.

Example: with a 30 day cycle and a period that started on March 1, your next period is due around March 31. Counting back 14 days puts ovulation around March 17 and your fertile window from March 12 to 18.

Signs of ovulation

  • Cervical mucus: it increases and becomes clear and stretchy, like raw egg white.
  • Basal body temperature: your waking temperature rises about 0.2 to 0.5 °C (0.4 to 1 °F) after ovulation and stays up until your period.
  • LH tests: ovulation tests detect the LH surge 24 to 36 hours before ovulation.
  • Mild pelvic pain: some feel a brief one sided twinge at ovulation.

Tracking these signs together confirms the calendar estimate. HeyMom's ovulation test tracker and basal temperature chart are built for this.

Frequently asked questions

How do I calculate my ovulation day?

Ovulation usually happens about 14 days before your next period starts. In a 28 day cycle that is day 14, counting the first day of your period as day 1. In a 32 day cycle it moves to around day 18. The calculator uses your cycle length to apply this rule.

What is my fertile window?

Sperm can survive up to 5 days in the body, while an egg lives about 12 to 24 hours. Your fertile window is the 5 days before ovulation plus ovulation day. Chances are highest in the 2 days before ovulation and on the day itself.

Can I predict ovulation with irregular periods?

Calendar estimates work best with regular cycles. If your cycle length changes by more than a few days, the estimate becomes less reliable. Ovulation tests, basal body temperature and cervical mucus tracking give clearer signals.

When should I take a pregnancy test?

Home pregnancy tests are most reliable from the day your period is due, about 14 days after ovulation. Testing earlier may give a false negative because hormone levels can still be too low.

Can I use this for birth control?

No. Calendar estimates are only predictions. Ovulation can shift by several days with stress, illness or travel. Talk to your doctor about a reliable contraception method.