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Period Calculator – Predicts the start of the next menstrual period...

The Period Calculator predicts the start of the next menstrual period based on average cycle length. This Period Calculator uses an established clinical or fitness formula to give you a personalised estimate in seconds. Results are for educational reference — for specific health decisions, discuss with your doctor.

The formula behind this calculator: Adds the average cycle length in days to the start date of the last period. As a practical example: A period starting June 1 with a 28-day cycle predicts the next period around June 29. All results are calculated instantly in your browser — no data is stored or transmitted.

Period Calculator FAQ

What does the Period Calculator calculate?

Predicts the start of the next menstrual period based on average cycle length.

Should I use metric or imperial units?

Either — the calculator accepts both. Metric values (kg, cm) tend to have simpler conversion paths in the underlying formulas.

Can this calculator track my progress over time?

This tool doesn't store data between sessions. For tracking, record results manually or use a health app alongside this calculator.

Does this work on mobile?

Yes — fully responsive and optimised for smartphones, tablets, and desktop browsers.