Enter your last period date and average cycle length to estimate your fertile window, peak ovulation day, and next period — helpful context for those trying to conceive.
Enter the first day of your last period to see your fertile window.
How to use this calculator
Enter the first day of your most recent period and your average cycle length in days. The calculator estimates the 6-day fertile window (the 5 days before ovulation and ovulation day), your peak ovulation day, and the expected start of your next period.
Understanding your result
The fertile window is calculated from ovulation, which is estimated at 14 days before the start of your next period. Fertile days are the 5 days before ovulation through the day of ovulation. These are statistical estimates based on average cycle patterns — actual fertile timing varies between individuals and between cycles.
Disclaimer
Menstrual cycles and ovulation timing vary significantly between individuals and from month to month. These predictions are statistical estimates and should not be used as a sole method of contraception or fertility planning. This is not medical advice. If you are trying to conceive, struggling to conceive, or have concerns about your cycle, consult a gynaecologist or healthcare provider.
Track your fertility in OptiAI
Log your cycle, track your fertile window over multiple months, and manage your fertility journey alongside the rest of your health and life planning in OptiAI.
Frequently asked questions
What is the fertile window?
The fertile window is the span of days in your cycle when conception is possible. Sperm can survive in the reproductive tract for up to 5 days, and an egg can be fertilised for around 12–24 hours after ovulation. This means the fertile window typically covers the 5 days before ovulation and the day of ovulation itself — a total of about 6 days per cycle.
How many days are you fertile each cycle?
Most people have a fertile window of approximately 6 days per cycle — the 5 days leading up to ovulation and ovulation day itself. The peak fertile day is typically the day before and day of ovulation. Timing varies between cycles and between individuals, so these estimates are a helpful starting point, not a precise schedule.
Is this medical advice?
No. This calculator provides estimates for informational purposes only. Always consult a qualified healthcare professional before making decisions about your health, contraception, or fertility planning.
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