Ovulation: signs, timing and your fertile window

In short: ovulation is when one of your ovaries releases an egg. It usually happens about 12 to 14 days before your next period, around day 14 of a 28-day cycle. The egg lives for 12 to 24 hours, but sperm can survive up to five days, so your fertile window is about six days long: the five days before ovulation, plus ovulation day.

In Periodiva, this is your Shine phase.

What happens when you ovulate

Through the follicular phase, one follicle in your ovary ripens an egg and makes rising amounts of estrogen. When estrogen peaks, your brain releases a sudden surge of luteinising hormone (LH). That surge triggers the follicle to release its egg into the fallopian tube (Cleveland Clinic).

The empty follicle then becomes the corpus luteum, which makes progesterone for the luteal phase that follows.

When do you ovulate?

The textbook answer is day 14 of a 28-day cycle, but only some cycles follow the textbook. Cycles from 21 to 35 days are normal, and ovulation moves with them (Cleveland Clinic).

A more useful rule: ovulation usually comes 12 to 14 days before your next period, because the phase after ovulation is fairly steady (Cleveland Clinic). So in a 32-day cycle, it's more likely around day 18.

Even so, timing shifts. In a study of more than 600,000 cycles, the time from period to ovulation ranged from about 10 to 30 days (Bull et al., 2019).

Your fertile window

An egg survives about 12 to 24 hours after it's released, while sperm can live for three to five days (Cleveland Clinic). Together, that makes a fertile window of roughly six days.

A landmark study of 221 women found that pregnancy only began when sex happened during the six days ending on ovulation day. The chance of conceiving from sex on a single day rose from about 10% five days before ovulation to about 33% on ovulation day itself (Wilcox et al., 1995).

So the two days before ovulation, and ovulation day, are the most fertile.

Signs you're ovulating

Your body often gives clues (Cleveland Clinic):

• Cervical mucus becomes clear, slippery and stretchy, like raw egg white, in the days before ovulation.
• Basal body temperature, taken first thing in the morning before you get up, rises slightly after ovulation, by about 0.5 to 1 °F (roughly 0.3 to 0.6 °C). It confirms ovulation has happened rather than predicting it, so track it over a few months.
• Ovulation tests pick up the LH surge in your urine. A positive result usually means ovulation within about 36 hours.
• Ovulation pain: a one-sided twinge or cramp low in your tummy, sometimes called mittelschmerz.
• Other changes some people notice: tender breasts, bloating, light spotting, a higher sex drive, or a sharper sense of smell or taste.

Not everyone notices signs, and that's normal.

How you might feel

Around ovulation, estrogen is at its peak, and many people feel confident, social and energetic. It's a lovely time for big conversations, plans with friends, or a workout that asks a bit more of you, if you feel like it.

When to talk to a doctor

• Ovulation pain is severe, lasts more than a day or two, or comes with fever or heavy bleeding.
• Your cycles are very irregular, or you rarely notice any signs of ovulation over several months.
• You've been trying to get pregnant for a while without success.

Important: this isn't contraception

Because ovulation can move from cycle to cycle, counting days alone can't reliably prevent pregnancy. If you want to avoid pregnancy, talk to a doctor or nurse about contraception that suits you.

Estimate your fertile window

Our free ovulation calculator estimates your fertile window, most fertile days and ovulation for your next three cycles. It runs on your device and saves nothing.

Next: the luteal phase, and why PMS happens.