Period Calculator
Predict your next period, ovulation day, and fertile window
First Day of Last Period
Cycle Length (days)
Typical range: 21–35 days (average 28)
Period Duration (days)
Typical: 3–7 days
Important Note
This calculator gives estimates based on regular cycles. Cycle length varies naturally. For medical advice, consult a healthcare professional.
Next Cycle Predictions
Next Period Starts
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Period Ends
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Ovulation Day
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Fertile Window
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Next 3 Cycles
| Cycle | Period Dates | Ovulation |
|---|---|---|
| Enter your last period date above | ||
Understanding Your Menstrual Cycle
A typical menstrual cycle is 21–35 days, measured from the first day of one period to the first day of the next. Ovulation usually occurs about 14 days before your next period (not 14 days after the last — this is a common misconception).
The fertile window spans 5 days before ovulation to 1 day after, since sperm can survive up to 5 days in the reproductive tract. Tracking your cycle helps you plan or identify irregular patterns worth discussing with a doctor.
lightbulb Example
Last period: 1 May, cycle: 28 days
1Next period: 29 May
2Ovulation: 15 May (28−14)
3Fertile: 10–16 May
✓ Based on a regular 28-day cycle