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Period & Ovulation Calculator

Predict your next period, fertile window and ovulation day for the next three cycles.

Your cycle

First day of your last period

Cycle lengthdaysDay 1 to next day 1Period lengthdays

Luteal phasedaysLeave at 14 unless you track ovulation

Pick the first day of your last period.

How it's calculated

Ovulation is estimated as your next period minus the luteal phase (14 days by default, adjustable from 10 to 16).
The fertile window is the 5 days before ovulation plus ovulation day and the day after — sperm can live up to 5 days, an egg about 1 day.
Future periods are predicted by adding your cycle length to the first day of your last period.

Sources

Questions people ask

When am I most fertile?

In the 2–3 days before ovulation and on ovulation day. The calculator highlights the full 7-day window.

Can I use this as contraception?

No. Calendar predictions can be off by several days because ovulation shifts with stress, illness and travel. Use a reliable contraceptive method.

What is a normal cycle length?

21 to 35 days in adults. Cycles regularly outside this range are worth checking with a gynaecologist — PCOS and thyroid problems are common causes in India.

What is the luteal phase?

The days between ovulation and your next period — usually 12–14. Leave it at 14 unless you track ovulation with test strips or temperature.

This website provides general educational information and is not a substitute for professional medical diagnosis, treatment or emergency care. Always consult a qualified healthcare professional.