FIB-4 Calculator — Liver Fibrosis Index
The FIB-4 index combines age, AST, ALT, and platelet count into a single score used to screen for advanced liver fibrosis without a biopsy. Enter your lab values to get the score and its risk category.
years
U/L
U/L
10⁹/L
Indeterminate (F1–F3)
- 1
Numerator: Age × AST
45 × 40 = 1,800 - 2
√ALT
√35 = 5.916 - 3
Denominator: Platelets × √ALT
200 × 5.916 = 1,183.22 - 4
FIB-4 score
1,800 ÷ 1,183.22 = 1.52
How does this calculator work?
FIB-4 = (Age × AST) / (Platelets × √ALT). A score below 1.30 suggests low risk of advanced fibrosis; above 2.67 suggests high risk. The indeterminate zone (1.30–2.67) requires further evaluation. This is a screening index — not a diagnosis — and must be interpreted by a clinician.
Formula
How this is calculated
FIB-4 (Fibrosis-4) is a non-invasive biomarker panel first validated by Sterling et al. (2006) in patients with HIV/HCV co-infection, and subsequently applied broadly in chronic liver disease including NAFLD/MASLD and HBV. The formula divides the product of age and AST by the product of platelet count and the square root of ALT: FIB-4 = (Age × AST) / (Platelets × √ALT). Platelets are entered in 10⁹/L (the same scale as "×10³/µL" reported on most blood panels); AST and ALT are in international units per litre (U/L).
The original cut-offs from Sterling et al. are < 1.30 (low risk for advanced fibrosis, METAVIR F0–F1; negative predictive value ~90%) and > 2.67 (high risk for significant fibrosis, F3–F4; positive predictive value ~82%). Scores between 1.30 and 2.67 are indeterminate and typically require further evaluation such as liver stiffness measurement (elastography) or biopsy. Some guidelines for MASLD use slightly different cut-offs (< 1.30 rules out advanced fibrosis; > 2.67 identifies high-risk patients needing specialist referral).
FIB-4 is a screening tool, not a diagnosis. Results must be interpreted alongside clinical history, other biomarkers, imaging, and specialist judgement. Acute liver injury, haematological conditions, or recent strenuous exercise can distort individual components and make the score unreliable.
Frequently asked questions
Enter platelets as ×10⁹/L, which is the same numerical value as ×10³/µL or ×10³/mm³ — the three notations all represent the same thing. A typical normal platelet count is 150–400 × 10⁹/L. Do not enter raw values from a "10³/µL" report without checking the scale.
FIB-4 was originally validated for HCV; its accuracy is well-documented for NAFLD/MASLD and HBV, but less so for rarer liver conditions. It can be falsely elevated in people over 65 years or in those with conditions that lower platelets (e.g. cirrhosis, immune thrombocytopenia). Always use it as part of a broader clinical workup.
No — a score above 2.67 indicates a higher statistical probability of significant fibrosis (F3–F4) based on population data, but it is not diagnostic. Liver biopsy remains the gold standard for staging fibrosis. Elastography (FibroScan) is a widely used non-invasive alternative that may be ordered before biopsy.
Also known as
TG we-Calculate Editorial Team. (2026). FIB-4 Calculator — Liver Fibrosis Index [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/fib-4-calculator
TG we-Calculate Editorial Team. "FIB-4 Calculator — Liver Fibrosis Index." TG we-Calculate. 2026. https://we-calculate.com/calculator/fib-4-calculator.
TG we-Calculate Editorial Team, "FIB-4 Calculator — Liver Fibrosis Index," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/fib-4-calculator
@misc{wecalculate_fib_4_calculator, title = {FIB-4 Calculator — Liver Fibrosis Index}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/fib-4-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?