About Periodly
Our mission
Periodly exists to give anyone a simple, private period calculator — free of accounts, ads disguised as features, or data harvesting. Enter a few dates, get an accurate prediction, and move on with your day.
Why Periodly exists
Most period tracker apps ask you to create an account and hand over detailed health data before you can see a single prediction. We built Periodly as the opposite: a calculator that works instantly, in your browser, with nothing stored on a server.
How the calculator works
You tell us the first day of your last period, your average cycle length, and your period length. From there we estimate your next period by adding your cycle length to that start date, place ovulation around 14 days before your next predicted period, and mark a fertile window from five days before ovulation to one day after. If you mark your cycles as irregular, we average your recent cycle lengths and widen the prediction into a realistic range instead of a single date.
Our privacy promise
No accounts. No servers storing your health data. Every calculation runs locally in your browser. The only exception is an optional, consent-gated local-storage save of your last inputs purely so the form remembers them on your next visit — and that never leaves your device either.
Editorial and medical review
Content on Periodly is reviewed for medical accuracy by [Reviewer Name, credentials — e.g. OB-GYN / RN placeholder]. We also cite leading medical organizations throughout our content, including: