Free tool
Fertile Period Calculator
Trying for a baby? Enter the first day of your last period and your usual cycle length — we'll estimate your ovulation day and the fertile window when conception is most likely.
Your cycle details
The first day of bleeding, not the last.
From the first day of one period to the first day of the next.
This calculator gives an estimate based on average cycles. Ovulation can vary with stress, illness and cycle irregularity. If you've been trying for over a year (or 6 months if over 35), speak to a specialist — book a consultation with Dr Chaminda Mathota.
Medical disclaimer: this calculator provides a general estimate only and is not medical advice, diagnosis or treatment. The fertile-period calculator must not be relied on as contraception. Always confirm results with your doctor — see our full disclaimer.
How the fertile window works
Ovulation timing
Ovulation usually happens about 14 days before your next period starts — not 14 days after the last one. That's why cycle length matters.
A six-day window
Sperm can survive up to 5 days, but the egg lives only about 24 hours. The fertile window is the 5 days before ovulation plus ovulation day itself.
Best odds
Intercourse every 1–2 days during the fertile window gives the highest chance of conception — around 25–30% per cycle for healthy couples.
Planning a pregnancy? A pre-conception check-up helps you start on the right foot.
Book a consultation Try the due date calculator