Period & Ovulation Calculator
Estimate your next periods, ovulation day and fertile window with a colour-coded calendar
Cycle length counts from the first day of one period to the day before the next. The luteal phase is the time from ovulation to your next period; 14 days is the usual starting point.
Please read
Estimates only. This is not birth control and not medical advice. Cycles vary, so dates can be off by days. See a doctor or nurse about irregular cycles, very painful or heavy periods, or any concern.
Enter the first day of your last period to see your dates.
About Period & Ovulation Calculator
Estimates your next periods, your likely ovulation day and your fertile window from the first day of your last period, your usual cycle length, how long your period lasts and, if you know it, your luteal phase. It also shows the day to take a pregnancy test if your period is late, and a colour-coded month calendar.
Enter the first day of your last period and your average cycle length. Change the period length or luteal phase if yours differ from the defaults. If your cycles vary, add your shortest and longest cycle to get a range of dates instead of one date. Save the dates to your calendar (.ics), or as a PDF or text summary, or copy, share or print them. Reading results never uses a trial use; taking them away uses 1 per visit.
These are estimates from the calendar method, so treat them as a guide, not a guarantee. They are not birth control. Cycles change with stress, illness, travel and age. If your cycles are very irregular, very painful or heavy, or you have any concern, talk to a doctor or nurse.
- Can I use this as birth control?
- No. It estimates ovulation from your average cycle, and real cycles vary from month to month, so the dates can be off by days. It is not birth control and not medical advice.
- What should I enter if my cycles are irregular?
- Tick "My cycle length varies" and enter your shortest and longest cycle. Every date then becomes an earliest-to-latest range, and the ranges get wider for later cycles. If your cycles are very irregular, talk to a doctor or nurse.
- Is anything I enter saved?
- No. Your dates stay in this page and are not stored or sent anywhere. Saving the calendar file or summary uses one trial use.
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