Ovulation Calculator
Predict your ovulation day, most fertile days and next period from your last period date and average cycle length, for the next three cycles.
How the fertile window is predicted
In a typical cycle, ovulation happens about 14 days before the next period — the second half of
the cycle (the luteal phase) is fairly constant, while the first half varies with cycle length. For a cycle of
C days starting on your period's first day:
Ovulation ≈ cycle start + (C − 14) days · fertile window = ovulation − 5 days to ovulation + 1 day
The window is six to seven days wide because sperm can survive up to five days waiting for the egg, and the egg
itself remains viable for about 24 hours after release. The calculator projects your next three cycles so you can
plan ahead.
Worked example
Last period started 1 July 2026, 28-day cycle: ovulation is expected around 15 July,
with the fertile window from 10 to 16 July. The next period would start 29 July, putting the following ovulation
around 12 August (fertile 7–13 August).
Signs that ovulation is near
- Cervical mucus becomes clear, slippery and stretchy — like raw egg white.
- LH surge — ovulation test strips turn positive 24–36 hours before ovulation.
- Basal body temperature rises by about 0.3–0.5 °C just after ovulation.
- Some people feel mittelschmerz — a mild, one-sided lower-abdominal ache.
The irregular-cycle caveat
Calendar math assumes your next cycles will match your average. If your cycle length varies by more than a few
days month to month, the predicted windows can miss the real one entirely. In that case, use these dates as a
rough guide only and rely on body signs and ovulation tests — and note that calendar prediction is never a
reliable form of contraception.
Frequently asked questions
When am I most fertile?
The two to three days ending on ovulation day carry the highest chance of conception. The full fertile window is about six days: the five days before ovulation (sperm survive that long) plus roughly a day after, while the egg is viable.
How is the ovulation day calculated?
Ovulation typically occurs about 14 days before the next period starts, so it is estimated as cycle start + (cycle length − 14). With a 28-day cycle that is day 14; with a 33-day cycle it is day 19.
What are the physical signs of ovulation?
Common signs include clearer, stretchy "egg-white" cervical mucus, a slight rise in basal body temperature just after ovulation, mild one-sided pelvic ache (mittelschmerz), and a positive LH surge on an ovulation test strip 24–36 hours beforehand.
My cycles are irregular — can I still use this?
Calendar predictions are only as regular as your cycles. If they vary by more than a few days, the predicted windows can easily miss the real one — combine the calendar with ovulation test strips, basal temperature or cervical mucus tracking for much better accuracy.
Can I use this as contraception?
No. Sperm survival and natural variation in ovulation timing make calendar-based methods unreliable for preventing pregnancy. Speak to a healthcare provider about effective contraception options.
This tool provides general health information, not medical advice. Consult a healthcare professional before making decisions based on it. Dates are estimates — only an ultrasound can date a pregnancy accurately; always confirm with your healthcare provider.