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Ovulation calculator and fertile days
Enter the first day of your last period and the usual length of your cycle to estimate ovulation day, the fertile days and the date of the next period, also for the next three cycles. It is a calendar estimate: it is not a method of contraception and it becomes unreliable with irregular cycles.
- Free with an account
- Next 3 cycles
- 21- to 45-day cycle
- Enter your last period
- Set your cycle
- Check your dates
HOW TO USE IT
Three steps.
Enter your last period
The first day of bleeding of your last period.
Set your cycle
The days from the start of one period to the start of the next. If it varies, use your average.
Check your dates
You will see the estimated ovulation, the fertile days and the next period for this cycle and the next three.
NEXT STEP
Keep going with these tools
Ovulation calculator: common questions
How is ovulation worked out?
It is estimated 14 days before the next period. The fertile days run from 5 days before ovulation to 1 day after, because sperm can live for several days.
Can I use it to avoid pregnancy?
No. It is a calendar estimate and ovulation can come earlier or later. It is not a method of contraception: ask a healthcare professional.
Does it work if my cycles are irregular?
It becomes unreliable, because it assumes a fixed cycle. Ovulation tests or follow-up with a professional give more precise information.
Is my data sent to a server?
No. The numbers, dates and names you type are calculated in your browser and are not sent to Cocuyo or to any third party.
Is it really free?
Yes. You can try it before signing up; to keep using it, we ask for a free account, with no subscription. It uses no credits and does not count toward your 30 welcome uses: it has no usage cap.
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