If you're trying for a baby, understanding your menstrual cycle can help you recognise when you're most likely to conceive.
Your chances of becoming pregnant are highest around the time of ovulation, when an egg is released from one of your ovaries. But ovulation doesn't necessarily happen on day 14 – and your most fertile days can vary from one cycle to the next.
Here's how your fertile window works and some of the signs that may help you recognise when you're ovulating.
When are you most fertile?
Ovulation happens when an egg is released from one of your ovaries. For many women, this happens around 10 to 16 days before the start of their next period, rather than on one particular day of the menstrual cycle.
Once released, an egg can only be fertilised for a relatively short time. Sperm, however, can survive inside the female reproductive tract for several days.
This means it's possible to become pregnant from sex in the days leading up to ovulation as well as around the time the egg is released.
If you're trying to conceive, having regular sex every two to three days throughout your cycle can help ensure you're having sex around your fertile window without needing to identify the exact day of ovulation.
How can you work out your fertile days?
There's no completely reliable way to predict exactly when you'll ovulate at home, particularly as menstrual cycles can vary.
However, tracking your cycle and paying attention to changes in your body can help you become more familiar with your own pattern.
1. Track your menstrual cycle
The first day of your period is day one of your menstrual cycle. Keeping a record of when your periods begin can help you understand how long your usual cycle lasts and whether it's fairly regular.
Ovulation generally happens around 10 to 16 days before your next period starts.
If your periods are regular, looking back over previous cycles may give you an idea of when you're likely to ovulate. However, calendar calculations are estimates and shouldn't be relied upon to identify the exact day of ovulation.
Period-tracking apps and online ovulation calculators can also provide estimates, but they can't tell you for certain when you have ovulated.
2. Look for changes in cervical mucus
Your vaginal discharge naturally changes throughout your menstrual cycle as hormone levels change.
Around the time of ovulation, cervical mucus typically becomes thinner, clearer and more stretchy. It's often compared to the consistency of raw egg white.
This type of cervical mucus helps sperm move through the cervix and can be one sign that you're approaching your most fertile time.
After ovulation, your discharge will usually change again. Getting to know what's normal for you can make these differences easier to recognise over time.
3. Track your basal body temperature
Your basal body temperature is your body's temperature when you're completely at rest. It's usually measured first thing in the morning, before you get out of bed.
After ovulation, hormonal changes cause a small increase in basal body temperature, which usually remains higher until your next period.
Recording your temperature over several cycles may help you identify a pattern and understand when ovulation is likely to have happened.
However, because the temperature increase happens after ovulation, basal body temperature isn't a reliable way to predict ovulation in advance when used on its own.
4. Consider an ovulation test
Ovulation predictor kits can provide another way of tracking your fertile window.
These tests detect a rise in luteinising hormone (LH) in your urine. LH levels rise shortly before ovulation, so a positive result can indicate that ovulation is approaching.
Ovulation tests can't guarantee that you'll become pregnant, but they can provide useful additional information when you're getting to know your cycle.
What if my periods are irregular?
Working out when you're likely to ovulate can be more difficult if your periods aren't regular.
Rather than trying to identify one particular fertile day, having sex regularly throughout your cycle can help increase the likelihood of having sex around the time of ovulation.
There are many reasons why periods can be irregular. If your cycles are irregular and you're concerned about your fertility or are finding it difficult to become pregnant, speak to your GP for advice.
Don't let tracking take over
When you're trying for a baby, it can be easy for dates, apps, temperatures and ovulation tests to become a big part of everyday life.
Understanding your cycle can be useful, but you don't necessarily need to pinpoint the exact moment you ovulate. Regular sex throughout your cycle can help cover your fertile window without everything having to revolve around one particular date.
And remember that becoming pregnant can take time. If you've been trying to conceive without success or you have concerns about your fertility, menstrual cycle or reproductive health, speak to your GP for individual advice.
FAQs about fertile days and ovulation
When are you most fertile?
You're most fertile around the time of ovulation. Ovulation generally happens around 10 to 16 days before your next period starts, although the exact timing can vary between women and from one cycle to another.
Is ovulation always on day 14?
No. Day 14 is commonly used as an example for a 28-day menstrual cycle, but cycles vary and ovulation doesn't always happen on day 14.
How many fertile days are there in a month?
Your fertile window includes the days leading up to ovulation and around the time the egg is released. Because sperm can survive inside the female reproductive tract for several days, sex before ovulation can result in pregnancy.
How can I tell when I'm ovulating?
Changes in cervical mucus can help you recognise when ovulation may be approaching, while a rise in basal body temperature can indicate that ovulation has already happened. Ovulation predictor kits can also detect the hormonal surge that usually occurs shortly before ovulation.
Can I get pregnant outside my predicted fertile days?
Yes. Ovulation can be difficult to predict precisely and the timing can change from one cycle to another. Predicted fertile days shouldn't therefore be considered a guarantee of when pregnancy can or cannot occur.
How often should you have sex when trying for a baby?
Having sex every two to three days throughout your cycle can help ensure you're having sex around the time of ovulation without needing to identify one particular fertile day.
This article provides general information and isn't a substitute for medical advice. If you have concerns about your fertility, menstrual cycle or reproductive health, speak to your GP or another healthcare professional.
