The LH to FSH Ratio: What It Signals in PCOS, Perimenopause and Fertility Testing, When to Draw It, and How to Calculate It

Luteinizing hormone and follicle-stimulating hormone are released together by the pituitary, and the LH:FSH ratio is simply one divided by the other from a single blood draw. It only means something when the draw happens at baseline — cycle day 2–4 in a woman who is cycling and not on hormonal contraception — because that is the one window in which both hormones are quiet and comparable. There, FSH is normally at or slightly above LH, so the usual ratio is about 1 or below. The pattern people search for is the reverse: LH two or three times FSH, which is common in polycystic ovary syndrome and was once treated almost as a test for it. It is not. The PCOS criteria in use today — Rotterdam and the 2023 international guideline — rest on ovulatory dysfunction, androgen excess, and ovarian morphology or AMH; the ratio is supporting evidence a clinician may note, not a line a result has to cross. And when the ratio falls well below 1 because FSH is high, the useful information is the FSH number itself, which is how ovarian reserve and the menopausal transition are read.

Every LH:FSH interpretation assumes an early-follicular sample. LH rises several-fold for roughly a day around ovulation — the surge that ovulation predictor kits detect — so a sample drawn mid-cycle will show LH far above FSH in a woman whose hormones are entirely normal. Later in the cycle both hormones fall as progesterone rises. The FSH vs LH guide covers what each hormone does across the cycle; for the ratio, the practical rule is: day 2, 3 or 4 counting the first day of full flow as day 1, LH and FSH from the same tube.

Three situations make the ratio uninterpretable regardless of day: hormonal contraception (the pill, patch, ring, hormonal IUD in some women) suppresses both hormones; pregnancy and breastfeeding change them; and irregular or absent cycles — the very situation in which PCOS is suspected — mean there may be no day 2–4 to aim for. In that last case clinicians draw on any day and interpret the pair alongside estradiol, progesterone and androgens rather than leaning on the ratio.

Day 2–4 sample, cycling woman, no hormonal contraception. The LH:FSH ratio calculator returns the band for your numbers.

Two cautions. Published studies disagree on where "elevated" starts — some use 2, some 2.5 or 3 — and a sizeable fraction of women with PCOS have a normal ratio, which is one reason it was never adopted as a criterion. And the absolute values matter as much as the ratio: a ratio of 2 built from an LH of 4 and an FSH of 2 is not the same finding as one built from an LH of 18 and an FSH of 9.

In PCOS the pituitary tends to release LH in faster, larger pulses while FSH stays relatively low, which is why LH often outruns FSH on a baseline draw. That LH excess also drives the ovarian theca cells to make more androgens, which connects the ratio to the acne, hair growth and ovulation problems that define the condition. It is a real physiological signal — just not a reliable one: a meaningful share of women with PCOS have a normal ratio, particularly at higher body weights, and the ratio is easily inflated by mistimed sampling.

That is why the diagnostic criteria leave it out. The Rotterdam criteria (2003) require two of three: irregular or absent ovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound, after excluding other causes. The 2023 international evidence-based guideline keeps that structure and allows an elevated AMH in place of ultrasound in adults; it does not include the LH:FSH ratio. If your ratio is high, the questions that actually settle the diagnosis are about your cycles, your androgen levels (total and free testosterone, SHBG, DHEA-S), and an ultrasound or AMH — the markers the Women's Hormone Panel draws together.

As the ovaries' follicle pool declines, the pituitary raises FSH to recruit what remains, so day-2–4 FSH climbs through the late reproductive years and the menopausal transition — the STRAW+10 staging system uses variable then persistently elevated FSH, alongside cycle changes, to mark those stages. That rising FSH pushes the LH:FSH ratio well below 1, but the ratio is the wrong way to look at it: the ASRM committee opinion on ovarian-reserve testing reads the day-2–4 FSH together with estradiol (a high estradiol can suppress FSH into the normal range and hide the signal) and treats AMH as the more stable marker because it barely varies across the cycle. Reserve markers predict how the ovaries respond to fertility treatment; they are poor predictors of whether a woman will conceive naturally, and a single high FSH is confirmed on a later cycle before anyone acts on it.

Men make LH and FSH continuously rather than in a cycle, and the question their levels answer is different: when total testosterone is low, is the problem in the testes or upstream in the pituitary? The Endocrine Society guideline reads the two hormones individually. High LH and FSH with a low testosterone point to primary hypogonadism — the testes are not responding (Klinefelter syndrome, prior injury, chemotherapy or radiation, mumps orchitis). Low or normal LH and FSH with a low testosterone point to secondary hypogonadism — a weak pituitary signal, with obesity, opioids, high prolactin, pituitary disease and exogenous testosterone or anabolic steroids the common causes; prolactin and iron studies are typical next tests. Dividing one by the other adds nothing to that reading. The Men's Hormone Panel draws LH and FSH with total and free testosterone for exactly this question.

• For the ratio itself: LH ($36.99) and FSH ($29.99) from one draw on cycle day 2–4; no fasting; one $6 fee covers the order. Add estradiol ($35.99) — a high estradiol changes how a "normal" FSH is read.
• Suspected PCOS: the ratio plus the markers the criteria actually use — total and free testosterone, SHBG, DHEA-S, AMH — which the Women's Hormone Panel bundles. Irregular cycles make the day-2–4 rule hard to follow; draw anyway and let the clinician interpret the whole set.
• Fertility planning or reserve: Women's Fertility Essentials ($119.99) — AMH, FSH, LH, estradiol and progesterone — with FSH, LH and estradiol drawn on day 2–4.
• Perimenopause symptoms: FSH and estradiol, repeated in a later cycle if the first is high; the ratio is incidental.
• A man with low testosterone: LH, FSH and total testosterone (plus prolactin) — the Men's Hormone Panel; draw between 7 and 10 a.m.

Results post to your portal in 1–4 business days with the reviewed reference ranges; the calculator takes the two numbers from any lab report.