Built for Women,
Designed for Privacy
Calculate Periods was born from a simple belief: your menstrual health data is deeply personal, and no one else should have access to it — not advertisers, not data brokers, not us.
Try the Free CalculatorAbsolute Privacy
Every byte of your cycle data is stored exclusively in your browser's local storage. We have no server, no database, and no access to your health information — ever.
Always Free
No subscriptions, no premium tiers, no hidden fees. The full period calculator, cycle insights, ovulation tracker, and symptom logger are free — no account required.
Science-Based
Our cycle predictions are based on established menstrual cycle science — accounting for all four phases, ovulation timing, fertile windows, and irregular cycle support.
Our Mission
Menstrual health tracking apps have proliferated in recent years — but so have stories of these apps selling intimate health data to third parties, insurance companies, and employers. We believe that is wrong.
Calculate Periods was created as a direct response to that problem. By running entirely in your browser with zero server-side processing, we've made it technically impossible for us to access your data — even if we wanted to.
Our goal is simple: give every person with a menstrual cycle access to a powerful, accurate, beautiful tracking tool — without asking them to sacrifice their privacy to use it.
Trusted by thousands
Used daily by people tracking their cycles without sharing a single byte of health data with us.
Zero data collection
No sign-up. No tracking. No selling your data. Your period is your business.
Works everywhere
Desktop, tablet, or mobile — no app download required. Just open and start tracking.
What We Offer
Period Predictions
Accurate next-period forecasts up to 6 months ahead based on your cycle length.
Ovulation Tracking
Identify your fertile window and ovulation day to support family planning.
Cycle Insights
Visual analytics of your cycle patterns, phase lengths, and trends over time.
Symptom Logger
Log mood, flow intensity, and physical symptoms to find patterns in your cycle.
Medical Disclaimer
Calculate Periods is an informational tool only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your menstrual health or any medical condition.
Ready to start tracking?
No sign-up. No subscription. Just you and your cycle data.
Open the Free Calculator