Period Tracker
Estimate your next period, plus an estimated ovulation day and fertile window, from your last period and average cycle length, with a simple calendar. Private by design: nothing leaves your browser.
Your Cycle
By default nothing is saved. If you tick the box, your last start date and averages are kept in this browser's local storage until you delete them.
Health note: Dates shown are estimates only. Cycle timing varies naturally. The ovulation and fertile-window dates are rough calendar estimates, not a prediction of fertility, and must not be used as contraception, to plan or avoid pregnancy, or for medical diagnosis. For concerns about your cycle, please consult a qualified healthcare professional.
Results
Next estimated period
Estimated cycle day today
Upcoming estimated periods
Important: Estimated ovulation and fertile-window dates are for informational purposes only. Actual ovulation can vary. Do not use this tool to prevent pregnancy or make medical decisions.
Estimated ovulation ESTIMATE
Estimated fertile window ESTIMATE
Calculated as about 14 days before your next estimated period, using your average cycle length. The window covers the 5 days before through 1 day after that estimated day. Actual ovulation can vary from cycle to cycle (stress, illness, travel and other factors can shift it), so real fertile days may fall outside these dates. This is not a guarantee of fertile or non-fertile days.
Upcoming estimated fertile windows
How this calculator works
Enter the first day of your last period, your average cycle length (from the first day of one period to the first day of the next) and how many days your period usually lasts. The tracker adds the cycle length repeatedly to estimate the next six start dates and shades the estimated period days on the calendar, which you can move back or forward up to 12 months. It also estimates ovulation as about 14 days before each next estimated period (a typical luteal phase) and marks a fertile window from 5 days before to 1 day after that day. The estimates assume every cycle is identical, so they become less reliable further ahead. Reset clears the form and deletes any saved data.
How are the dates estimated?
The tracker takes the first day of your last period and adds your average cycle length repeatedly to estimate future start dates; each estimated period lasts your average period length. It assumes every cycle is the same length, which real cycles often are not.
How is the ovulation and fertile window estimated?
It uses a simple calendar method: ovulation is estimated at about 14 days before your next expected period, and the fertile window runs from 5 days before to 1 day after that estimated day. These are estimates only. Actual ovulation can vary from cycle to cycle, the dates are not guaranteed, and this tool must not be used as contraception, to prevent pregnancy, or to predict fertility.
Where is my information stored?
Nowhere, unless you tick “Remember on this device”. If you do, your last start date and averages are saved only in this browser's local storage on this device -- never on our servers and never in analytics. Use “Delete my data” (or Reset) to remove it at any time.
When should I talk to a doctor?
Consider speaking to a doctor or gynaecologist if your cycles are regularly shorter than 21 or longer than 35 days, change suddenly, are very painful or heavy, you bleed between periods, or your period stops unexpectedly.
Disclaimer: This tool is for general information only. It is not medical advice. Ovulation and fertile-window dates are estimates only, cannot predict fertility or pregnancy, and must not be used as contraception or to prevent pregnancy. See our Disclaimer and Terms of Use for more detail.