justyourcalculatorPeriod Calculator
When your next periods are due, with ovulation and fertile days.
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Period Calculator
Predict your next periods and fertile days
Usually 21 to 35 days.
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How the period calculator works
Your next period is expected one average cycle length after the first day of your last one. Cycle length is counted from the first day of one period to the first day of the next; 21 to 35 days is normal for adults.
Ovulation is about 14 days before each period, and the fertile window is the 5 days before ovulation plus the day after. Track a few cycles and use the average for better predictions.
Using and checking your result
Published by JustYourCalculator. Check the units and assumptions above, and compare a known example before relying on the output. Calculations use browser arithmetic and may round displayed values.
This tool provides an estimate, not a diagnosis, treatment plan or individualized medical advice. Population formulas may not fit children, pregnancy, athletes or people with health conditions. Discuss health decisions with a qualified clinician.
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