Ovulation calculator
This calculator is an estimate based on averages. It is not reliable as contraception and cannot confirm ovulation.
🔒 Calculated locally — your dates never leave your device
The calendar marks your estimated fertile window (the 5 days before ovulation plus ovulation day and the day after). Sperm can survive up to about 5 days, while an egg lives roughly 12–24 hours — that is why the window opens before ovulation.
Calendar estimates work best with regular cycles. Stress, illness, travel and weight changes can shift ovulation, so treat the result as a guide, not a guarantee. For higher precision, combine it with ovulation tests (LH strips) or basal body temperature.
Frequently asked questions
How accurate is an ovulation calculator?
It gives a statistical estimate. Real ovulation can shift by several days even in regular cycles, so use it as a starting point and confirm with LH tests or body signs (cervical mucus, basal temperature) if timing matters.
When am I most fertile?
The two days before ovulation and ovulation day itself carry the highest chance of conception. The full fertile window spans about 6 days.
Can I use this if my cycles are irregular?
Calendar methods become unreliable with irregular cycles. If your cycle varies by more than a few days, ovulation tests or a consultation with a doctor will serve you better.
Related reading
Ovulation discharge: what it looks like
Near ovulation your cervical mucus usually becomes clear, slippery and stretchy — much like raw egg white. This “egg-white” discharge signals your most fertile days; it appears for a few days, peaks around ovulation, then dries up.
Read more →Ovulation cramps (mittelschmerz)
Many people feel a mild, one-sided ache low in the abdomen around ovulation — called mittelschmerz (German for “middle pain”). It usually lasts from a few minutes to a couple of days and is generally harmless.
Read more →Cervical mucus: a guide to each stage
Cervical mucus changes through your cycle as estrogen rises and falls. Just after your period it is scant or sticky; as you approach ovulation it becomes creamy, then clear, slippery and stretchy like egg white — the sign of your most fertile days. After ovulation it turns thick and dries up.
Read more →Symptoms by DPO (7–14)
What each day past ovulation can feel like
Read more →References
- ACOG – Fertility Awareness-Based Methods of Family Planning (acog.org)
- NHS – How can I tell when I am ovulating? (nhs.uk)
- Wilcox AJ et al. Timing of sexual intercourse in relation to ovulation. N Engl J Med 1995.