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Ovulation calculator
Find your fertile window and the day you probably ovulate, from the first day of your last period and your cycle length. Free online ovulation calculator that lists the next six cycles. It is a calendar estimate, not contraception.
How to calculate your fertile days
- 1Pick the first day of your last period
- 2Enter your cycle length
- 3Adjust luteal phase and period length if you know them
- 4Read the fertile window and the table
- Your fertile window, ovulation day and next period.
What you get
- Dates, not guesses.The result is a date range plus the day ovulation is likely, in your language's date format.
- Six cycles ahead.A table lists period start, fertile window and ovulation for each of the next six cycles.
- Stays on your device.Your dates are worked out in the browser and are not sent anywhere.
What you can do
- Enter a cycle length from 20 to 45 days. The default is 28.
- Change the luteal phase (9 to 18 days) if you know it. The default is 14 days from ovulation to the next period.
- Set the length of your period, from 1 to 10 days.
- See the next period, the ovulation day and the date from which a pregnancy test makes sense.
- If your last period was a while ago, the list starts with the cycle that is running today.
Good to know
- The fertile window is six days: the five days before ovulation, the day itself and the day after. This follows the calendar method.
- It is not contraception and must not be used to avoid pregnancy. Stress, illness and irregular cycles move ovulation.
- A date in the future is rejected, because the tool needs your last period to have started.
Questions
How is the ovulation date calculated?
Ovulation is placed the luteal phase before your next period. With a 28 day cycle and a 14 day luteal phase, that is day 14.
Can I use it if my cycle is irregular?
The result will be less reliable. Use the cycle length you usually have, and treat the dates as a rough guide.
Does it work as birth control?
No. It is a calendar estimate and says so on the tool. Do not rely on it to prevent pregnancy.
Is my data stored?
No. The calculation runs in your browser and nothing is sent to a server.