September 2026
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Fertility window calculator
See your fertile days based on an ovulation estimate.
Estimate, not a diagnosis. This tool gives an educational estimate based on the numbers you enter. It cannot account for your individual health history — consult a healthcare professional for anything clinical.
Details
The fertile window represents the days when intercourse is most likely to lead to conception, because sperm can survive several days and the egg is viable for roughly 24 hours after ovulation.
Limitations
This is an estimate, not a contraceptive method. Ovulation timing varies between cycles — do not rely on this alone to avoid or achieve pregnancy.
Related reading
- Understanding your cycle phases
- Luteal phase self-care guide
- How age affects fertility
- GLP-1 medications and your period
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Frequently asked questions
What is the fertile window?
The days in your cycle when intercourse is most likely to lead to conception — the five days before ovulation plus ovulation day itself. Sperm can survive up to five days, while the egg is viable for about 24 hours after ovulation.
Which day is the most fertile?
Ovulation day itself and the one to two days immediately before it are generally considered peak fertility, since sperm already present when the egg is released has the best chance of fertilizing it.
Can I use this to avoid pregnancy?
No. This is an estimate based on average timing, not a verified ovulation date, so it is not reliable as a contraceptive method. Ovulation timing varies between cycles.