FIB-4 calculator
FIB-4 estimates how likely it is that your liver already has advanced scarring. It reads four values you may already have on a blood report: your age, two liver enzymes and your platelet count.
Fill in the four fields and your FIB-4 score will appear here.
The calculation runs in your browser and nothing you enter is sent to us or stored. FIB-4 decides who needs further testing. It does not measure your liver.
The score
What FIB-4 is
FIB-4 is a fibrosis index: four routine values combined into one number that estimates how likely advanced liver scarring is. It was published in 2006 for people with HIV and hepatitis C, and has since been validated far more widely, including in fatty liver disease, which is what most people who reach for it today have.
The formula fits on one line: your age multiplied by your AST, divided by your platelet count multiplied by the square root of your ALT. Nothing in it is fitted to a population, so unlike a cardiovascular risk model there is no country calibration and no Swiss version of the number.
Its strength is negative, in the useful sense. A low score is good at ruling advanced fibrosis out, which is why the European guidelines for fatty liver disease put FIB-4 first: it costs nothing on top of a blood test already taken, and only the people who do not score low go on to a scan.
What it reads
The four things the score uses
Every input is on a standard blood report. Three of the four move the score the way you would expect, and the fourth, platelets, is the one most people have never thought of as a liver value.
Age
Age multiplies the result directly, so a 70-year-old and a 40-year-old with identical blood results do not get the same number. That is also why the lower cut-off moves upward from 65, and why a low score before 35 proves less than it looks.
AST
Aspartate aminotransferase, written ASAT or GOT on Swiss reports. It rises when liver cells are damaged and it multiplies the score, so a higher AST raises it. It is not liver-specific: muscle releases it too, so hard exercise in the days before a blood draw can lift it.
ALT
Alanine aminotransferase, written ALAT or GPT. More liver-specific than AST, and it divides the score through a square root, so a higher ALT lowers it. That looks backwards until you see what the pair measures: as fibrosis advances, AST rises relative to ALT.
Platelet count
The count falls as scarring progresses, because a stiffening liver raises the pressure in the portal vein and the spleen holds more platelets back. It divides the score, so a lower count raises it, and it carries more of the signal than either enzyme.
What counts as a low score at your age
Age sits in the numerator, so the same liver produces a higher FIB-4 with every passing year. A 70-year-old with an AST of 30, an ALT of 35 and a platelet count of 250 scores 1.42: low from 65 onwards, indeterminate below it. Only the lower cut-off moves, because it is the one doing the ruling out.
| Age | Low | Indeterminate | High |
|---|---|---|---|
| under 65 | below 1.30 | 1.30 to 2.67 | above 2.67 |
| 65 and over | below 2.00 | 2.00 to 2.67 | above 2.67 |
The upper cut-off stays at 2.67 in both age groups. Applying the standard 1.30 from 65 onwards would send a large number of people with healthy livers for a scan, which is why the age-adjusted lower cut-off exists.
Who the score applies to
FIB-4 was built to triage adults who have a reason to ask about liver scarring. Outside that setting it answers a question nobody asked, and several common conditions move it for reasons that have nothing to do with the liver.
It applies if
- You are an adult with a recent liver panel and a recent full blood count
- You have a reason to ask: fatty liver on a scan, raised liver enzymes, type 2 diabetes, obesity or regular alcohol use
- Your enzymes are at their usual level rather than in the middle of a flare
It does not apply if
- You have an acute hepatitis or any illness that has sent your enzymes into the hundreds: the score reads chronic, stable values
- Your platelet count is low or high for a reason of its own, such as a blood disorder, a recent infection or a medication that affects it
- You already have a diagnosis of cirrhosis: the question FIB-4 asks is settled
- You are pregnant, or you are under 18
FIB-4 also says nothing about the cause. Alcohol, metabolic fatty liver disease, viral hepatitis and autoimmune liver disease all raise the same score, and what to do about them differs completely. That is a reason to read the result with a doctor, not a reason to ignore it.
The units, the way Swiss labs report them
AST and ALT go in as units per litre, which is what every Swiss laboratory reports. Your report may name them ASAT and ALAT, the international convention, or GOT and GPT, the older German one. They are the same two enzymes under either name.
Platelets are where a mix-up is easy. Swiss reports write the count in G/L, meaning billions per litre, so a normal result reads as 150 to 400. The same count in the American convention is 150,000 to 400,000 per microlitre. Enter 250, not 250,000: this calculator refuses a figure in the thousands rather than dividing your score by a thousand and printing a reassuring number.
One check-up, four values
The four numbers rarely sit on the same printout: the two enzymes come from a liver panel and the platelet count from a full blood count. Both are standard on a comprehensive check-up, so if you have had one recently they are already in your file.
The limits
What FIB-4 cannot tell you
FIB-4 is good at deciding who needs a scan. It is poor at describing what is happening inside one person's liver.
The middle band is wide
About a third of everyone tested lands between the two cut-offs, where the score has ruled nothing in and nothing out. That is not a flaw in the formula: it is why the guidelines pair it with a second test rather than acting on it alone.
Age pulls it in both directions
Because age multiplies the result, a healthy 70-year-old can cross 1.30 on entirely normal enzymes and platelets, which is what the age-adjusted cut-off corrects for. Below 35 the opposite applies: the score comes out low almost whatever sits behind it.
It is one blood draw
Enzymes move from week to week and a platelet count dips after an infection. A single FIB-4 is a snapshot, and a score just past a cut-off is worth repeating before it is worth worrying about.
It looks for scarring, not fat or inflammation
A liver can be substantially fatty, or inflamed, with a FIB-4 well under 1.30. The score is built to notice the late structural change, so a low result rules out advanced scarring and says nothing at all about the earlier stages that lead there.
One reading, or the trend
FIB-4 estimates. Repeat panels show.
An Ahead Health membership is a year of structured prevention: repeat blood panels covering liver enzymes, platelets, metabolic and inflammatory markers, a personal report you can actually read, and a prevention team that goes through it with you. It answers the question FIB-4 raises but cannot settle, which is where your own numbers are heading.
A membership is prevention, not treatment. It does not replace care from your own doctor.
- Up to four blood check-ups a year, 80 plus biomarkers each
- Liver enzymes and platelets tracked over time, not measured once
- GGT, metabolic and inflammatory markers, which FIB-4 does not read
- A personal report and an action plan reviewed by Swiss physicians
- A prevention team you can ask about your result
Frequently asked questions
Other calculators
Free tools that ask a different question about the same body.
- BMI calculatorYour weight in relation to your height, and the range that counts as healthy at that height.
- BMR calculatorThe calories your body burns at rest, and the daily total once your activity is added on top.
- SCORE2 calculatorYour 10-year risk of a heart attack or stroke, on the European Society of Cardiology model calibrated for Switzerland.
- sMAF-5 calculatorYour risk of liver fibrosis, from your BMI, sex, diabetes status, one liver enzyme and your platelet count. No waist measurement needed.
- MAFLD calculatorWhether you meet the metabolic fatty liver criteria, from your waist, BMI, triglycerides and GGT, on the 2020 definition.
Source
Sterling RK and colleagues, Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection, Hepatology 2006, volume 43, pages 1317 to 1325. The age-adjusted lower cut-off of 2.00 from 65 follows McPherson S and colleagues, Age as a confounding factor for the accurate non-invasive diagnosis of advanced NAFLD fibrosis, American Journal of Gastroenterology 2017, volume 112, pages 740 to 751.
This calculator provides general health information and is not a medical diagnosis. It does not replace an assessment by a doctor. If your result worries you, or if you have symptoms, speak to a physician.