FIB-4 Index Calculator

About this calculator

The FIB-4 index is a widely used non-invasive screening score for liver fibrosis (scarring), calculated from four routinely available values: age, AST (aspartate aminotransferase), ALT (alanine aminotransferase), and platelet count. The formula — Age × AST / (Platelets × √ALT) — combines rising liver enzymes and falling platelet counts, both markers that tend to worsen as fibrosis progresses, into a single number.

FIB-4 is used by hepatologists, gastroenterologists, and primary care physicians as a first-line triage tool, particularly for patients with chronic liver conditions like hepatitis B/C or non-alcoholic fatty liver disease (NAFLD): a low score helps rule out advanced fibrosis without a biopsy, while a high score flags patients who need further imaging or specialist referral. It's a screening estimate, not a diagnosis, and is always interpreted alongside a patient's full clinical picture.