Understanding your result
How ovulation is estimated
Ovulation typically happens about 14 days before your next period (the luteal phase). So:
Ovulation ≈ (last period + cycle length) − 14 days
Fertile window = ovulation day −5 to +1
Fertile window = ovulation day −5 to +1
Sperm can survive up to ~5 days, and the egg for about a day — which is why the fertile window spans several days around ovulation, not just the day itself.
⚕️ A prediction for information only, most reliable with regular cycles. It is not a contraceptive method. For fertility concerns, speak to your GP.
Questions
When am I most fertile?
Your most fertile days are the two to three days leading up to and including ovulation. This tool highlights the whole window and your peak day.
Can I rely on this for contraception?
No. Cycle timing varies and this is a prediction, not a contraceptive method. Use proper contraception if you're avoiding pregnancy.
My cycle is irregular — will it work?
Predictions are less accurate with irregular cycles. Ovulation tests or tracking basal body temperature can help pinpoint your true ovulation.
Sources
Evidence-based · last reviewed July 2026