Ovulation Calculator

How Ovulation Is Estimated

For a regular cycle: ovulation ≈ next period − 14 days, and the fertile window runs from about 5 days before ovulation through the day of ovulation. Next period = first day of last period + cycle length.

⚠️ This tool is for family-planning awareness, not contraception. Calendar methods are unreliable because ovulation can shift. For important decisions use a proven method of contraception or speak to your GP.

Frequently Asked Questions

How is ovulation estimated?

Ovulation typically occurs about 14 days before your next period. The calculator adds your cycle length to the first day of your last period to find the next period, then counts back 14 days.

What is the fertile window?

It is the span when conception is most likely — roughly the 5 days before ovulation plus the day of ovulation, because sperm can survive several days and the egg lives about 24 hours.

Can I use this for contraception?

No. Calendar-based estimates are not reliable contraception. Ovulation timing varies with stress, illness and hormones. Use a proven method of contraception if you are avoiding pregnancy.

When are the best days to conceive?

Having sex during the fertile window — especially the two to three days leading up to and including ovulation — gives the highest chance of conception.