Semen analysis calculator (WHO 2021)
Type in the numbers from your semen analysis report and this checks each one against the WHO 2021 (sixth edition) lower reference limits, not the older 2010 figures most tools still use. It also shows where each value sits among men whose partners conceived within twelve months. It does not score fertility.
Semen analysis calculator (WHO 2021)
No sign-up · PrivateWHO 2021 lower reference limit 1.4 mL. The whole sample has to be collected for this to mean anything.
WHO 2021 lower reference limit 16 million/mL. Was 15 million/mL in the 2010 edition.
WHO 2021 lower reference limit 39 million. Leave this blank and it is worked out as volume × concentration.
All moving sperm — progressive plus non-progressive. WHO 2021 lower reference limit 42%. Was 40% in 2010.
Sperm moving forwards. WHO 2021 lower reference limit 30%. The 2010 edition said 32%, so this line moved down.
Normal forms on strict criteria. WHO 2021 lower reference limit 4%. Even in men who conceived within a year, the median was 14%.
WHO 2021 lower reference limit 54%. Was 58% in 2010. Usually only measured when motility is low.
Lower limit 7.2. This one is a carried-forward consensus value, not a 5th centile — WHO has too little fertile-population pH data.
Enter at least one value from your semen analysis report. Every field is optional — reports vary, and vitality and pH are often left off.
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How this is calculated
FormulaThis tool compares each value you enter against the lower reference limits published in the WHO laboratory manual for the examination and processing of human semen, sixth edition (2021). These replaced the 2010 fifth-edition figures that most free interpreters online still run.
The WHO 2021 lower reference limits are: semen volume 1.4 mL; sperm concentration 16 million per mL; total sperm number 39 million per ejaculate; total motility 42%; progressive motility 30%; normal forms (morphology) 4% on strict criteria; vitality 54% live spermatozoa; pH 7.2.
Where those numbers come from. Every limit except pH is the 5th centile of a reference population of 3,589 men from 13 countries on six continents whose partners conceived naturally within twelve months of stopping contraception. pH is the exception: WHO says too little fertile-population pH data exists, so 7.2 is carried forward as a consensus value rather than a measured 5th centile.
What changed from WHO 2010. Volume fell from 1.5 to 1.4 mL. Concentration rose from 15 to 16 million/mL. Total motility rose from 40% to 42%. Progressive motility fell from 32% to 30%. Vitality fell from 58% to 54%. Total sperm number (39 million), morphology (4%) and pH (7.2) are unchanged. A result can therefore be read differently depending on which edition your lab or calculator used.
The logic this tool runs. For each value you enter it reports whether the figure is at or above, or below, its stated limit, and then locates it in the published centile distribution of that same fertile population — so a concentration of 66 million/mL is reported as the median for that group rather than merely "normal". If you leave total sperm number blank it is calculated as volume × concentration, which is how a laboratory derives it, and that calculated row is labelled and excluded from the counts. Progressive motility higher than total motility is rejected as a transcription error, because total motility is progressive plus non-progressive by definition.
What this deliberately does not do. It never returns a bare verdict of "abnormal", never produces a fertility score, and never estimates a chance of conception. The WHO manual states that the 5th centile values "do not define limits between fertile and subfertile men" and that the two populations overlap substantially. By construction, one man in twenty who conceived within a year fell below each of these lines. A value under a limit does not mean infertile; a value above one does not guarantee conception. Only a clinician looking at the whole report, alongside the rest of the couple's assessment, can interpret it.
What a semen analysis actually measures
A semen analysis counts and describes the sperm in one sample, produced on one day. It measures how much fluid there was, how many sperm were in each millilitre of it, how many of those were moving and how well, how many were shaped normally, and — sometimes — how many were alive and how acidic the sample was. That is the whole test. It is the first investigation offered when a couple is having trouble conceiving, and male factors are involved in roughly half of those couples, which is why both partners are assessed rather than just one.
What a semen analysis does not measure is whether a man is fertile. There is no test that does. What exists instead is a set of reference limits: figures describing what was seen in men who are known to have conceived.
Where the WHO 2021 numbers come from
The World Health Organization published the sixth edition of its laboratory manual for the examination and processing of human semen on 27 July 2021. It set out lower reference limits drawn from 3,589 men across 13 countries on six continents. Every one of those men had a partner who conceived naturally within twelve months of stopping contraception. WHO took the 5th centile of that group — the line below which the lowest-scoring 5% of them sat.
That construction matters more than any single number. These limits are not a threshold between fertile and infertile. They are a description of a fertile population, with the bottom twentieth marked off. One in twenty men who fathered a child within a year fell below each of these lines. The manual itself states that the 5th centile values do not define limits between fertile and subfertile men, and that the two groups overlap substantially.
WHO 2021 lower reference limits — and what changed from 2010
The 2021 figures differ from the 2010 fifth edition in five of the eight parameters. Many online interpreters and some laboratory report templates still use the older set, so it is worth checking which edition your report cites.
| Parameter | WHO 2021 (6th ed) | 95% CI | WHO 2010 (5th ed) | Median in the fertile group |
|---|---|---|---|---|
| Semen volume | 1.4 mL | 1.3–1.5 | 1.5 mL | 3.0 mL |
| Sperm concentration | 16 million/mL | 15–18 | 15 million/mL | 66 million/mL |
| Total sperm number | 39 million per ejaculate | 35–40 | 39 million | 210 million |
| Total motility (PR + NP) | 42% | 40–43 | 40% | 63% |
| Progressive motility (PR) | 30% | 29–31 | 32% | 55% |
| Normal forms (morphology) | 4% | 3.9–4.0 | 4% | 14% |
| Vitality (live spermatozoa) | 54% | 50–56 | 58% | 78% |
| pH | 7.2 | consensus value | 7.2 | not published |
Look at the last column before you look at anything else. Among men who conceived within a year, the median morphology was 14% normal forms — meaning the typical fertile man in that study had 86% of his sperm classified as abnormally shaped. Strict morphology criteria are unforgiving by design. A result of 5% is not a near-miss on a scale where 100% is the target.
The words on your report
Laboratories use descriptive terms that sound far more final than they are. Oligozoospermia means the concentration came in below the reference limit. Asthenozoospermia means reduced movement. Teratozoospermia means fewer normally-shaped sperm. Necrozoospermia means a low proportion of live sperm. Azoospermia means no sperm were found in the sample — which has treatable causes including obstruction and hormonal problems, and often still allows sperm to be retrieved surgically for ICSI. Each word describes one measurement on one sample. None of them is a diagnosis.
Why one sample is not an answer
Semen parameters vary enormously in the same man from one week to the next. A fever six weeks ago, a heavy cold, a very short or very long gap since the last ejaculation, or simply spilling part of the sample during collection will all move the numbers. WHO asks for two to seven days of abstinence before the sample precisely because both extremes distort the result: too short lowers volume and count, too long lowers motility and vitality.
This is why NICE advises repeating an abnormal first result, ideally about three months later, since a full cycle of sperm production takes roughly that long. The exception is a result showing azoospermia or a severe deficiency, where NICE says to repeat as soon as possible rather than waiting.
What happens after the test
A semen analysis is the first test, not the last. If results are persistently below reference limits, the next steps usually include a physical examination, hormone blood tests, sometimes a scrotal ultrasound, and in some clinics sperm DNA fragmentation testing. Many of the causes found are treatable or workaroundable, and treatments including IUI, IVF and ICSI exist specifically for results well below these limits.
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Sources
- WHO laboratory manual for the examination and processing of human semen, sixth edition — World Health Organization, accessed
- Lower reference limits for semen characteristics (WHO 6th edition centile table) — Andrology Laboratories, Manchester University NHS Foundation Trust, accessed
- The Sixth Edition of the WHO Manual for Human Semen Analysis: A Critical Review and SWOT Analysis — Life (Basel) 2021;11(12):1368, via PubMed Central, accessed
- Fertility problems: assessment and treatment (NG257) — investigation of fertility problems — National Institute for Health and Care Excellence, accessed