FIB-4 Liver Fibrosis Calculator

About this calculator

The FIB-4 index is a non-invasive liver fibrosis screening score calculated from four routine values: FIB-4 = (Age × AST) / (Platelet count × √ALT). It was originally validated in hepatitis C/HIV co-infected patients but is now widely used across chronic liver disease, especially non-alcoholic fatty liver disease (NAFLD/NASH), to flag patients likely to have advanced fibrosis without needing a liver biopsy.

The standard cutoffs are age-adjusted because AST and platelet levels naturally shift with age: for patients under 65, a score below 1.45 suggests low risk of advanced fibrosis and above 3.25 suggests high risk, while patients 65 and older use a higher low-risk cutoff (below 2.0) since scores tend to run higher in that age group regardless of liver health — primary care doctors and hepatologists use FIB-4 as a first-line triage tool to decide who needs referral for further liver workup.

This calculator takes age, AST, ALT and platelet count and returns the FIB-4 score along with the age-adjusted fibrosis risk category.