Free Period Calculator & Ovulation Tracker
Free Period Calculator & Ovulation Tracker Online (Accurate Cycle Prediction)
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When did your last period start?
The first day of bleeding, not spotting.
Quick pick:
Everything you need to know your cycle
Science-backed estimates, delivered with warmth.
Next Period Date
Accurate prediction based on your personal cycle length.
Ovulation Window
Know when you're most likely to ovulate, personalized to you.
Fertile Window
Your 7-day fertile window, calculated with your luteal phase.
3-Month Forecast
See your next three cycles at a glance with interactive calendar.
100% Private
No account. No tracking. Everything lives in your browser.
Calendar Export
Add your cycle dates to Google, Apple, or Outlook Calendar.
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How Our Free Period Calculator Works
Our free period calculator uses your last period start date and your average cycle length to predict your next period date, ovulation day, and fertile window. Most menstrual cycles range from 21 to 35 days, with 28 days being the most common. Simply enter the first day of your last period and your typical cycle length to get an instant, personalized forecast.
What Is a Fertile Window?
Your fertile window is the 5–7 days each cycle when pregnancy is possible. It includes the day of ovulation and the 5 days leading up to it, since sperm can survive for up to 5 days in the reproductive tract. Our ovulation calculator identifies this window based on your personal cycle length and luteal phase.
Is the Period Calculator Accurate?
Our calculator provides science-backed estimates based on your cycle history. For the most accurate predictions, track 3 or more consecutive cycles. Cycles can vary due to stress, illness, nutrition, or hormonal changes. Always consult a qualified healthcare provider for medical concerns.
100% Private — No Account Needed
All calculations happen directly in your browser. We never store, sell, or share your personal health data. No sign-up, no email, no tracking — just accurate cycle predictions whenever you need them.
Estimates only — not medical advice. Consult a healthcare provider for medical concerns.