Ovulation Calculator – Find Your Fertile Window

Ovulation Calculator — When Am I Most Fertile?

If you are trying for a baby, knowing your most fertile days can help. Enter your last period and cycle length to estimate them.

Last updated 10 October 2026 · Written for patients in Ireland

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How ovulation is estimated

Most people ovulate about 14 days before their next period starts. The fertile window is the five days before ovulation and the day after. This calculator uses your cycle length to estimate those days for the next three cycles.

Tips when trying to conceive

Have sex every two to three days through your cycle
Take folic acid daily before and during early pregnancy
Stop smoking and keep alcohol low
A healthy weight can improve fertility for both partners

When to talk to a doctor

See a doctor if you have been trying for a year (or 6 months if you are 35 or over), if your periods are irregular or absent, or if you have a condition that may affect fertility.

Frequently asked questions

Can I use an ovulation calculator as contraception?

No. Ovulation can vary from cycle to cycle, so this is not a reliable way to avoid pregnancy.

What if my cycle is irregular?

The estimate will be less reliable. Ovulation test kits or a chat with a doctor can help.

Official sources and further reading

HSE: trying for a baby

This page is general information for patients in Ireland, not a diagnosis or personal medical advice. If you are worried about your health, speak to a doctor. In an emergency call 112 or 999.

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