How to tell when you ovulate, and what each sign is worth

Ovulation is a single event that lasts less than a day, and almost every way of detecting it either tells you it is about to happen or tells you afterwards that it did. Knowing which is which matters enormously — for conceiving, for avoiding conception, and for making sense of your own cycle.

Cervical mucus: the earliest usable signal

As oestrogen rises through the follicular phase, cervical mucus changes in a predictable sequence. It goes from absent or sticky, to creamy and lotion-like, to clear, slippery and stretchy — the texture usually described as raw egg white. That fertile-quality mucus is what allows sperm to survive and travel; without it, sperm survive a matter of hours rather than days.

Peak mucus typically occurs in the day or two before ovulation. This makes it the most useful sign, because it is prospective: it tells you the fertile window is open now, not that it closed yesterday.

It is also free, and it is the sign most people have never been taught to look for.

Basal body temperature: accurate, but retrospective

Progesterone raises core temperature after ovulation. Taken at the same time each morning before getting up, temperature shows a sustained rise of roughly 0.3°C that persists until the period.

The shift is real and it is a good confirmation that ovulation occurred. But it happens after the egg is released, so by the time you see it on a chart, the fertile window has essentially closed. For conception timing, temperature tells you about the cycle you just had — useful over months, useless for this week.

It is also easily disrupted. A bad night's sleep, alcohol, illness, a warm room and an inconsistent wake time all move the number around enough to obscure the signal. Wearables that measure skin or wrist temperature overnight sidestep some of that, and they are genuinely better at picking up the shift than a thermometer used inconsistently.

LH tests: good, with a specific blind spot

Urine tests detect the luteinising hormone surge that triggers ovulation, generally 24 to 36 hours beforehand. That is prospective and precise, which is why they are the standard recommendation for people trying to conceive.

The blind spot: LH surges do not always result in ovulation, and some people — notably many with PCOS — have chronically elevated LH that produces persistent positives. A positive test means a surge happened. It does not guarantee an egg was released. If your tests are always positive, or never positive, that is worth mentioning to a doctor rather than buying a different brand. PCOS beyond the ovaries explains why the readings behave that way.

Mittelschmerz and libido: real, but not reliable enough to plan on

Roughly a fifth of people notice a one-sided lower abdominal ache around ovulation. It is thought to come from the follicle rupturing and the small amount of fluid or blood it releases irritating the peritoneum. When it is consistent and one-sided it is a decent personal marker. It is not consistent for most people.

Libido tends to rise in the days before ovulation. It is a genuine population-level pattern. It is also strongly affected by sleep, stress, relationship context and hormonal contraception, which makes it far too noisy to time anything by. Desire is responsive as often as it is spontaneous is the fuller picture.

What apps can and cannot know

This is the part worth being clear about. A tracking app that only knows your period dates is doing arithmetic on your past cycles. It is not detecting ovulation. It is predicting, from an average, when ovulation usually happens for someone with your recent cycle lengths.

That prediction is reasonable when cycles are consistent and near-worthless when they are not — and the months when your cycle is unusual are exactly the months the prediction is most wrong. Since it is the follicular phase that stretches, a stressful month moves ovulation but the app is still pointing at day 14. Why your cycle length changes explains the mechanism.

Apps that take in observed signals — temperature from a wearable, logged mucus, LH results — are doing something different and much better. They are recording an event rather than guessing at one.

The combination that actually works

For most purposes: cervical mucus to open the window, LH tests to narrow it, temperature to confirm afterwards. Mucus tells you to pay attention, LH tells you the specific days, temperature tells you at the end of the cycle whether the whole thing worked as expected.

For conception, the practical target is intercourse in the few days before ovulation rather than on the day itself, because sperm survive in fertile mucus for up to about five days while the egg is viable for less than one. The fertile window is shorter than most people think covers the arithmetic.

Why any of this matters if you are not trying to conceive

Ovulation is not only a fertility event. It is the thing that produces progesterone, and progesterone is what shapes the second half of your cycle — your sleep, your temperature, your mood, your digestion. A cycle without ovulation is a cycle without a luteal phase, and it feels different.

Knowing whether and roughly when you ovulate turns a period from an isolated event into an anchor point you can hang everything else on. It is what makes it possible to say "this happens on day 22" rather than "this happens sometimes".

Naked records these signals alongside your mood, sleep and everything else in your life, and looks for the connections between them — so the answer to "why do I feel like this" stops being a guess about averages and starts being an observation about you.