How the ovulation calculator works
Ovulation usually happens about 14 days before your next period — not necessarily on day 14. The time from ovulation to your period (the luteal phase) is fairly constant at 12–16 days, while the first half of the cycle varies. So with a 28-day cycle you’d ovulate around day 14, but with a 32-day cycle around day 18.
Your fertile window
Sperm can survive up to about five days, and an egg lives 12–24 hours after ovulation. Your fertile window is therefore the five days before ovulation plus ovulation day itself. The two to three days before ovulation have the highest chance of conception.
Signs of ovulation
- Cervical mucus becomes clear, slippery and stretchy, like raw egg white.
- Ovulation tests (LH strips) turn positive 24–36 hours before ovulation.
- Basal body temperature rises slightly (about 0.5°F / 0.3°C) after ovulation.
- Some people feel mild one-sided pelvic pain (mittelschmerz).
Limits of calendar methods
Calculators assume regular cycles. Stress, illness, travel, breastfeeding and conditions like PCOS can shift ovulation. If your cycles vary by more than a few days, combine the calendar with ovulation tests or temperature tracking. This calculator should not be used as birth control. If you’ve been trying for 12 months (or 6 months if you’re 35 or older) without success, talk to a doctor.
Already pregnant? Estimate your due date with the due date calculator.
Frequently asked questions
When do I ovulate?
About 14 days before your next period. With a 28-day cycle, around day 14.
What are my most fertile days?
The five days before ovulation and ovulation day, especially the two days before.
Can I get pregnant right after my period?
It’s possible with short cycles, because sperm can survive up to five days.
Is an ovulation calculator accurate?
It’s an estimate for regular cycles. Ovulation tests give more precise timing.