Estradiol: reference ranges across cycle phases and when to test

Estradiol (E2) is the most potent estrogen in women of reproductive age. It regulates the menstrual cycle, supports bone density, and affects the cardiovascular system and mood. Estradiol maintains normal endometrial function, preserves mucosal integrity, and provides partial cardiovascular protection during the reproductive years. On a lab report, the value often raises questions: what counts as normal? Why does the result differ on different days of the cycle? What does a low E2 in your 40s actually mean? Here is what you need to know — but one point upfront: E2 is always interpreted together with FSH and LH and in relation to cycle phase, not as a standalone number.

Diagnosing ovarian status or the menopausal transition from a single estradiol value is not possible. What follows is what is useful to understand about your own results before speaking with a clinician. This article does not replace a medical consultation and contains no treatment recommendations.

E2, E1, and E3: three forms of estrogen

Estrogens are not a single hormone but a family of related compounds. Three forms appear in clinical practice.

Estradiol (E2) is the dominant estrogen during reproductive life. It is synthesised primarily in the ovaries and drives most of the effects we associate with estrogens: cycle regulation, mucosal support, and bone protection. It is the form measured in most standard hormonal panels.

Estrone (E1) is a less active form that becomes the predominant estrogen after menopause. It is synthesised mainly in adipose tissue from androgens — which is why E1 levels in postmenopause tend to be higher in women with greater body mass. It is rarely measured outside of specialised studies or HRT monitoring.

Estriol (E3) is the weakest of the three. It is produced by the placenta and is the main estrogen of pregnancy. It is not measured in routine panels outside of pregnancy; during pregnancy it forms part of second-trimester screening (the “triple test”).

When a lab report simply reads “estradiol” or “estradiol E2,” it refers to E2. This is the clinically meaningful marker for women of reproductive and perimenopausal age.

Estradiol reference ranges by cycle phase

E2 values vary substantially depending on the day of the cycle. This is not a flaw in the test — it is physiology: estradiol is the cycle’s working molecule and rises predictably from a trough at the start of the follicular phase to a peak just before ovulation. Comparing a result to a reference range without knowing the cycle phase is one of the most common interpretation errors.

Phase	Estradiol (pg/mL)	Estradiol (pmol/L)
Follicular (days 2–5)	20–150	70–550
Ovulatory (mid-cycle)	100–400	370–1,470
Luteal	30–200	110–735
Postmenopause	< 30	< 110

The ranges above are approximate and correspond to typical reference intervals. Individual laboratories may report slightly different values depending on the assay method and reagents — always compare your result to the reference range printed on your own report. The units pg/mL and pmol/L are related by a factor of 3.671: to convert pg/mL to pmol/L, multiply by 3.671.

Perimenopause and postmenopause

The decline in E2 after 40 is not a single event but a gradual process that unfolds over years. As ovarian reserve decreases, estradiol production falls. The pituitary responds by raising FSH in an attempt to push the ovaries to keep responding. This is why the typical laboratory pattern in perimenopause is a progressively rising FSH alongside falling E2.

E2 levels in perimenopause can fluctuate considerably from cycle to cycle: they do not decline in a straight line but in jumps. One normal result does not exclude a menopausal transition; one low result does not confirm it on its own.

The symptoms most commonly associated with declining E2 — hot flushes, night sweats, sleep disturbance, mucosal dryness, mood changes — can appear before E2 has dropped below the lower limit of the reference range. The clinical picture and the trend across measurements matter more than any single value. For a detailed account of how FSH and LH reflect menopausal status and when to measure them, see the companion article FSH and LH: assessing menopausal status.

HRT and estradiol monitoring

If you are taking oral hormone replacement therapy (HRT tablets), routine measurement of plasma E2 is generally not informative. After an oral tablet is absorbed, estradiol concentration in the plasma fluctuates sharply over the course of the day due to hepatic first-pass metabolism — a single blood draw bears little correlation to the actual tissue-level effect of the medication. For this reason, the effectiveness of oral HRT is assessed clinically: by symptoms, not by a number on a lab report.

For transdermal HRT (patches, gels), monitoring E2 can be appropriate — for example, to confirm adequate absorption or when symptoms persist despite therapy. Plasma E2 reflects transdermal delivery far more consistently than it does oral delivery. The decision always rests with the clinician managing your therapy.

The NAMS 2022 position statement notes that routine E2 monitoring during established HRT is not the standard of care, but may be useful in specific clinical situations — for example, atypical symptoms or suspected inadequate absorption of a transdermal preparation.

Self-adjusting or evaluating the effectiveness of HRT based on E2 values is not recommended. If you are on HRT and are uncertain whether E2 monitoring is appropriate, ask the clinician overseeing your treatment.

When to test estradiol

For a baseline assessment of ovarian status and an approximate estradiol level, the optimal time is days 2–5 from the start of menstruation (early follicular phase). Values are most stable during this “basal” window and most suitable for comparison across repeat measurements.

Regarding time of day: there is no strict requirement, but morning sampling is standard practice, as sex hormone secretion follows a circadian rhythm. For reproducibility across repeat tests, aim to sample at the same time each visit.

One important point: E2 should not be measured for assessment of endogenous ovarian function while on methods that systemically suppress the hypothalamic-pituitary-ovarian axis — combined oral contraceptives (COCs), the combined vaginal ring, the combined patch, depot injectable progestogens, and GnRH agonists. These suppress your own hormone production, and the result will not reflect your natural hormonal status. Levonorgestrel intrauterine devices, by contrast, act primarily locally; most users continue to ovulate, and E2/FSH values are usually interpretable — if in doubt, discuss with your clinician.

Common interpretation pitfalls

A single number without cycle phase and FSH is not diagnostic. E2 50 pg/mL in the follicular phase is a different finding from E2 50 pg/mL in the luteal phase. And E2 50 pg/mL alongside FSH 40 IU/L tells a very different story from E2 50 pg/mL alongside FSH 6 IU/L. Without context, the number cannot be interpreted.

Combined oral contraceptives change the entire picture. COCs suppress the hypothalamic-pituitary-ovarian axis: endogenous E2 will be artificially low, as will FSH and LH. Assessing hormonal status while taking COCs is uninformative. Testing should be deferred until after the contraceptive is stopped.

Stress and intense exercise have less impact than FSH but can cause fluctuation. E2 is relatively more stable than cortisol, but under extreme physiological stress, significant underweight, or functional hypothalamic amenorrhoea it can fall along with FSH and LH. A single low value in the context of illness or exhaustion is not grounds for conclusions without a trend and clinical assessment.

Wrong timing is a common cause of unexpected results. E2 400 pg/mL is a perfectly normal value for the day of ovulation, but looks alarming if you believed you were testing in the early follicular phase. Always record the cycle day on the test request form and on the report.

When working through the differential diagnosis of cycle irregularities or amenorrhoea, clinicians typically assess several hormones together — including TSH, prolactin, FSH, and LH — rather than E2 alone.

How HealthLab helps track trends

In perimenopause, estradiol is most informative not as an isolated data point but as a trend: is it falling gradually or in jumps, and do its fluctuations correspond to changes in FSH? A single measurement is a snapshot; several measurements over time reveal the real picture.

Another common problem is accumulating paper lab reports and manually transferring values into spreadsheets. Most people stop doing this after the second or third test, and the trend is lost.

HealthLab automatically recognises E2, FSH, LH, and other hormones from PDF lab reports issued by any laboratory, and builds a trend chart over time. You can see immediately how the value is changing from cycle to cycle — without manual data entry or spreadsheets. All values are stored in one place and viewable alongside reference ranges.

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Frequently asked questions

Can a single E2 value assess menopausal status?

No. First, E2 naturally fluctuates from cycle to cycle, especially during perimenopause. Second, one low result does not confirm menopause — at minimum a paired measurement with FSH and a clinical assessment of symptoms are required. Third, for women over 45 with typical symptoms, NICE NG23 supports a clinical diagnosis without mandatory testing. E2 is a supporting marker, not a standalone diagnostic criterion.

Which day of the cycle is correct for a baseline E2?

For a baseline assessment, days 2–5 from the start of menstruation (early follicular phase). Values are most stable during this window and most suitable for comparison across visits and across different laboratories. Other days may be ordered for specific indications — for example, ovulation monitoring (mid-cycle) or luteal phase assessment. If your cycle is irregular or absent, the appropriate timing is determined by your clinician. Always record the cycle day or the date of your last period on the test request form.

Is E2 monitoring needed during HRT?

It depends on the form of therapy. With oral HRT, routine plasma E2 measurement is generally not informative: sharp fluctuations after a tablet is taken do not reflect the actual tissue-level effect. With transdermal HRT (patch or gel), measurement is sometimes appropriate — to confirm adequate absorption. The decision always rests with the clinician managing your therapy.

Do combined oral contraceptives affect E2?

Yes, substantially. COCs suppress endogenous estradiol production through their effect on the hypothalamic-pituitary-ovarian axis. E2 levels measured while taking COCs do not reflect natural hormonal status and cannot be used to assess ovarian reserve or menopausal transition. Testing should be deferred until after the contraceptive is stopped.