Ovulation Calculator

Estimate when you are most likely to ovulate and the days you are most fertile.

This tool gives general estimates only and is not medical advice. Always follow the guidance of your healthcare provider.

How ovulation is estimated

Ovulation usually happens about 14 days before the next period starts. So the estimated ovulation day is your cycle length minus your luteal phase (the days between ovulation and your next period). The fertile window runs from five days before ovulation through the day after, because sperm can survive for several days.

Ovulation tests, basal body temperature and cervical mucus can make this more precise than a calendar estimate.

The best days to try

You can only get pregnant on a handful of days each cycle. Sperm can survive in the body for up to about five days, while an egg lives for around a day after ovulation. A well-known study of couples trying to conceive found that the chance of pregnancy was highest from intercourse in the two days before ovulation and on the day of ovulation itself. That is why the fertile window shown here starts five days before your estimated ovulation day.

Signs that you are ovulating

Cervical mucus becomes clear, slippery and stretchy, a bit like raw egg white, in the days before ovulation.
Ovulation tests detect the rise in luteinizing hormone (LH) that comes a day or so before ovulation.
Basal body temperature rises slightly after ovulation. Tracking it confirms that ovulation happened, which helps you predict future cycles.
Some people notice a mild ache on one side of the lower abdomen.

How to find your cycle length

Count from the first day of one period (day 1) up to the day before your next period starts. Cycles between 21 and 35 days are common in adults. If yours vary, use your average from the last few months, and treat the result as a rough guide.

Frequently asked questions

Is this reliable if my cycles are irregular?

Not very. Calendar estimates work best with regular cycles. Ovulation test strips or tracking temperature give better information.

Can I use this for birth control?

No. This is not a contraceptive method and should not be used to avoid pregnancy.

When should I talk to a doctor?

Many doctors suggest checking in after 12 months of trying, or 6 months if you are over 35, or sooner if you have irregular cycles.

What is the luteal phase?

It is the part of your cycle after ovulation, ending when your next period starts. It is fairly steady for most people at around 12 to 14 days, which is why the calculator counts back from your next period.

Can I get pregnant outside the fertile window?

It is much less likely, but calendar estimates can be off by several days, especially if ovulation comes early or late in a particular cycle.