Pregnancy & Fertility
Ovulation Calculator
Ovulation usually lands 14 days before your next period. Enter your last period and cycle length to map the window.
Ovulation is the release of an egg, usually about 14 days before the next period. For a 28-day cycle starting on day 1 of menstruation, ovulation occurs near day 14, with the fertile window spanning days 10–15. Dates are estimates — confirm timing with your provider and ultrasound where relevant.
Ovulation ≈ 14 days before next period.
Fertile window: 5 days before + ovulation day.
Egg survives 12–24 hours; sperm up to 5 days.
Calculate Your Ovulation
Ovulation Day
What Is Ovulation?
Ovulation is the release of a mature egg from the ovary. The egg survives 12–24 hours, but sperm can live up to 5 days, which is why the fertile window spans about six days.
The calculator estimates ovulation as 14 days before the next expected period (average luteal phase). Calendar methods are estimates; ovulation tests and BBT charting confirm the real timing.
How It Is Calculated
Ovulation day = cycle length − 14 (luteal phase)
Fertile window = ovulation − 5 days … ovulation + 1 day
Example: Example: LMP Aug 1, 28-day cycle → ovulation ≈ Aug 15, fertile window Aug 10–16
Cycle landmarks (28-day example)
| Event | Day |
|---|---|
| Period starts | Day 1 |
| Fertile window opens | Day 9–10 |
| Ovulation | Day 14 |
| Fertile window closes | Day 15 |
| Next period | Day 28–29 |
Limitations
- Cycle length varies month to month, estimates shift.
- Stress, illness, and travel delay ovulation.
- Not reliable as contraception.
- For irregular cycles, use ovulation predictor kits or BBT.
Sources & Review
References used for this calculator’s formulas and thresholds:
Ovulation FAQ
When am I most fertile?
The two days before ovulation and ovulation day itself, roughly days 12–14 of a 28-day cycle.
How do I know I'm ovulating?
Signs include cervical mucus like egg white, a slight BBT rise, and positive ovulation tests. The calendar is only an estimate.
Can I get pregnant right after my period?
Yes, with short cycles (21–24 days), ovulation can occur soon after bleeding ends, and sperm survive up to 5 days.
What if my cycles are irregular?
Calendar predictions become unreliable. Use ovulation test strips or BBT charting, and discuss irregular cycles with a clinician.
Important disclaimer: Results are educational estimates, not a substitute for professional medical advice. Discuss your numbers with a clinician before acting on them.