Hormones
Normal LH:FSH Ratio: Reading a UK Number
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed September 20266 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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In the first half of a cycle, Gloucestershire Hospitals reads LH 1 to 12 IU/L and FSH 1 to 9 IU/L, so a normal ratio sits around 1. The ratio only carries meaning on days 1 to 5 of your cycle. At ovulation LH alone reaches 104, which lifts the ratio far above 2 in a perfectly ordinary month.
Not sure which markers you need? Build your test →Your LH is 14 and your FSH is 5. You divide one by the other, get 2.8, and find a dozen pages telling you that anything over 2 points to PCOS.
The first question nobody asks you is which day of your cycle the blood was taken. It decides almost everything about that number. This guide covers the UK ranges, the day-1-to-5 rule, and what NHS labs themselves say about the ratio.
1. What is a normal LH:FSH ratio in the UK?
LH and FSH are the two signals your pituitary sends to the ovaries or testes. The pituitary is a pea-sized gland under your brain. UK labs report both in international units per litre, written IU/L.
There is no published reference range for the ratio itself. You work it out from the two numbers, so it is worth seeing them side by side.
| Phase | LH | FSH | Rough ratio |
|---|---|---|---|
| Follicular | 1 to 12 | 1 to 9 | around 1 |
| Ovulatory | 16 to 104 | 6 to 26 | up to about 4 |
| Luteal | 1 to 12 | 1 to 9 | around 1 |
| Post-menopausal | 16 to 66 | 30 to 118 | below 1 |
| Adult male | 1 to 8 | 1 to 7 | around 1 |
Read the last column carefully. A healthy ratio is not one number. It is four different numbers depending on when you sampled.
2. Why cycle day decides your ratio
Because LH spikes and FSH does not, at least not by as much.
Mid-cycle, LH surges to trigger ovulation. Gloucestershire reads it up to 104 IU/L in that window while FSH tops out at 26. Do the division and you land around 4. Nothing is wrong. You simply drew blood on the day of the surge.
This is why NHS labs ask for a specific window. North Bristol NHS Trust states it in one line for LH: for females, sample at day 1 to 5 of cycle recommended. Day 1 is the first day of proper bleeding, not spotting.
A ratio worked out from a random day is not a bad result. It is not a result at all.
One more thing can shift both numbers, and it is sitting in a lot of bathroom cabinets. Gloucestershire asks that anyone on high-dose biotin therapy, meaning more than 5mg a day, waits at least 8 hours after the last dose before sampling. Biotin is the B vitamin sold for hair and nails, and it interferes with the analyser rather than with your hormones. Our guide to supplements that affect blood tests covers the rest.
3. What a raised ratio does and does not mean
Here is the sentence the internet leaves out, from the lab handbook itself.
“LH:FSH ratios are often raised (>2.5) in samples collected days 1-5 of the menstrual cycle in women with polycystic ovarian syndrome (PCOs) but can be normal.”
— Gloucestershire Hospitals NHS Foundation Trust, pathology
Three things follow from that one sentence.
- The threshold the lab names is 2.5, not 2.
- It applies to a days 1 to 5 sample and nothing else.
- It can be normal in PCOS, so a ratio under 2.5 rules nothing out.
That last point is the reason the ratio is not a diagnostic test. PCOS is assessed on cycle pattern, signs of raised androgens and ovarian appearance, with a clinician weighing all of it. Our PCOS blood test guide walks through the markers that conversation usually involves.
The lab also asks for context with the sample: day of cycle, menstrual history, fertility problems, and any signs of hyperandrogenisation. A number sent without that is a number nobody can read.
4. After 45, the pair flips over
Look back at the table. After menopause, FSH runs 30 to 118 and LH runs 16 to 66. FSH is now the bigger of the two, so the ratio drops below 1.
That flip is real, but NICE does not want it used as a test. Guideline NG23 says FSH testing is often done unnecessarily in women over 45, and gives the reason directly.
“FSH fluctuates considerably over short periods of time during the years leading up to menopause and so blood levels are not a helpful addition to what is a clinical diagnosis.”
— NICE guideline NG23, menopause
NG23 keeps a narrow window for the test. Recommendation 1.2.5 says to consider an FSH test only in women aged 40 to 45 with menopausal symptoms including a change in their cycle, or in women under 40 where menopause is suspected. It also says not to use FSH in anyone on combined contraception or high-dose progestogen, because those change the reading.
Our FSH levels by age guide covers how that number drifts through your forties, and the menopause hub gathers the rest.
5. Which blood test reports your LH and FSH
The markers are LH and FSH, both in IU/L. Helvy's Hormone Balance panel (£99) reports both, alongside SHBG, total testosterone and the free androgen index. The kit tells you which days to test, and the report reads your values against the day you sampled.
Two honest boundaries. The panel does not include oestradiol or progesterone, so if a clinician wants oestrogen tracked directly, that is a separate conversation. And a single reading is a snapshot, because both hormones move through the month.
Our normal LH levels guide reads that hormone on its own, and the hormone test timing calculator works out your sampling window from your last period. The build-my-test tool helps you pick markers.
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See LH and FSH read against the day you sampled
Helvy's home blood tests report both hormones in UK units with plain-English context, timed to your cycle rather than to whenever the kit arrived. Samples are processed by UKAS-accredited UK labs.
If the FSH on its own is what was flagged rather than the ratio, our guide to what a high FSH result means takes that number apart.
Frequently asked questions
What is a normal LH to FSH ratio?
In the follicular phase, Gloucestershire Hospitals reads LH 1 to 12 IU/L and FSH 1 to 9 IU/L, which puts a normal ratio around 1. There is no published reference range for the ratio itself, only for the two hormones behind it.
Does an LH:FSH ratio over 2 mean PCOS?
No. Gloucestershire Hospitals says the ratio is often raised above 2.5 in days 1 to 5 samples in women with PCOS, but can be normal. It is not a diagnostic test, and a clinician weighs cycle pattern and symptoms alongside it.
Which day of my cycle should LH and FSH be tested?
North Bristol NHS Trust recommends sampling at day 1 to 5 of the cycle. Day 1 is the first day of proper bleeding. A sample taken mid-cycle catches the LH surge and gives a ratio that means nothing.
Why is my LH so much higher than my FSH?
The most common reason is timing. LH surges to trigger ovulation and can reach 104 IU/L mid-cycle while FSH stays under 26. On days 1 to 5 the two sit much closer together.
What happens to the ratio after menopause?
It usually falls below 1. Gloucestershire reads post-menopausal FSH at 30 to 118 IU/L against LH at 16 to 66, so FSH becomes the larger of the two. NICE still advises against using FSH to identify menopause in women over 45.
Can the contraceptive pill change my LH and FSH?
Yes. NICE guideline NG23 says not to use an FSH test in women taking combined oestrogen and progestogen contraception or high-dose progestogen, because these affect the measurement. Discuss timing with a qualified clinician first.
Related guides
Normal LH Levels UK
The surge hormone, read on its own.
FSH Levels by Age UK
How the number drifts through your forties.
PCOS Blood Test UK
The markers behind a PCOS conversation.
Free Androgen Index UK
The calculated number read alongside LH and FSH.
Irregular Periods Blood Test UK
What gets checked when the cycle stops being predictable.
Blood Test Reference Ranges UK
Why normal on a lab report is a population range, not a target.