Period Calculator
Understanding your menstrual cycle helps you plan ahead and recognise changes in your health. Enter the first day of your last period and your average cycle length to get predictions for the next 6 months, including expected period start dates, fertile windows, and estimated ovulation days.
Typical range: 21–45 days (average is 28)
Typical range: 2–8 days (average is 5)
How period calculation works
Your menstrual cycle is counted from the first day of one period to the first day of the next. The average cycle is 28 days, but cycles anywhere from 21 to 45 days are considered normal.
Next period: Calculated by adding your average cycle length to the first day of your last period.
Ovulation: Estimated to occur 14 days before your next period starts. This is based on the luteal phase, which is relatively consistent at about 14 days for most women.
Fertile window: Spans from 5 days before ovulation to 1 day after. Sperm can survive in the reproductive tract for up to 5 days, so the fertile window begins before ovulation occurs.
Cycle Tracking Essentials
Period tracking apps, menstrual cups, heating pads, and supplements to support your cycle.
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Frequently Asked Questions
How is my next period calculated?
What is a normal menstrual cycle length?
When is my fertile window?
Can stress affect my cycle?
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