FIB-4 Index Calculator

Reviewed by the CalculatorHub team, edited by James Graham. FIB-4 index from age, AST, ALT, and platelet count. Last verified 19 June 2026.

The FIB-4 index is a non-invasive score that combines age, two liver enzymes (AST and ALT), and the platelet count to estimate the likelihood of advanced liver fibrosis. It is used as a first-line screen to decide who needs further assessment. This tool computes the index from your entered values; the cut-offs and what they mean are clinical and depend on the underlying liver condition.

Age (years)

AST (U/L)

ALT (U/L)

Platelet count (10^9/L)

FIB-4 index

0.00

FIB-4 formula

FIB-4 = (age * AST) / (platelet count * sqrt(ALT))

Age is in years, AST and ALT in units per litre (U/L), and platelet count in 10^9 per litre (equivalently 1,000 per microlitre). The ALT is under a square root. The result is a unitless index.

Worked example

For age 50, AST 40 U/L, ALT 30 U/L, and platelets 200 (10^9/L): FIB-4 = (50 * 40) / (200 * sqrt(30)) = 2000 / (200 * 5.4772) = 2000 / 1095.45 = 1.83. Commonly cited cut-offs are below 1.3 (low risk) and above 2.67 (high risk) in some settings, but thresholds vary by disease and age.

Frequently asked questions

What do the FIB-4 cut-offs mean?

In many studies a FIB-4 below about 1.3 makes advanced fibrosis unlikely and a value above about 2.67 makes it more likely, with an indeterminate range between. Thresholds differ by liver disease and are higher in older adults. This tool does not apply cut-offs; it reports the index.

Which AST and ALT units does it use?

Units per litre (U/L), the standard reporting unit on most laboratory panels. Enter the values exactly as reported.

Does FIB-4 replace a liver biopsy?

No. It is a screening estimate that helps decide who needs further tests such as elastography or, rarely, biopsy. It does not diagnose fibrosis on its own.

Is this medical advice?

No. It performs the FIB-4 arithmetic on values you enter. Interpretation and any decisions are for a qualified clinician.

Sources

U.S. Department of Veterans Affairs, hepatitis C resources: VA Viral Hepatitis.
U.S. National Library of Medicine, StatPearls: Liver Fibrosis overview.

Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. Educational tool, not medical advice. See our methodology.