Ovulation tests. Cycle apps. Cervical mucus. Basal body temperature. Fertile windows.
Trying to conceive can start with “let’s see what happens” and somehow end with you examining toilet paper like a forensic scientist and knowing considerably more about luteinising hormone than you ever expected.
But underneath all the tracking, testing and notifications telling you that TODAY IS YOUR DAY, the basic biology is relatively straightforward.
Pregnancy is possible when sperm and an egg meet at the right time. Ovulation is the release of an egg from an ovary, while your fertile window describes the days during your menstrual cycle when sex can potentially result in pregnancy.[1][2]
The slightly inconvenient part?
Your body doesn't necessarily consult your app before ovulating.
So let's look at how ovulation works, when the fertile window actually occurs and what ovulation tests, cervical mucus and cycle tracking can, and cannot, tell you.
What is ovulation?
Ovulation happens when a mature egg is released from an ovary.
After its release, the egg enters the fallopian tube, where fertilisation may occur if sperm are present.[1]
Ovulation is part of the menstrual cycle, but it doesn't necessarily happen on the same calendar day for everybody or even on exactly the same day in every cycle.
Hormones coordinate the process.
During the first part of the menstrual cycle, follicles in the ovaries develop. One typically becomes dominant and contains the egg that will be released.
As ovulation approaches, levels of luteinising hormone (LH) rise sharply. This is known as the LH surge, and it helps trigger ovulation.
After ovulation, the empty follicle develops into a structure called the corpus luteum, which produces progesterone during the second half of the menstrual cycle.
Very efficient.
Also considerably more complicated than the flower icon on your period app would suggest.
When does ovulation happen?
You may have heard that ovulation happens on day 14.
Sometimes it does.
But day 14 is not a universal appointment your ovaries have collectively agreed to keep.
The idea comes from the textbook example of a 28-day menstrual cycle, where ovulation is often estimated to occur around the middle of the cycle.
Real menstrual cycles vary.
The NHS notes that ovulation usually occurs around 10 to 16 days before the start of the next period.[1]
That means somebody with a longer or shorter cycle may ovulate at a different point from somebody with a 28-day cycle.
And even if your periods are fairly regular, the exact day can vary from one cycle to another.
Stress, illness and other factors may also affect cycle timing.
So:
28-day cycle ≠ guaranteed day-14 ovulation.
Your ovaries did not sign the terms and conditions.
What is the fertile window?
The fertile window is broader than the day of ovulation itself.
This is because sperm and eggs have very different attitudes towards waiting around.
After ovulation, an egg remains capable of being fertilised for a relatively short period, generally around 12 to 24 hours.[2]
Sperm, meanwhile, can survive for several days within the female reproductive tract under suitable conditions. Research commonly describes a fertile window of approximately six days ending on the day of ovulation, although the probability of conception varies considerably across those days.[2][3]
This means sex does not need to happen at the precise moment an egg leaves the ovary.
Sperm can already be present when ovulation occurs.
Rather considerate of them, really.
When are you most likely to get pregnant?
The probability of conception isn't equal on every day of the fertile window.
Research suggests that the days immediately before ovulation are particularly important for conception.[2][3]
This makes biological sense.
If sperm are already present in the reproductive tract when the egg is released, fertilisation can potentially occur during the relatively short time the egg remains viable.
It also means that waiting until an app declares OVULATION DAY isn't necessarily the best way to think about timing.
By the time ovulation has definitely occurred, part of the fertile opportunity may already have passed.
How can you tell when you're ovulating?
This is where things become slightly more detective-like.
There are several ways people try to estimate or identify ovulation, including:
- menstrual cycle tracking
- ovulation predictor kits
- observing cervical mucus
- measuring basal body temperature
- combinations of several methods.
Each provides different information.
And none gives you a magical live feed from your ovary.
Can a period app predict ovulation?
Period and fertility apps can be useful for recording cycle dates and identifying patterns.
If your cycles are regular, an app can use previous cycle lengths to estimate when ovulation might occur.
The important word is estimate.
Research comparing app and calendar-based predictions with actual ovulation has found that methods relying only on cycle length cannot accurately predict the exact day of ovulation.[4]
Why?
Because the timing of ovulation can vary even when someone's cycle appears regular.
An app generally knows when you told it your previous periods started.
It doesn't necessarily know what your ovaries are doing today.
That doesn't make cycle apps useless. They're excellent for keeping records and noticing patterns.
Just don't mistake an algorithmic prediction for biological confirmation.
What do ovulation tests actually measure?
Ovulation predictor kits, sometimes called OPKs, usually test urine for luteinising hormone.
Remember that LH surge we mentioned earlier?
Ovulation tests are looking for it.
A positive result suggests that the LH surge has been detected and that ovulation is likely approaching. Ovulation commonly follows an LH surge within roughly the next day or so.
This can make OPKs more individualised than simply counting calendar days.
But there are limitations.
An LH surge indicates that your body is preparing to ovulate. It doesn't directly show an egg being released.
Some people may also experience more than one LH surge or have hormonal patterns that make tests more difficult to interpret.
So a positive ovulation test means something closer to:
“Your hormone pattern suggests ovulation may be approaching.”
Not:
“EGG RELEASE CONFIRMED. YOU HAVE 17 MINUTES.”
Thankfully.
What does cervical mucus tell you?
Yes, we're talking discharge.
We're all adults here.
Cervical mucus changes during the menstrual cycle in response to hormones. Around the fertile window, it often becomes wetter, clearer, more slippery and more stretchy.[5]
You may have heard this described as resembling raw egg white.
This type of mucus creates a more sperm-friendly environment and can therefore be a useful biological sign that fertility is increasing.
Unlike a calendar prediction, cervical mucus gives you information about what your body is doing during that particular cycle.
However, interpreting cervical mucus takes practice, and factors including infections, sexual activity, lubricants and some medicines can make observations more difficult.
If you notice discharge accompanied by symptoms such as an unusual smell, itching, pain or irritation, don't assume it's simply an ovulation sign. Speak to a healthcare professional if you're concerned.
What about basal body temperature?
Basal body temperature (BBT) is your resting body temperature measured under consistent conditions, usually immediately after waking.
After ovulation, progesterone causes a small increase in basal body temperature.
Tracking BBT over time can therefore help identify a temperature shift consistent with ovulation having occurred.
But there is a catch.
The temperature rise generally happens after ovulation.
So BBT is often better at helping you recognise that ovulation has probably already happened than predicting exactly when it is about to occur.
It can be useful for understanding patterns across several cycles, but it is less useful if your sole objective is receiving a flashing neon sign saying:
HAVE SEX TODAY.
Sleep disruption, illness, alcohol, travel and inconsistent measurement times can also affect temperature readings.
Bodies remain inconveniently committed to nuance.
Is combining methods more useful?
Potentially.
Because different fertility-awareness methods tell you different things, some people find combining them more informative.
For example:
Cycle tracking can provide a rough estimate based on previous patterns.
Cervical mucus can indicate that hormonal changes associated with the fertile phase are happening.
Ovulation tests can detect the LH surge that typically precedes ovulation.
Basal body temperature can provide retrospective evidence that ovulation may have occurred.
Together, these can give a fuller picture than relying on one app prediction.
That doesn't mean you need to use all of them.
Trying to conceive is allowed to involve sex without first completing a four-part data collection protocol.
How often should you have sex when trying to conceive?
If tracking ovulation makes you feel empowered and informed, excellent.
If it makes sex feel like a scheduled performance review, there is another option.
The NHS advises having sex every 2 to 3 days without contraception when trying to become pregnant.[6]
This approach means sperm are likely to be present around the fertile period without requiring you to identify the exact day of ovulation.
For some couples, targeted timing around the fertile window feels useful.
For others, regular sex without intensive tracking is considerably less stressful.
Neither approach earns you extra fertility points.
What if your cycles are irregular?
Predicting ovulation can be more difficult if menstrual cycles vary substantially in length or periods are infrequent.
Irregular periods don't necessarily mean that you aren't ovulating, but they can make calendar-based fertile-window predictions much less reliable.
Sometimes irregular or absent periods can also be associated with underlying conditions affecting ovulation.
If your periods are consistently very irregular, frequently absent or have changed significantly, speak to a healthcare professional, particularly if you're trying to conceive.
Tracking six different fertility metrics cannot compensate for a medical issue that deserves proper assessment.
Does tracking improve your chances of pregnancy?
Identifying the fertile window can help you time sex around the days when conception is biologically possible.
But there is an important emotional side to fertility tracking that rarely fits neatly into an app.
For some people, having more information reduces uncertainty.
For others, tracking every temperature, symptom, LH strip and bodily fluid becomes stressful.
You do not have to earn a pregnancy by becoming exceptionally good at fertility tracking.
An app notification isn't an instruction.
Missing one predicted fertile day doesn't mean you've “failed” that cycle.
And having sex precisely when an algorithm tells you to doesn't guarantee pregnancy.
Biology remains stubbornly uninterested in our spreadsheets.
Natural remedies, supplements and trying to conceive
Once you start searching for information about ovulation, you will probably also encounter plenty of advice about supplements, herbs, special diets and natural remedies for fertility.
Some nutrients have established roles before pregnancy. Folic acid, for example, is recommended before conception and during early pregnancy to reduce the risk of neural tube defects.[7]
But that is different from claiming that a particular herb, supplement or tea increases fertility.
If you're curious about raspberry leaf, nettle, chasteberry, maca, ashwagandha and other botanicals commonly associated with conception, our guide to Natural Remedies for Fertility: What Does the Science Actually Say? looks at the evidence without turning preliminary research into pregnancy promises.
Because “natural” and “proven to increase fertility” are not synonyms.
When should you get help when trying to conceive?
Not becoming pregnant immediately doesn't necessarily mean something is wrong.
The NHS notes that if you're under 40 and have regular sex without contraception, around 8 in 10 people will become pregnant within one year.[6]
The World Health Organization defines infertility as failure to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse.[8]
However, you don't necessarily need to wait 12 months before asking for advice.
Depending on your age, medical history, menstrual cycle, previous reproductive-health conditions or other circumstances, earlier assessment may be appropriate.
If you have irregular or absent periods, known conditions that could affect fertility or other concerns about your reproductive health, speak to a healthcare professional.
And fertility is not solely a female issue. Fertility difficulties can involve the male reproductive system, female reproductive system, both or remain unexplained.[8]
So no, responsibility for conception does not automatically belong to the person downloading the period app.
The bottom line
When you're trying to conceive, understanding ovulation can help make sense of when pregnancy is biologically possible.
Ovulation is the release of an egg from the ovary. The fertile window includes the days leading up to ovulation because sperm can survive in the reproductive tract for several days, while the egg remains available for fertilisation for a much shorter period.
Cycle apps can estimate fertile days but cannot reliably identify the exact day of ovulation from cycle length alone.
Ovulation tests detect the LH surge that typically happens before ovulation.
Cervical mucus can provide a real-time sign of increasing fertility.
Basal body temperature can help indicate afterwards that ovulation may have occurred.
You can use one method, combine several or decide that analysing your cervical mucus before breakfast isn't the lifestyle for you.
Regular sex every two to three days is also recommended when trying to conceive and can cover the fertile period without identifying ovulation precisely.
Because trying for a baby already comes with enough uncertainty.
Your ovaries don't need a project-management dashboard too.
References
[1] NHS. Periods and fertility in the menstrual cycle. Information on ovulation, menstrual-cycle timing and the fertile period.
NHS: Periods and fertility
[2] Wilcox AJ, Weinberg CR, Baird DD. (1995). Timing of sexual intercourse in relation to ovulation: effects on the probability of conception, survival of the pregnancy, and sex of the baby. New England Journal of Medicine, 333, 1517–1521.
PubMed: Timing of intercourse and ovulation
[3] Dunson DB, Baird DD, Wilcox AJ, Weinberg CR. (1999). Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation. Human Reproduction, 14(7), 1835–1839.
PubMed: Day-specific probability of pregnancy
[4] Johnson S, Marriott L, Zinaman M. (2018). Can apps and calendar methods predict ovulation with accuracy? Current Medical Research and Opinion, 34(9), 1587–1594.
PubMed: Accuracy of ovulation prediction methods
[5] American College of Obstetricians and Gynecologists (ACOG). Fertility Awareness-Based Methods of Family Planning. Information on cervical mucus, basal body temperature and fertility awareness.
ACOG: Fertility awareness-based methods
[6] NHS. Trying to get pregnant. NHS advice on timing sex, conception and when to seek medical advice.
NHS: Trying to get pregnant
[7] NHS. Vitamins, supplements and nutrition in pregnancy. Guidance on folic acid before conception and during early pregnancy.
NHS: Vitamins, supplements and nutrition
[8] World Health Organization (WHO). Infertility. Information on the definition, prevalence and causes of infertility.
WHO: Infertility
This article is for general information only and isn't intended to diagnose fertility problems or replace individual medical advice. If you have concerns about ovulation, your menstrual cycle or your fertility, speak to an appropriately qualified healthcare professional.
