Cervical Mucus Calculator

If you're trying for a baby, knowing when you ovulate can help you understand when you're most likely to conceive. Your body gives several clues, and one of the most useful is the change in your cervical mucus through the month.

This guide explains how ovulation fits into your cycle, how long you're fertile for, and how to read the signs. To estimate your dates, use the ovulation calculator.

What is ovulation?

Ovulation is when one of your ovaries releases an egg. It happens once in each menstrual cycle. After it's released, the egg travels along the fallopian tube, where it can be fertilised by sperm.

The egg only survives for about 12 to 24 hours, but sperm can live inside the body for several days. That's why the days before ovulation matter as much as the day itself.

When does ovulation happen?

The second half of the cycle, from ovulation to your next period, is called the luteal phase. It's fairly consistent, usually lasting about 14 days. The first half varies much more from person to person.

So ovulation usually happens about 14 days before your next period starts, not 14 days after your last one. In a 28-day cycle that's around day 14. In a 32-day cycle it's around day 18, and in a 24-day cycle around day 10.

The ovulation calculator uses your usual cycle length to count back from your next expected period.

Your fertile window

Because sperm can survive for several days and the egg for up to a day, your most fertile time is about six days long: the five days before ovulation and the day of ovulation itself. Having sex during this window, and particularly in the two or three days before ovulation, gives the best chance of conceiving.

The NHS advises that having sex every two to three days throughout your cycle is a good way to make sure there's sperm present when you ovulate, without needing to pinpoint the exact day.

How cervical mucus changes through your cycle

Cervical mucus is fluid produced by the cervix. Its texture and amount change in response to hormones, and many people use these changes to recognise when they're approaching ovulation.

The clear, stretchy "egg white" mucus is a sign you're at your most fertile. It helps sperm travel and survive. The last day you notice this type of mucus is often close to ovulation.

How to check

You can notice mucus on toilet paper, underwear or by gently checking with clean fingers. Noting what you see each day for a few cycles helps you spot your own pattern. Things like infections, some medicines and breastfeeding can affect mucus, so it isn't reliable for everyone.

Other signs of ovulation

• Ovulation predictor kits detect the surge in luteinising hormone (LH) that happens about a day before ovulation.
• Basal body temperature rises slightly after ovulation. Tracking it confirms ovulation has happened, though it can't predict it in advance.
• Mild pain on one side of the lower abdomen, sometimes called mittelschmerz, affects some people around ovulation.
• Changes in the cervix, which may feel softer and higher around ovulation.

Using more than one sign together gives a clearer picture than any one alone.

Irregular cycles

If your cycles vary a lot in length, predicting ovulation from dates alone is harder. In that case, tracking cervical mucus or using ovulation tests can be more helpful than a calendar. Very irregular or absent periods can sometimes be a sign of a condition such as polycystic ovary syndrome, so it's worth speaking to a GP.

When to get advice

Most couples conceive within a year of trying. The NHS recommends seeing a GP if you haven't conceived after a year of regular unprotected sex, or sooner if you're 36 or over or know of a possible fertility problem. You should also see a GP if you have very irregular periods, no periods, or pain during sex.

Lifestyle and fertility

General health can affect fertility for both partners. The NHS suggests that people trying for a baby stop smoking, keep alcohol within low-risk limits or avoid it, aim for a healthy weight and take a daily folic acid supplement from before conception until 12 weeks of pregnancy. Stress and long working hours don't necessarily stop you conceiving, but looking after your wellbeing can make trying for a baby easier.