Ovulation Calculator
Find your fertile window and ovulation day for the next three cycles, shown on a colour-coded calendar.
About Ovulation Calculator
This ovulation calculator shows your likely ovulation day, fertile window and next period dates for the next three cycles. Enter the first day of your last period, your average cycle length and how long your period lasts, and the dates appear on a colour-coded calendar.
It is useful when trying for pregnancy, as the fertile window marks the days when conception is most likely, and it also works as a simple period tracker online. Results are estimates and are less reliable with irregular periods, and the tool must not be used as contraception. It is free, needs no sign-up, and your dates stay on your device.
How to use Ovulation Calculator
- Enter the first day of your last period.
- Enter your average cycle length and period length.
- See ovulation, fertile days and next period dates for three cycles on the calendar.
Frequently asked questions
How is ovulation estimated?
Ovulation usually happens about 14 days before the next period starts (the luteal phase is fairly constant). So for a 30-day cycle it falls around day 16.
What is the fertile window?
Sperm can survive up to 5 days and an egg about a day, so the fertile window is the 5 days before ovulation, ovulation day and the day after. The 2–3 days up to ovulation are the most fertile.
Can I use this as contraception?
No. Cycles vary and calendar methods alone have high failure rates. Use ovulation kits or talk to a doctor for reliable planning.
Can I track my period with this calculator?
Yes. Along with ovulation, it shows your next three expected period dates on the calendar, based on your cycle and period length.
What day is the most fertile?
The day of ovulation and the two days before it are usually the most fertile. In a 28-day cycle, ovulation is often around day 14.
Does it work for irregular periods?
It uses your average cycle length, so predictions are less accurate if your cycles vary a lot. Ovulation test kits can help confirm the day.
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