Understanding Your Progesterone : Oestradiol Ratio

Brought to you by The Female Health Doctor Clinic (Milton Keynes)

Quick summary: Your progesterone (P4) and oestradiol (E2) are two key hormones that naturally rise and fall across the menstrual cycle. Looking at them together can help explain symptoms and timing in your cycle. The ratio is only helpful in the right phase of the cycle and alongside your symptoms.

Table of Contents

What are progesterone and oestradiol?

Oestradiol (E2) is the main form of oestrogen during the reproductive years. It helps build the uterine lining, supports bone, brain and heart health, and affects mood and energy.

Progesterone (P4) rises after ovulation. It calms the uterine lining, supports possible pregnancy, and often has a steadier, calming effect on mood and sleep.

Why might I be offered a P4:E2 assessment?

To check ovulation or the strength of the luteal phase (the 2nd half of your cycle)
To investigate PMS/PMDD, heavy or irregular periods
To explore symptoms during perimenopause
In fertility assessments or treatment planning
To help interpret symptoms when blood tests were taken at a particular time in the cycle

Important: On HRT, we don’t target a specific ratio. We focus on symptoms and using enough progesterone to protect the womb lining.

Timing is everything

Blood results are only meaningful if taken at the right time.

Mid‑luteal (most helpful): ~7 days after ovulation (often day 21 in a 28‑day cycle, but adjust to 7 days before your period starts if your cycle length varies).
Follicular (early cycle): usually days 2–5. Progesterone is normally low here.

If you’re unsure, we can help you plan the best day to test.

Typical ranges (guidance only)

(Ranges vary by lab; your clinician will interpret your exact report and units.)

Cycle phase	Oestradiol (E2)	Progesterone (P4)	What this means
Early follicular	~100–400 pmol/L	<2 nmol/L	Low progesterone is normal before ovulation
Ovulation peak	~500–1200 pmol/L	3–30 nmol/L	E2 peaks; progesterone starting to rise
Mid‑luteal	~400–800 pmol/L	25–80 nmol/L	Adequate ovulation typically shows P4 ≥25 nmol/L

Note: One reading can miss hormone “pulses”. Patterns and timing matter more than a single number.

What is the P4:E2 ratio?

To compare fairly, we convert both hormones to the same unit (nmol/L). If your E2 is in pmol/L, clinicians use a standard conversion.

A higher ratio in the mid‑luteal phase usually means progesterone is appropriately dominant after ovulation.
A lower ratio may suggest a weaker luteal phase or testing at the wrong time.

Rule of thumb (mid‑luteal):

Progesterone ≥25 nmol/L and a P4:E2 ratio above ~100:1 is commonly seen after healthy ovulation.

Ratios are not targets on HRT and are less reliable in perimenopause where hormones fluctuate rapidly.

How should I prepare for a blood test?

Tell us about cycle day, last period start date, and any ovulation predictor kit results.
Note any HRT, contraception, or supplements (e.g., progesterone, DHEA, biotin). Some can affect readings.
Hydrate and eat normally unless your test bundle requires fasting for other markers.

What can affect results?

Irregular or anovulatory cycles (common in perimenopause and some PCOS patterns)
Recent pregnancy or breastfeeding
HRT or contraceptive hormones
Certain medications or supplements (including high‑dose biotin)

Frequently asked questions

Is there an “ideal” ratio for everyone?
No. It depends on where you are in your cycle, your symptoms, and whether you are on HRT.

Can I diagnose “oestrogen dominance” from a single ratio?
Not reliably. Symptoms, cycle timing, ultrasound findings (if needed), and repeated tests give a clearer picture.

What if my progesterone is below 25 nmol/L mid‑luteal?
It might mean a weaker ovulation or that the test wasn’t timed 7 days after ovulation. We’ll interpret this in context and may repeat the test.

How do I calculate my ratio?

Use our calculator here.