Everything You Need to Know About Ovulation

Ovulation is the release of a mature egg from one of your ovaries, triggered by a surge in luteinising hormone (LH). It happens once per menstrual cycle and marks the point when pregnancy is biologically possible, but it is also an indicator that your hormones are working as they should, whether or not you are trying to conceive.

This guide covers everything you need to know: how ovulation happens, when it happens, what it means for your health, the myths that routinely mislead people, what the physical signs look like, and what can disrupt the process.

Quick facts

• Ovulation is when a mature egg is released from one of your ovaries each month
• Your fertile window is the five days before ovulation and the day of ovulation itself, and is when chances of pregnancy are the highest.
• The egg survives for 12–24 hours after release, but sperm can survive up to five days in the female reproductive tract.
• Ovulation timing depends on your cycle length, it is not always on day 14 of your cycle
• Ovulation can be disrupted by stress, weight changes, PCOS, and other hormonal conditions

How does ovulation work?

Ovulation is the result of a hormonal sequence that begins the moment your period starts, not something that happens in isolation mid-cycle.

At the start of each menstrual cycle, the hypothalamus, a small region at the base of your brain releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland (also in the brain), to make follicle-stimulating hormone (FSH). FSH stimulates a group of follicles in the ovaries to begin developing, each one containing an immature egg. 

Several follicles begin growing simultaneously, but over the following one to two weeks, one becomes dominant – larger and more developed than the rest (which are gradually reabsorbed by the body).

As the dominant follicle grows, it produces rising levels of oestrogen. This oestrogen has two simultaneous effects: it thickens the lining of the uterus in preparation for a potential pregnancy, and it sends a hormonal signal back to the pituitary gland. When oestrogen reaches a peak, it triggers dramatic release of luteinising hormone – the LH surge. This surge is the direct trigger for ovulation. Within 24 to 36 hours, the dominant follicle ruptures and releases its mature egg into the fallopian tube to be fertilised.

What happens next matters as much as the egg release itself. After the egg is released, the empty follicle transforms into a structure called the corpus luteum, which makes progesterone for the remainder of the cycle. Progesterone stabilises the uterine lining and supports implantation. If fertilisation does not occur, the corpus luteum breaks down, progesterone falls, and your period begins, resetting the cycle.

This is also why ovulation matters beyond reproduction. The progesterone produced after ovulation can also support things like mood regulation and sleep quality (ref), which is why anovulatory cycles can affect how you feel well beyond any question of fertility.

When does ovulation happen in your cycle?

Ovulation itself is a single event, not a process. The moment the dominant follicle ruptures and releases the egg is ovulation and the egg’s viability window is just 12 to 24 hours from that point. After that, if unfertilised, it breaks down.

So, does ovulation always happen on day 14? Only in the context of a textbook 28-day cycle, and even then, it’s an approximation. In reality, ovulation occurs around 12 to 16 days before your next period, not 14 days after your last one. That distinction matters, because it means ovulation timing shifts depending on your cycle length.

For example, in a shorter 24-day cycle, ovulation may occur as early as days 8 to 12. In a longer 35-day cycle, it may not happen until days 19 to 23. While day 14 is often quoted as the “average”, applying it as a universal rule is misleading. Cycle lengths vary widely between individuals and even from month to month in the same person.

Research has found that in only around 30% of women does the fertile window fall within the days identified by clinical guidelines (days 10 to 17). For the majority, the fertile window occurs either earlier or later than this range.

If you are taking birth control or hormonal contraception, you will not ovulate. These methods work primarily by suppressing ovulation and also thickening cervical mucus, making it harder for sperm to reach and fertilise an egg.

It’s also important to understand where cycle variability comes from. The second half of the cycle, from ovulation to your next period (the luteal phase) tends to be relatively consistent, typically lasting around 14 days. The variation in total cycle length mostly comes from the first half (the follicular phase), which is why ovulation timing can shift.

Even if you have regular cycles, ovulation isn’t perfectly predictable. Factors like stress, illness, travel, weight fluctuation, and disrupted sleep can delay ovulation by interfering with the hormonal signals that trigger it. When a period arrives later than expected, it’s usually because ovulation happened later,  not because the period itself was delayed.

What is the fertile window?

Your fertile window is a six-day window during each menstrual cycle, the five days leading up to ovulation and the day of ovulation itself when you are most likely to get pregnant.

An egg can only survive for 12–24 hours after ovulation, but sperm can survive for up to five days in the female reproductive tract, so if you have unprotected sex in the days before ovulation, pregnancy is still possible. Recent research has shown that the two to three days immediately before ovulation carry the highest probability of conception.

In 2025, Hertility’s research team published a peer-reviewed study in Reproductive Health that has become the largest of its kind on fertility awareness in women actively trying to conceive.

Analysing responses from 97,414 women, the study found that more than 41% could not accurately identify their fertile window.  Women with irregular cycles, younger women and those who had been trying to conceive for longer were all significantly less likely to identify the fertile window correctly. Misunderstanding about their own cycle regularity compounded the problem: women who incorrectly believed their cycles were regular when they were not were nearly three times more likely not to know their fertile window.

What are the signs of ovulation?

Your body produces a recognisable set of physical signs and symptoms  around ovulation. Not everyone experiences all of them, but knowing what to look for is the first step in understanding your cycle.

The most consistent physical sign is a change in cervical mucus. In the days before ovulation, discharge becomes increasingly clear, slippery, and stretchy, a consistency often compared to raw egg white. This mucus coincides with peak fertility and is driven by rising oestrogen. After ovulation, progesterone causes mucus to thicken and reduce.

Other signs include a mild one-sided ache or twinge in the lower abdomen (mittelschmerz), a slight rise in basal body temperature (BBT) after ovulation has occurred, light mid-cycle spotting, increased libido, and breast tenderness.

To know more about the signs of ovulation, read our blog here.

How can you track ovulation signs and symptoms?

There are several methods you can use to track ovulation, including ovulation test kits, monitoring cervical mucus changes, tracking basal body temperature, and using a period tracking app. Each has different strengths and limitations.

Ovulation predictor kits (OPKs)

Ovulation predictor kits detect the LH surge in your urine (the hormonal spike that occurs 24 to 36 hours before ovulation). They work similarly to a pregnancy test and are considered the most reliable at-home method for identifying your fertile window in advance. A positive OPK result means ovulation is likely within the next day to day and a half.

OPKs may not be suitable for people with PCOS, because they often have high LH levels which might trigger a  false positive result across multiple days rather than indicating a genuine imminent surge. 

Hormone blood testing 

If you are trying to get pregnant and are concerned about whether you are ovulating, a day 21 (mid-luteal) progesterone is the most direct clinical way to confirm ovulation has occurred.  

A comprehensive hormone panel including FSH, LH, oestradiol, AMH, prolactin, TSH, and androgens helps assess the hormonal pathways that regulate ovulation. Rather than confirming ovulation directly, these markers provide insight into whether your hormones are supporting regular ovulation, and can help identify reasons why ovulation may be irregular or absent.

Hertility’s Advanced At-Home Hormone and Fertility Test measures this full panel, giving you a clear, clinically informed picture of your reproductive hormone health and helping you understand whether your body is set up to ovulate regularly.

Calendar tracking

Calendar tracking is often a good starting point. This involves recording the first day of your period each month to work out your cycle length over time. You can do this using a calendar, diary, or a period tracking app. Many people also track symptoms like mood changes, cervical mucus, or cramps to start identifying patterns across their cycle.

Period tracking apps use this data to estimate your fertile window, typically based on past cycle lengths. But these predictions are just that, estimates. The apps are reliant on the accuracy of what you enter and most do not account for cycle-to-cycle variation or external factors like stress or illness. This means they can sometimes miscalculate your fertile window, especially if your cycles are irregular. This means you could be mistiming sex when trying to conceive or have a false sense of “safe days,” increasing the risk of unintended pregnancy

Cervical mucus changes

Cervical mucus changes throughout your menstrual cycle in response to shifting hormone levels and plays a key role in conception. Before ovulation it is typically thick, sticky, and creamy.  As oestrogen rises in the lead-up to ovulation, it becomes clear, slippery and stretchy resembling raw egg whites. This consistency makes it easier for sperm to swim up the vagina and into the uterus to meet and fertilise an egg.

After ovulation, progesterone causes mucus to thicken and reduce again.

Cervical mucus can be affected by many other factors, such as infections, medications, lubricants, and arousal, so it should be used alongside other methods rather than alone.

Basal body temperature (BBT) changes

After ovulation, the rise in progesterone causes a small but measurable increase in your resting body temperature, typically 0.5°C to 1 which remains elevated for the rest of your cycle.

To use this method effectively, take your temperature at the same time every morning before getting out of bed, eating, or drinking, using a dedicated basal body thermometer. After two to three cycles of consistent tracking, you should be able to identify your typical post-ovulation temperature pattern.

The key limitation: BBT confirms ovulation has already occurred, it cannot predict it in advance. By the time you see the temperature rise, the egg has already been released. BBT is most useful for understanding your cycle pattern over time rather than timing conception in a given month.

Basal body temperature can also be disrupted by alcohol, illness, disturbed sleep, and changes in routine, so look for a sustained rise of at least three consecutive days rather than a single elevated reading.

Physical ovulation symptoms

Some people notice physical signs around ovulation, including breast tenderness, an increased sex drive, mild pelvic or abdominal pain (mittelschmerz), light spotting, bloating, heightened senses, mood changes, and appetite changes.

These symptoms are genuine physiological responses to the hormonal shifts occurring around ovulation, but they are too inconsistent to rely on as a standalone method for predicting your fertile window. 

To know more about the how to track ovulation, read our blog here

What can cause ovulation to stop?

When a cycle occurs without the release of an egg, it’s called anovulation. It’s more common than many people realise and importantly, it doesn’t always mean your periods stop altogether. You can still experience bleeding that looks like a period during an anovulatory cycle, even though ovulation hasn’t occurred.

There are several underlying causes of anovulation, most of which relate to disruptions in the hormonal signals that regulate the menstrual cycle.

PCOS (polycystic ovary syndrome) is the most common cause. It affects how the ovaries develop and release eggs, often due to hormonal imbalances, particularly involving androgens and insulin.

Thyroid dysfunction — both underactive (hypothyroidism) and overactive (hyperthyroidism) can interfere with ovulation, making cycles irregular or preventing ovulation altogether.

Elevated prolactin levels can also suppress ovulation. Prolactin is the hormone responsible for milk production, and when levels are high outside of pregnancy or breastfeeding, it can disrupt the signals needed for ovulation.

Primary ovarian insufficiency (POI) is a less common but important cause. It occurs when the ovaries stop functioning as expected before the age of 40, leading to reduced or absent ovulation.

There are also physiological and lifestyle-related factors that can temporarily affect ovulation. Similarly, approaching menopause can lead to more frequent anovulatory cycles as hormone levels fluctuate.

External factors such as chronic stress, fatigue, significant or rapid weight changes, and excessive exercise can also disrupt the hormonal cascade required for ovulation, sometimes leading to skipped or irregular ovulation even in otherwise healthy individuals.

Understanding that bleeding doesn’t always equal ovulation is key and if anovulation is happening frequently, it’s worth investigating further to identify the underlying cause.

Frequently asked questions about ovulation

What is ovulation?

Ovulation is the release of a mature egg from one of your ovaries, triggered by a surge in luteinising hormone (LH). It occurs once per menstrual cycle and is the only point during which natural conception is possible. It is also a key indicator of hormonal health, independent of whether you are trying to conceive.

When does ovulation occur in your cycle?

Ovulation occurs 12 to 16 days before your next period begins. On a 28-day cycle this typically falls around day 14, but on a 35-day cycle it may not happen until day 19 to 23. The timing depends entirely on your individual cycle length and can shift from month to month.

Is ovulation always on day 14?

No. Day 14 only applies to a 28-day cycle. Because ovulation occurs 12 to 16 days before your next period, not 14 days after your last one, the date shifts completely with your cycle length. Assuming day 14 when your cycle is longer or shorter will mismatch your actual fertile window.

Can you have a period without ovulating?

Yes. Anovulatory bleeding can occur when oestrogen rises and falls without the progesterone-driven luteal phase that follows true ovulation. This bleeding can resemble a period in timing and appearance but has not been preceded by egg release. While regular cycles are generally a good sign that ovulation is happening, it is not a confirmation.

Does ovulation mean you are fertile?

Ovulation is necessary for natural conception but doesn’t guarantee it. This is because there are many other factors that influence fertility including the health of the Fallopian tubes, the uterus and even sperm health. 

Is ovulation the same as the fertile window?

No. Ovulation is the event, the moment the egg is released. The fertile window is the period of time around that event when conception is possible. You can be within your fertile window before ovulation has happened.

Resources:

• https://www.thewomens.org.au/health-information/fertility-information/getting-pregnant/ovulation-and-conception#:~:text=Once%20inside%20the%20walls%20of,absorbed%20back%20into%20the%20body
• https://my.clevelandclinic.org/health/articles/23439-ovulation 
• https://www.ncbi.nlm.nih.gov/books/NBK549822/
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7721003/#:~:text=When%20a%20woman%20is%20younger,on%20the%20ovary%20and%20eggs.
• https://www.tommys.org/pregnancy-information/planning-a-pregnancy/fertility-and-causes-of-infertility/how-age-affects-fertility
• https://www.ncbi.nlm.nih.gov/books/NBK441996/
• https://www.tommys.org/pregnancy-information/planning-a-pregnancy/how-to-get-pregnant/ovulation-and-fertility
• https://www.nhs.uk/common-health-questions/sexual-health/how-can-i-tell-when-i-am-ovulating/ 
• https://www.parents.com/getting-pregnant/ovulation/fertile-days/ovulation-pros-and-cons-of-ovulation-predictor-kits-opks/