Ovulation calculator
Enter the first day of your last period and your usual cycle length. The page estimates your ovulation day, your fertile window and your next period for the coming cycles.
- Fertile window, 3 cycles
- Free, no sign-up
This is a standard estimate to plan with. It is general information, and your doctor is the right person for medical advice.
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How to use it
- Enter the first day of your last period.
- Enter your usual cycle length, and your luteal phase if you know it.
- Read the fertile window and ovulation date for the next three cycles.
How the dates are estimated
Ovulation usually happens about 14 days before the next period starts, the length of the luteal phase. The page counts back from your next expected period to find the likely ovulation day. The fertile window covers the five days before ovulation and the day after, because sperm can live for several days.
Cycles vary, so the dates are an estimate. Ovulation tests, basal body temperature and changes in cervical mucus can pinpoint ovulation more closely. If your cycles are very irregular, or you are trying to conceive without success, talk to your doctor.
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Questions
When am I most fertile?
In the two or three days up to and including ovulation. The page marks these as the most fertile days within the window.
What if my cycle is irregular?
Enter your average cycle length. With irregular cycles the estimate is less reliable, and ovulation tests can help.
Can I use this to avoid pregnancy?
Calendar estimates are too uncertain to use as contraception. Your doctor can suggest methods that suit you.
What is the luteal phase?
The time from ovulation to your next period, usually 12 to 16 days. Leave it at 14 unless you know yours.