FIB-4 Calculator
FIB-4 (Fibrosis-4) is a validated screening score that estimates the likelihood of significant liver fibrosis using four routine values: age, AST, ALT, and platelet count. It was developed to help decide who needs further liver evaluation — no biopsy, no imaging, just numbers already on a standard blood panel.
Score validated in adults 35–65; see FAQ if you're outside that range
From the same draw as ALT
Same as K/µL on a US CBC report
Enter your values above to see your results.
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How it works
The formula
FIB-4 = (age × AST) ÷ (platelet count × √ALT). Age in years, AST and ALT in U/L, platelets in 10⁹/L (the same number as K/µL on US lab reports). Example: age 52, AST 34, ALT 40, platelets 220 → (52 × 34) ÷ (220 × 6.32) ≈ 1.27.
Age changes the cutoffs
Because age is in the numerator, FIB-4 drifts upward as you get older even with identical labs. For adults 65 and over, several references suggest using 2.0 (instead of 1.45) as the rule-out cutoff to avoid false positives. At the other end, the score was not validated in adults under 35 — a result in that age group carries more uncertainty.
Where the score comes from
FIB-4 was developed in 2006 in an HIV/HCV cohort and has since been validated most strongly in viral hepatitis and NAFLD/MASLD populations. It is a screening tool designed to identify who is unlikely to have advanced fibrosis — its strength is ruling out, not ruling in.
Evidence level & limitations
The 1.45 / 3.25 cutoffs are validated conventions from peer-reviewed cohorts, not official guideline grades for every population. Acute illness, recent intense exercise, and low platelets from non-liver causes can all skew the inputs. FIB-4 is a screening signal, not a diagnosis — abnormal results deserve a practitioner's workup.
Frequently asked questions
How do I calculate my FIB-4 score?
Multiply your age by your AST, then divide by (platelet count × square root of ALT) — all four values from the same blood draw. The calculator above does it instantly and shows which risk band the result falls in.
What is a good FIB-4 score?
Below 1.45 is the standard rule-out zone — in validation studies, scores there made advanced fibrosis unlikely. Between 1.45 and 3.25 is indeterminate (neither reassuring nor alarming on its own), and above 3.25 is a higher-risk signal that warrants a medical workup. For adults 65+, a 2.0 lower cutoff is often suggested.
My score is in the indeterminate zone — what now?
That's the zone where the score genuinely can't say much. In clinical pathways, indeterminate results typically lead to a next step such as elastography (a painless ultrasound-based stiffness measurement) or a specialist conversation — not to a conclusion on their own.
Does FIB-4 work if I'm under 35 or over 65?
With caveats. The score wasn't validated in adults under 35, so results there carry more uncertainty. Over 65, age pushes the score upward and raises false positives — which is why a 2.0 rule-out cutoff is often used for that group instead of 1.45.
Where do I find the four values on my lab report?
AST and ALT are on a standard liver or metabolic panel (sometimes labeled SGOT and SGPT), and platelets are on a CBC. All three are routine — if you've had a general blood draw in the past year, you likely already have everything the score needs.
Is a high FIB-4 score the same as a cirrhosis diagnosis?
No. FIB-4 is a screening score built to flag who might benefit from further evaluation — it does not diagnose cirrhosis or any other condition. A score above 3.25 is a reason to talk to a clinician, not a conclusion.
Sources
- Sterling RK et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology, 2006.
- Vallet-Pichard A et al. FIB-4: an inexpensive and accurate marker of fibrosis in HCV infection. Hepatology, 2007.
- McPherson S et al. Age-adjusted cutoffs for FIB-4 in NAFLD populations — rule-out threshold considerations in adults over 65.
This calculator is for informational purposes only and is not medical advice, diagnosis, or treatment. Reference ranges are general population guidelines — always discuss your lab results with a qualified healthcare professional.