Progesterone

Progesterone at a glance

What is progesterone?

Progesterone is a hormone made mainly by your ovaries after you release an egg. It is often shortened to P4 on lab reports, which is simply its chemical shorthand. It is a steroid hormone, meaning it is built from cholesterol, and it belongs to the same family as Oestradiol (Oestrogen) and Testosterone (total). People often ask whether progesterone is a female hormone or a male hormone. The honest answer is that it is neither, exclusively. It is usually described as a female sex hormone because it does its most visible work in the menstrual cycle and in pregnancy, but men produce small amounts too, from the adrenal glands and testes.

Progesterone works in partnership with oestrogen rather than in competition with it. Oestrogen builds; progesterone settles. That relationship is the reason a progesterone result is difficult to interpret on its own, and why it is usually measured alongside other hormones.

Where is progesterone produced?

Progesterone comes from three places in the body, and a fourth during pregnancy.

Diagram showing where progesterone is produced in the body: the corpus luteum, ovaries, adrenal glands and placenta

The corpus luteum is the main source. When your ovary releases an egg, the empty follicle left behind doesn’t simply disappear. It reorganises itself into a temporary gland called the corpus luteum, and that structure produces the large surge of progesterone that defines the second half of your cycle. If no pregnancy occurs, the corpus luteum breaks down after around 10 to 14 days and progesterone falls away with it.

The ovaries produce small amounts across the cycle, in women who are still ovulating.

The adrenal glands, which sit just above each kidney, make a small background amount. This happens in everyone, including men, and it is the reason a progesterone result is never truly zero.

The placenta takes over production from around weeks 8 to 10 of pregnancy, and produces progesterone in far larger quantities than the corpus luteum ever did.

This matters for reading your own result. Before ovulation there is no corpus luteum, so your progesterone comes only from the adrenal glands and stays very low, that is by design, not a fault. The same applies after menopause: once the ovaries stop releasing eggs, no corpus luteum forms, production falls back to the small adrenal contribution, and levels stay low permanently.

What triggers progesterone production?

The trigger is a sharp rise in Luteinising Hormone (LH), often called the LH surge. LH climbs steeply around the middle of your cycle, causes the ovary to release an egg, and then prompts the leftover follicle to convert into the corpus luteum. Progesterone production follows from there.

So what regulates progesterone is really a chain: the brain releases LH, LH triggers ovulation, ovulation creates the corpus luteum, and the corpus luteum makes progesterone. Anything that interrupts that chain (significant stress, very low body weight, heavy training loads, thyroid problems, Polyendocrine Metabolic Ovarian Syndrome (PMOS), hormonal contraception, or approaching menopause) can affect how much progesterone you produce, because it affects whether and when you ovulate.

What does progesterone do?

Progesterone’s main job is preparation and maintenance. Oestrogen spends the first half of your cycle building up the lining of your womb; progesterone spends the second half making that lining stable, receptive and ready for a fertilised egg.

Beyond the womb, progesterone:

• Raises your basal body temperature by around 0.2 to 0.5°C after ovulation, which is why temperature tracking can indicate that ovulation has happened
• Has a calming, sedative effect on the brain, through a breakdown product called allopregnanolone that acts on the same receptors as anti-anxiety medication
• Supports breast tissue development in preparation for possible pregnancy
• Helps regulate fluid balance, acting as a mild natural diuretic
• Protects the womb lining from the thickening effect of unopposed oestrogen

Progesterone and the uterine lining

Progesterone is the hormone that maintains the uterus lining. Oestrogen grows the endometrium; progesterone then converts it from a growing tissue into a stable, secretory one that can support an embryo. It thickens and softens the lining, prompts the glands within it to secrete nutrients an early embryo can use, reduces contractions in the uterine muscle so the lining is not disturbed, and thickens cervical mucus. If a fertilised egg implants, progesterone keeps the lining in place. If it doesn’t, progesterone falls, the lining is shed, and your period begins.

Progesterone vs oestrogen: how they work together

The two hormones are best understood as a sequence rather than a pair of opposites.

Because they act in sequence, a progesterone result read on its own tells you less than a progesterone result read alongside Oestradiol, LH, and Follicle Stimulating Hormone (FSH). This is the reasoning behind hormone panels rather than single-marker tests.

How progesterone affects how you feel

Progesterone is one of the more noticeable hormones, and many of the things people attribute vaguely to “hormones” in the second half of the cycle are progesterone’s doing.

• Tiredness and sleepiness: progesterone is converted into allopregnanolone, which acts on the same receptors in the brain as sedative medication. This is why many women feel noticeably more tired in the luteal phase, and why progesterone taken as HRT is usually prescribed at bedtime.
• Bloating and weight: progesterone does not cause fat gain directly, but it can cause fluid retention and increase appetite in some people. Weight that appears premenstrually and resolves once your period starts is typically fluid, not fat.
• A rise in basal body temperature: roughly 0.2 to 0.5°C after ovulation, sustained through the luteal phase. This is the basis of temperature-based cycle tracking, though because the rise happens after the egg is released, it confirms ovulation retrospectively rather than predicting it.
• Breast tenderness and swelling, as progesterone prepares breast tissue for possible pregnancy.
• Mood, anxiety and sleep: progesterone is generally calming, but it is the fall before a period that many people find hardest, which is when anxiety, irritability and disturbed sleep tend to peak. Some people are unusually sensitive to progesterone fluctuation and react markedly to changes others barely notice.
• Reduced libido, more often reported at higher levels or on progesterone medication than during a normal cycle.

If low mood, anxiety or sleep problems are affecting your daily life, please speak to your GP rather than treating it as a hormone issue to solve alone.

How progesterone levels change during your menstrual cycle

This is the single most useful thing to understand about progesterone, and the thing most people are not told when they get a result back.

The chart below is built from Forth customer results, plotted by the day of the cycle each sample was taken. It shows the median result for each day, along with the range that most results fall within.

Chart showing progesterone levels by day of the menstrual cycle in nmol/L, from day 1 to day 28, with follicular, ovulation and luteal phases marked

Follicular phase: why progesterone is low

The follicular phase runs from the first day of your period until ovulation, roughly days 1 to 13 of a 28-day cycle. Throughout this stretch, progesterone sits at around 1 nmol/L in Forth results, and often lower.

This is completely expected. There is no corpus luteum yet, so there is nothing producing progesterone in quantity. If you tested on day 3 (a common day for hormone panels, because FSH and LH are best measured then) a progesterone result of around 1 nmol/L is the norm, not a warning sign. A very low first-half result tells you about your timing, not about a problem.

When does progesterone start to rise?

Progesterone begins to climb immediately after ovulation. In Forth data the first clear movement appears around days 13 to 14, with the median edging up from roughly 1 to around 2.6 nmol/L, and the upper end of the range starting to spread widely as some women ovulate earlier than others.

The steep rise comes later. Between day 17 and day 19 the median jumps from under 4 nmol/L to over 23: this is the corpus luteum reaching full production.

When is progesterone at its highest?

Progesterone is at its highest in the mid-luteal phase, around days 19 to 24 of a 28-day cycle. In Forth results, medians across that window sit in the low-to-mid twenties, with day 24 the single highest point at 27.4 nmol/L.

In physiological terms, the peak arrives roughly 7 days after ovulation. That is the whole basis of mid-luteal progesterone testing: it samples the hormone at the moment it should be at its most informative.

If you ovulate later than day 14, which is common and not a problem in itself, your peak shifts later too. This is why the peak is better thought of as “7 days after ovulation” than as “day 21”.

When does progesterone drop before your period?

Progesterone falls sharply in the last few days of the cycle, typically starting about 2 to 4 days before your period, though this varies. In Forth results the median declines from 22.6 nmol/L on day 25 to 13.2 on day 26, and down to around 10 by day 28. The corpus luteum has a fixed lifespan of roughly 10 to 14 days, and when it breaks down, progesterone withdrawal is what triggers the womb lining to shed. The fall causes the period, rather than the other way round.

That withdrawal is also thought to explain much of what people experience as premenstrual syndrome (PMS). Progesterone has a calming effect on the brain, and losing it quickly can be felt as low mood, irritability, poor sleep and anxiety in the days immediately before a period.

When is progesterone at its lowest?

Progesterone is lowest during the follicular phase, particularly around days 5 to 8, where Forth medians dip to roughly 0.75 to 0.9 nmol/L.

Levels are also low, though not quite at their minimum, during your period itself: progesterone has already fallen by then, and that fall is what started the bleed.

Progesterone levels after ovulation, day by day

Cycle days assume ovulation around day 14. If you ovulate later, shift every row later to match.

Normal progesterone levels in women by cycle phase

Because progesterone changes so dramatically across a month, reference ranges are phase-specific. There is no single “normal progesterone level” for a woman that applies all month.

Chart showing normal progesterone reference ranges by cycle phase in nmol/L and ng/mL

nmol/L vs ng/mL: how to convert your result

UK laboratories report progesterone in nanomoles per litre (nmol/L). Many American sources, and some private labs, use nanograms per millilitre (ng/mL). If you are comparing your result against something you have read online, you may be comparing two different units.

Graphic showing how to convert progesterone levels from nmol/L to ng/mL using the conversion factor of 3.18

So a result of 30 nmol/L is 9.4 ng/mL, and a result of 0.5 nmol/L is 0.16 ng/mL.

Normal progesterone levels by age

Age is far less important for progesterone than cycle day, and the chart below needs reading with that in mind.

Bar chart showing median progesterone levels in nmol/L by age bracket for women who are still cycling

These medians combine every day of the cycle together, so the modest upward drift from the late teens into the forties most likely reflects when each group happened to test, rather than a real effect of age. Older women who are still cycling may simply be more likely to be testing for fertility or perimenopause reasons, and therefore more likely to be sampling in the luteal phase.

The practical takeaway is the useful one: your cycle day changes your progesterone far more than your age does. What does change meaningfully with age is your likelihood of ovulating consistently, which is why progesterone becomes less predictable as you approach menopause.

Progesterone levels in men

Men do produce progesterone, in small amounts, from the adrenal glands and testes. It acts mainly as a building block for other steroid hormones, including testosterone.

Male levels are broadly comparable to a woman’s follicular-phase level (typically under 1 nmol/L) and well below the luteal-phase levels a woman reaches each month. Progesterone is not routinely tested in men, and a male hormone panel would usually focus on testosterone, SHBG and the Free Androgen Index instead.

What does my progesterone level mean?

The first question to answer is not “is this number high or low?” but “when in my cycle did I take this sample?” The same number can be entirely normal or worth investigating, depending only on the day.

If you tested in the first half of your cycle, a result under 1 nmol/L is expected and, on its own, reassuring. Results like 0.2, 0.4 or 0.5 nmol/L come up constantly in searches because people find them alarming, but before ovulation the ovary is not producing progesterone in any quantity. Those numbers are entirely normal at that point in the month. A follicular-phase result cannot tell you whether you are ovulating, either way. If you tested mid-luteal, the number becomes informative.

A single result is a snapshot, not a diagnosis. Progesterone varies from cycle to cycle in the same person, and one low reading does not establish a pattern.

What progesterone level confirms ovulation?

A mid-luteal progesterone above roughly 30 nmol/L is the traditional marker consistent with ovulation having occurred.

That threshold comes with a large and under-discussed caveat. In Forth results from cycle days 19 to 23, only about a third of samples clear 30 nmol/L. That does not mean two thirds of those women did not ovulate. Far more likely, it reflects test timing: many people test on a fixed calendar day 21 regardless of their own cycle length, so a substantial share are simply not truly mid-luteal when the sample is taken. This is the single most important caveat attached to any day-21 progesterone result.

What’s a ‘good’ or optimal progesterone level?

There is no universal optimal number, because the question only makes sense once you fix the day of the cycle.

• Mid-luteal, if you want reassurance about ovulation: comfortably above 30 nmol/L
• Mid-luteal, in general terms: within the 13.1 to 46.3 nmol/L reference range
• Follicular phase: under 1 nmol/L is exactly what you want to see
• After menopause, not on HRT: under 0.4 nmol/L is expected

A number that would be reassuring on day 21 would be distinctly odd on day 3, and vice versa. This is why Forth reports progesterone alongside your cycle information rather than against a single fixed range.

Low progesterone

What is considered a low progesterone level?

The answer depends on when you tested, which is why this question is so frequently and so understandably confusing.

• First half of your cycle: almost any result under 1 nmol/L is normal, not low
• Mid-luteal (7 days before your period is due): below the 13.1 nmol/L lower reference limit would be considered low; below 5 nmol/L would prompt a repeat test
• After menopause: low progesterone is expected and does not need treating on its own

Genuinely low progesterone, in the sense that matters clinically, means a low result on a correctly timed mid-luteal sample because that is the only measurement that reflects whether your corpus luteum is doing its job.

Symptoms of low progesterone

Low progesterone is associated with:

• Short cycles, or a short gap between ovulation and your period
• Spotting in the days before your period starts
• Heavy or prolonged periods
• Difficulty conceiving, or early pregnancy loss
• Poor sleep, particularly in the second half of the cycle
• Anxiety, low mood or irritability that follows a cyclical pattern
• Breast tenderness and bloating
• Headaches or migraines linked to the cycle
• Irregular or absent periods

These symptoms overlap heavily with thyroid problems, low ferritin, low vitamin D and raised cortisol, which is why symptoms alone rarely point to a single cause.

Does low progesterone cause belly fat?

Not directly. Progesterone doesn’t drive fat storage around the abdomen the way some articles suggest. What can happen is more indirect: progesterone acts as a mild natural diuretic, so when levels drop you may retain more fluid and feel bloated, which many people experience as weight around the middle, particularly premenstrually.

The more meaningful link is with the oestrogen-to-progesterone balance. When progesterone falls while oestrogen stays relatively high, fluid retention and bloating tend to become more noticeable. Around perimenopause, changes in body composition are also influenced by falling oestrogen, reduced muscle mass and shifting insulin sensitivity.

What causes low progesterone?

Because progesterone depends on ovulation, anything that disrupts ovulation can lower it:

• Anovulatory cycles: cycles where no egg is released, so no corpus luteum forms
• PMOS, where ovulation is often infrequent or absent
• Perimenopause, as ovulation becomes less reliable
• High stress, which can suppress the hormonal signals that trigger ovulation
• Very low body weight, restrictive eating or high training loads
• Thyroid dysfunction, which affects cycle regularity 
• High prolactin, which suppresses ovulation 
• Luteal phase defect, where the corpus luteum produces progesterone for too short a time
• Hormonal contraception, which works partly by preventing ovulation

Forth data shows this relationship clearly. Women with irregular cycles have a day-21 median of 10.7 nmol/L, against 24.0 nmol/L for women with regular cycles.

Chart comparing day-21 progesterone levels in nmol/L between women with regular and irregular menstrual cycles

That gap fits a higher rate of cycles where ovulation didn’t happen, or where a fixed day 21 fell outside the luteal window. If your cycles are irregular, working out your test day from your own cycle length matters even more than usual.

How to increase your progesterone levels naturally

Because progesterone depends on ovulation, the honest framing is this: you cannot raise progesterone directly through lifestyle. What you can do is support the conditions that make regular, healthy ovulation more likely, and progesterone follows from there.

• Manage stress: sustained stress can suppress the brain signals that trigger ovulation. This is the mechanism with the clearest evidence behind it, and also the hardest to act on.
• Eat enough, consistently: under-eating and very low body fat are among the most reliable ways to stop ovulating. Adequate energy intake matters more than any individual food.
• Nutrients that support the process: vitamin B6, magnesium, zinc and vitamin C are involved in hormone production and luteal function. The evidence is modest and mostly relevant where someone is deficient. Supplementing beyond sufficiency doesn’t push progesterone higher.
• Exercise, but not excessively: regular moderate activity supports cycle regularity. Very high training volumes, particularly combined with low energy availability, do the opposite.
• Protect your sleep: hormone signalling follows circadian rhythm, and disrupted sleep is associated with disrupted cycles.
• Reduce alcohol: heavy intake is associated with cycle disruption and anovulation.

If lifestyle changes do help, the effect works through your next ovulation, so meaningful change takes at least one to three cycles to appear in a test result. Anything promising faster results is overselling.

A realistic expectation matters here. These measures help most where a modifiable factor, such as stress, under-eating, over-training, is genuinely part of the picture. Where low progesterone is caused by perimenopause, PMOS or a thyroid problem, lifestyle changes alone are unlikely to be enough, and the underlying cause is what needs addressing.

When to consider HRT

Progesterone or a progestogen is prescribed in several situations: 

• as part of combined HRT for menopausal symptoms
• to protect the womb lining in anyone taking oestrogen who still has a uterus
• sometimes in perimenopause where cycles have become erratic and disruptive
• in some fertility treatment protocols.

Body-identical micronised progesterone (such as Utrogestan) is the form most commonly prescribed in the UK for HRT, and is usually taken at night because of its sedative effect. Whether HRT is right for you depends on your symptoms, your medical history and your own preferences, not on a progesterone number. This is a conversation for your GP or a menopause specialist. Testing gives you and your clinician better information to have that conversation with.

High progesterone

What is considered high progesterone?

Above 46.3 nmol/L in the luteal phase would sit outside the standard reference range. But before treating that as a problem, it is worth understanding something about how progesterone results get labelled.

Around half of all Forth progesterone results carry a “High” flag. For most biomarkers that would be striking. For progesterone it is expected and usually harmless, because the hormone is designed to be near zero in the first half of the cycle and high in the second. A luteal-phase sample will often read above a follicular reference range, and that is the hormone working correctly. 

Chart comparing the percentage of progesterone results flagged as low, healthy or high across all results, pre-menopausal women and post-menopausal women.

The pattern is even stronger after menopause, where results are compared against a much lower reference range. Two thirds of post-menopausal results read High, which in most cases simply reflects HRT, or a sample that sits above a range set very close to zero.

A standalone “High” on progesterone rarely means anything abnormal. The label should always be read together with your cycle day.

Symptoms of high progesterone

Genuinely high progesterone, or the effects of progesterone-containing medication, is associated with:

• Fatigue and drowsiness
• Bloating and fluid retention
• Breast tenderness or swelling
• Low mood or mood changes
• Reduced libido
• Dizziness
• Headaches
• Mild depression in some people

These are largely the same symptoms many women recognise from the luteal phase of a normal cycle, because they are progesterone’s ordinary effects, felt more strongly.

What causes high progesterone?

• Pregnancy: by far the most common explanation for a genuinely high result
• The luteal phase itself: the commonest reason for a “High” flag that isn’t a concern
• Progesterone medication or HRT containing a progestogen
• Fertility treatment, where progesterone support is often prescribed
• Ovarian cysts, particularly a persistent corpus luteum cyst
• Congenital adrenal hyperplasia, a rare inherited condition usually identified through 17-OH progesterone rather than progesterone itself
• Rarely, adrenal or ovarian tumours

Can you have too much progesterone?

In the sense of your own body producing dangerously high levels, this is very unusual outside pregnancy. Your body regulates its own production, and the corpus luteum has a naturally limited lifespan.

Where “too much” becomes a practical question is with prescribed progesterone or progestogens. Doses that are higher than you need can cause drowsiness, bloating, low mood and breast tenderness. If you are taking progesterone and experiencing these, that is a dose conversation to have with your prescriber, not something to change yourself.

Progesterone and fertility

Progesterone matters for fertility in two ways: it indicates whether you ovulated, and it prepares the womb lining for implantation.

• Confirming ovulation: the main clinical use of a progesterone test. A mid-luteal level above roughly 30 nmol/L is consistent with ovulation having occurred that cycle. It works retrospectively — it tells you that you ovulated, not that you are about to.
• Supporting implantation: the progesterone’s second role. The lining needs to be adequately prepared and maintained for a fertilised egg to implant and stay implanted. A luteal phase that is too short, or progesterone that falls away too quickly, can make that harder.

Two things are worth being clear about. First, there is no established “ideal progesterone level for implantation” that you should be aiming for. Second, a single low result does not mean you are not ovulating, and does not mean you cannot conceive.

If you have been trying to conceive for 12 months (or 6 months if you are over 35), or if your cycles are irregular, please see your GP. Progesterone testing is one useful input into a fertility assessment, not a substitute for one.

Progesterone levels in pregnancy

Progesterone is essential in pregnancy. It maintains the womb lining, keeps the uterine muscle quiet so it doesn’t contract, and supports the early stages of implantation and placental development. Levels rise substantially and keep rising into the third trimester.

Chart showing typical progesterone levels in early pregnancy in nmol/L from week 4 to week 12

The typical published first-trimester range is roughly 35 to 141 nmol/L (11 to 44 ng/mL), a very wide band that covers weeks 4 through 12. Two people at the same stage of a perfectly healthy pregnancy can have very different progesterone results, which is why a single value is not used on its own to judge how a pregnancy is progressing. Week-by-week tables circulate widely online, but they imply a precision the evidence doesn’t support, and they cause a great deal of unnecessary worry. What clinicians look at is the overall picture: symptoms, scan findings, and hCG where relevant.

A day-21 result taken when you are pregnant will typically be higher than a normal luteal result, because the corpus luteum is being maintained rather than breaking down. But progesterone is not a pregnancy test, and cannot be used as one. If you are pregnant and worried about a result, speak to your midwife or GP.

Progesterone levels in perimenopause and menopause

Progesterone is often the first hormone to change as you approach menopause, and it usually changes before oestrogen does. The reason is straightforward. Perimenopause brings cycles in which ovulation doesn’t happen: anovulatory cycles. No ovulation means no corpus luteum, and no corpus luteum means no luteal progesterone rise, even if the rest of the cycle looks superficially normal. 

As anovulatory cycles become more frequent, progesterone becomes lower and more erratic. That falling progesterone against relatively maintained oestrogen is thought to contribute to many early perimenopausal symptoms: disrupted sleep, heightened anxiety, heavier or unpredictable periods, and increased breast tenderness.

Forth customer results show the pattern clearly.

Medians combine all cycle days, so pre-menopausal figures look low: most samples were not taken in the luteal phase. The wide pre-menopausal range reflects exactly that spread.

In Forth data, post-menopausal women have a median progesterone of 0.9 nmol/L, compared with 1.6 nmol/L in pre-menopausal women. Both figures look low because most samples are not luteal; the meaningful point is that after menopause, with no corpus luteum forming, low progesterone is entirely expected and permanent.

One important caution about perimenopause specifically: because your cycles are irregular, a single progesterone result is hard to interpret. Perimenopause is generally assessed using the whole hormonal picture: FSH, LH, Oestradiol and your symptoms, rather than progesterone alone.

Progesterone levels on HRT

If you take HRT that includes a progestogen, your progesterone result will reflect the medication as well as your own production.

As the table above shows, post-menopausal women on HRT have a median progesterone almost three times that of those not taking it, and a far wider spread. That is consistent with the progestogen component of combined HRT. The useful context is the reverse reading: a raised progesterone in a post-menopausal woman is most often explained by HRT, not by anything unexpected.

There is no established “optimal” progesterone target for women on HRT in the way there is for, say, thyroid replacement. HRT dosing is guided primarily by symptom control and by protecting the womb lining, not by hitting a number. Your result is useful context for a conversation with your prescriber rather than something to adjust your dose against yourself.

FAQs about progesterone