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Ovulation Calculator

Find your estimated ovulation day, fertile window and best days to conceive, shown on a calendar for the next three cycles. Everything is calculated in your browser, and nothing is uploaded.

Count from day 1 of one period to day 1 of the next.
Ovulation to next period. Most people are 12 to 14.
My cycles are not always the same length
This is an estimate from your cycle length, not a measurement of your hormones. Ovulation can shift from cycle to cycle, especially with stress, illness, travel or irregular periods. For more precision, you can use ovulation test strips, track your basal body temperature, or watch cervical mucus. Sperm can survive for up to 5 days, which is why the fertile window starts before ovulation. This tool is not a reliable method of contraception, and it is not medical advice. If you have been trying to conceive for 12 months (6 months if you are over 35) without success, or your cycles are very irregular, talk to a healthcare provider.

About this tool

Ovulation Calculator estimates your fertile window, the days in your cycle when pregnancy is most likely, based on the start date and length of your cycle. People who are trying to conceive often use it to plan.

It is an estimate. Ovulation can shift from cycle to cycle, so the dates are a guide and not a guarantee.

How to use it

  1. Enter the first day of your last period.
  2. Enter the usual length of your cycle in days.
  3. Press calculate.
  4. Read your estimated ovulation date and fertile window.

Example

With a 28-day cycle that began on the 1st, ovulation is usually estimated around day 14, so the fertile window is the few days leading up to and including that date. If your cycle is longer or shorter, the dates move accordingly.

Tips

  • The more regular your cycles, the more reliable the estimate.
  • Combine the calendar estimate with other signs if you are tracking carefully, and speak to a health professional for personal advice.
  • If you have been trying to conceive for a while without success, a doctor can offer support and tests.

Questions people ask

How accurate is it?

It is an estimate based on an average pattern. Your own ovulation may happen earlier or later.

Can I use it as contraception?

No. It is not reliable for preventing pregnancy.

Does it work with irregular cycles?

Less well. If your cycles vary a lot, the estimate will be less dependable.

Is my information stored?

The calculation uses only the details you enter on the page.

For general information only. It is not medical advice, not a diagnostic tool and not a method of contraception. Speak to a doctor about your own health and fertility.