Ovulation Calculator

Find your fertile window and predicted ovulation day based on your cycle — a simple estimate to plan around.

How to Use This Calculator

Enter the first day of your last period and your average cycle length. Sperm can survive up to five days, so the fertile window starts well before ovulation day.

To conceive, having intercourse during the fertile window maximizes your chances.
To avoid pregnancy, this is not a reliable method — ovulation can shift from cycle to cycle.
Combine with cervical mucus or temperature tracking for better accuracy.

Frequently Asked Questions

How accurate is an ovulation calculator?

It is a good estimate for regular cycles but can't predict ovulation shifts. Apps that use BBT and LH tests are more precise.

Can I get pregnant outside the fertile window?

Only if ovulation itself shifts. Sperm survive up to 5 days and the egg about 24 hours, which is why the window matters.

My cycle is irregular — what now?

Irregular cycles make calendar prediction unreliable. Track symptoms and use ovulation test strips.

Is this medical advice?

No. For fertility concerns, consult a healthcare provider.

Practical Example

Suppose your last period started on August 1 and your cycle is 28 days:

Ovulation ≈ day 14 → August 14–15
Fertile window ≈ August 10–15 (sperm survival + egg life)
Next period expected ≈ August 29

What Your Results Mean

Ovulation day — when the egg is released, roughly 14 days before your next period.
Fertile window — the days intercourse can lead to conception.
For regular cycles, planning around the window maximizes chances; irregular cycles need more precise tracking.