Ovulation calculator
Enter the first day of your last period and your cycle length. The tool shows the next 3 cycles.
Please note
This tool gives an estimate only. It is not medical advice. It is not birth control. Ask your doctor or midwife about your own care.
Result
Enter a date to see your result.
How to use it
- Enter the first day of your last period.
- Choose your cycle length, from 21 to 45 days.
- Read the ovulation day and the fertile window of each cycle.
- Read the due date for a pregnancy that starts in that cycle.
Questions
How does the tool work out the ovulation day?
It counts back 14 days from your next period. With a 28 day cycle, the ovulation day is day 14.
What is the fertile window?
It is the 5 days before ovulation and the day of ovulation. This is 6 days. A study found that pregnancy was possible only in these days.
Can I use this tool as birth control?
No. The tool gives an estimate only. The ovulation day can change from cycle to cycle. This tool is not birth control.
What is the due date in each cycle?
It is the due date if a pregnancy starts in that cycle. The tool adds 266 days to the estimated ovulation day.
What if my cycle length changes?
Cycles are not the same every month. Use the average length of your last cycles. Ask your doctor or midwife if you have questions.