Free Carely Tool

Period Calculator (Next Periods & Fertile Window)

Estimate your next three period start dates and your fertile window from your last period and cycle length.

Track your cycle

Your next periods

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This is an estimate, not medical advice. Cycle length and timing vary from month to month — use this as a guide and check with your doctor if you have concerns.

Frequently asked questions

How are my next period dates calculated?

Each estimated start is your last period start plus your cycle length, repeated for the next three cycles.

How accurate is the fertile window?

It is only an estimate — ovulation is assumed about 14 days before the next period. Real timing varies, so confirm with your doctor.