FIB-4 Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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Liver and GI risk tools often combine familiar labs in ways that are not intuitive at a glance. FIB-4 Calculator makes that relationship explicit and returns the exact index or score implemented in this calculator.

What this calculator does

FIB-4 Calculator uses Patient age, AST, ALT, and Platelet count to produce the fib-4 index used by this calculator. It only uses the fields shown in this calculator; it does not silently add tests, diagnoses, symptoms, or clinical variables that are absent from the interface. Uses standard health-calculator relationships where a stable equation exists; complex or policy-dependent tools expose assumptions/points so the result can be checked against the current clinical or public-health source.

How to use it

Enter or select Patient age, AST, ALT, and Platelet count. Keep laboratory units consistent and use values from the clinical time point required by the named model. If an input is unknown, it is better to leave the calculation unresolved than to invent a value.

How the calculation works

FIB-4 = age × AST ÷ [platelet count × square root of ALT]. Age is in years, AST/ALT in U/L, and platelets in ×10^9/L.

Example

Using the calculator’s prefilled demonstration values, the primary output is 1.98, labeled “FIB-4 index”; Age is 35 and Platelets is 150 ×10⁹/L. That sample is useful for checking the calculation path, but real interpretation should use verified measurements from the same clinical or study context.

How to interpret the result

FIB-4 is most useful for fibrosis risk stratification. In MASLD pathways, lower values can help rule out advanced fibrosis in appropriate populations, while indeterminate/higher results usually lead to a second noninvasive test rather than a diagnosis from FIB-4 alone.

Limitations and notes

Cutoffs can differ by disease population and guideline, and lab values can change quickly with treatment or acute illness. Use trends, the correct indication, and confirmatory testing or specialist assessment when the result could change management.