How do you calculate the P:E ratio?

The P:E ratio is calculated by dividing progesterone by estradiol, both converted to the same unit (nmol/L). For progesterone in pg/mL, divide by 3.18 to convert. For estradiol in pg/mL, divide by 3.671 to convert. Then divide progesterone nmol/L by estradiol nmol/L.

What does a low P:E ratio mean?

A low P:E ratio indicates estrogen dominance, meaning progesterone is insufficient relative to estradiol. Common causes include anovulatory cycles, chronic stress, xenoestrogen exposure, impaired liver detoxification, dysbiotic gut microbiome, and excess body fat. Symptoms include mood instability, poor sleep, weight gain, and irregular cycles.

When should I test progesterone and estradiol for accuracy?

For cycling women, test on days 19 to 21 of a 28-day cycle, 7 days after presumed ovulation. Testing at other times will show falsely low progesterone because progesterone is only meaningfully elevated during the luteal phase. For post-menopausal women or those on HRT, draw at any time.

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Progesterone to Estradiol Ratio Calculator

Q: What is the optimal Progesterone to Estradiol ratio?

In functional medicine, a P:E ratio between 100 and 600 is considered optimal during the luteal phase of the menstrual cycle. Below 100 indicates estrogen dominance. Above 600 suggests estrogen deficiency relative to progesterone, which becomes more common in perimenopause and post-menopause.

The P:E ratio is one of the most clinically meaningful numbers in functional hormone analysis. Standard lab ranges tell you whether each hormone is in range in isolation. The ratio tells you whether they are balanced relative to each other, which is what actually drives symptoms.

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Progesterone to Estradiol
Ratio Calculator

100–600

Optimal Range

nmol/L

Calculated Unit

5 Bands

Color-Coded Result

Functional

Not Conventional

Enter Your Lab Values

Progesterone

Most US labs report in ng/mL. Multiply ng/mL by 1000 to get pg/mL.

Estradiol (E2)

Standard US labs report in pg/mL. European labs use pmol/L. Divide pmol/L by 3.671.

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Functional Reference Bands

Below 50Severely Estrogen Dominant

50 to 99Estrogen Dominant

100 to 600Optimal

601 to 1000Elevated. Possible Estrogen Deficiency

Above 1000Severely Elevated

Why the ratio matters more than either value in isolation.

Standard lab reference ranges are built on population averages. They tell you whether your value falls within the range seen in most people, not whether it is optimal for you. A woman can have an estradiol of 80 pg/mL and a progesterone of 0.8 ng/mL and both will read as normal. But the ratio is severely imbalanced, and she will feel it.

The P:E ratio gives a single number that reflects the relative balance between the two primary female sex hormones. This balance governs mood, sleep, cycle regularity, metabolic function, thyroid conversion, and long-term tissue health.

In functional medicine

A ratio between 100 and 600 is generally considered optimal during the luteal phase. Below 100 indicates estrogen dominance. Above 600 suggests estrogen deficiency relative to progesterone, which becomes more common in perimenopause and post-menopause.

What Drives Imbalance

Causes of Low Ratio (Estrogen Dominance)

Anovulatory cycles. No ovulation means no corpus luteum and no progesterone surge.
Chronic stress. Cortisol competes with progesterone for the same receptor and is synthesized from the same precursor.
Xenoestrogen exposure. Plastics, pesticides, and synthetic fragrances bind estrogen receptors.
Impaired liver detoxification. The liver clears estrogen metabolites. Sluggish Phase I or II pathways allow recirculation.
Dysbiotic gut microbiome. The estrobolome can deconjugate cleared estrogens and return them to circulation.
Excess body fat. Adipose tissue converts androgens to estrogen via aromatase.

Causes of High Ratio (Estrogen Deficiency)

Perimenopause and menopause. Ovarian estradiol production declines sharply.
Hypothalamic amenorrhea. Low body fat or extreme exercise suppresses the HPG axis.
Ovarian insufficiency or premature ovarian failure.
Aggressive progesterone supplementation without estrogen support.
Post-birth control syndrome. Synthetic progestins suppress the HPG axis and recovery can be slow.
Chronic under-eating or low dietary fat. Steroid hormone synthesis requires cholesterol.

When to Test for Accuracy

Timing is critical. Progesterone is only meaningfully elevated during the luteal phase, the 10 to 14 days after ovulation. Drawing labs on day 3 of your cycle will show low progesterone regardless of how healthy your hormones are, because that is where it should be at that point in the cycle.

Cycling Women

Draw on days 19 to 21 of a 28-day cycle, 7 days after presumed ovulation. If your cycle is longer or shorter, adjust accordingly. The target is 7 days post-ovulation.

Perimenopausal Women

Draw mid-luteal if cycles are still present. If irregular, draw on any day and note cycle day on the lab requisition for context.

Post-Menopausal or On HRT

Draw at any time. Optimal ranges shift. A ratio of 100 to 300 is generally targeted for women on bioidentical HRT.

The P:E ratio is one data point. A complete functional hormone review looks at 31 markers including SHBG, DHEA-S, cortisol, thyroid cascade, and metabolic markers, and reads them in sequence using the MARCH method. One number does not tell the whole story. See the full Lab Intelligence service →

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