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Period Calculator

Menstrual Cycle Calculator

First Day of Last Period
Cycle Length (days)
Period Length (days)
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For informational purposes only. This tool is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional.
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Pro Tip

Cycle irregularity of a few days is normal. Consult a doctor if cycles are consistently shorter than 21 days, longer than 35 days, or if you experience very heavy bleeding.

Difficulty:Beginner

Did you know?

The word "menstruation" comes from Latin "mensis" (month) and Greek "mene" (moon). Many ancient calendars were based on the lunar cycle (~29.5 days), close to the average menstrual cycle.

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Reviewed May 2026
Used 19K+ times
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