❤️ Free Calculator
Period Calculator
Predict your next period date, fertile window, and ovulation day. Track up to 6 future cycles. Completely private — nothing is stored.
days
days
Ovulation Day
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~14 days before next period
Fertile Window
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5 days before ovulation + ovulation day
Period End Date
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Estimated based on duration
Cycle Length
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Normal range: 21–35 days
Next 6 Cycle Predictions
⚕️ This calculator is for informational purposes only. Menstrual cycles vary. Consult a healthcare provider for medical advice, family planning, or fertility concerns.
What This Calculator Tracks
Next Period Date
Predicts when your next period will start based on your last period and cycle length.
Fertile Window
Shows the 6-day window when conception is most likely — 5 days before ovulation plus ovulation day.
6-Cycle Forecast
Predicts the next 6 period start dates, ovulation days, and fertile windows so you can plan ahead.
100% Private
No data is stored or sent anywhere. All calculations happen locally in your browser only.
Frequently Asked Questions
Add your cycle length to the first day of your last period. For example, if your last period started March 1 and your cycle is 28 days, the next period is expected March 29. This calculator does this automatically for 6 cycles ahead.
Ovulation typically occurs 14 days before your next period. The fertile window is the 5 days before ovulation plus ovulation day. For a 28-day cycle, this is usually around days 10–15 of your cycle (counting from period start).
A normal menstrual cycle ranges from 21 to 35 days. The average is 28 days. It's normal for cycle length to vary by 1–3 days each month. Significant changes in cycle length or regularity should be discussed with a doctor.
Common reasons for a late period include stress, significant weight change, illness, excessive exercise, hormonal imbalance (e.g. PCOS), travel, or pregnancy. A period is typically considered late after 5 or more days past the expected date. Take a pregnancy test if relevant.
This is an estimation tool based on average cycle assumptions. For conception planning or contraception, work with a gynecologist who can use more precise methods such as basal body temperature tracking, LH surge testing, or ultrasound monitoring.