Ovulation & Fertility Calculator
Calculate Your Fertile Window
Enter two details — get your complete cycle picture
Please select a date to continue.
The first day you had full flow
Please select your cycle length.
Day 1 of this period to day 1 of your next
Fertile Window
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Best days to conceive
Peak Ovulation
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Highest chance of conception
Next Period Due
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Estimated start date
Your Cycle at a Glance
Having intercourse every 1–2 days during your fertile window gives you the best chances of conceiving.
How Does the Calculator Work?
Ovulation typically occurs 14 days before your next period. This calculator uses your last period date and average cycle length to pinpoint that window accurately.
Your fertile window covers the 5 days before ovulation plus ovulation day itself — because sperm can survive in the reproductive tract for up to 5 days, while an egg is viable for just 12–24 hours after release.
For the most accurate picture, combine this calculator with BBT tracking and cervical mucus observation — especially if your cycle tends to vary month to month.
Frequently Asked Questions
Your fertile window is the span of days in your cycle when pregnancy is possible — the 5 days before ovulation plus ovulation day itself. Your two most fertile days are the day before and the day of ovulation.
It is very unlikely, but cycles vary. Ovulation can shift due to stress, illness, or lifestyle changes. Pairing this tool with BBT tracking and ovulation test strips gives you the most reliable picture.
Use your average cycle length from the past 3–6 months. If your cycle varies significantly, speak to your doctor or gynaecologist — they may recommend additional ovulation-tracking methods tailored to you.
Wait until the first day of your missed period, or at least 14 days after your estimated ovulation date. Testing too early risks a false negative — hCG levels may not yet be detectable.
It is a reliable guide based on established cycle science, but it is not a medical device. Results are estimates — individual cycles vary. Always use alongside professional medical advice for important fertility decisions.
This tool is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider for personalised fertility guidance.