FIB-4 calculator (liver fibrosis index)
A score worked out from your age, AST, ALT and platelet count. It helps estimate the chance of advanced scarring (fibrosis) in the liver. Type your results in the units on your report and it works out FIB-4 as you type, in your browser.
AI-verified against cited sources. Awaiting expert reviewLast reviewed 2026-10-03Liver
Type your results above, or fill in the example, to see FIB-4.
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Educational information, not medical advice. Blood Test Tracker doesn’t diagnose or treat, and it doesn’t replace your clinician. Talk with your clinician before changing medications, supplements or care.
How it’s worked out
The formula
FIB-4 = (age in years × AST in U/L) ÷ (platelet count in 10^9/L × √(ALT in U/L)). Platelets in 10^9/L are the same number as ×10³/µL (K/µL). Age is a fourth input and is not a blood marker.
A worked example
Example numbers, not anyone’s real results, run through the same code as the calculator above.
| Age | 55 years |
|---|---|
| AST | 40 U/L |
| ALT | 36 U/L |
| Platelets | 200 ×10³/µL |
| FIB-4 | 1.83 index |
For an adult aged 55, this result is above the usual range.
What FIB-4 tells you
FIB-4 is not a blood test on its own. It is a calculation that combines your age with three routine results: AST, ALT and platelet count. It helps estimate how likely it is that the liver has advanced scarring, called fibrosis. Scarring builds up slowly and often causes no symptoms. Some labs print the score with your liver tests, and clinicians can also work it out themselves.
Fatty liver disease is common, and many people with it do not develop serious scarring. FIB-4 is a simple, low-cost way to sort people into lower and higher chances of advanced fibrosis, using tests you may already have. A low score points to a lower chance, so many people can be followed in primary care. A higher score is a reason for a closer look with another test, not a result by itself.
Read the full page on FIB-4, with what a high or low result can mean.
Usual ranges
The ranges the result above is placed on. Your own lab’s printed range comes first if it gives one.
- 18–64up to 1.3 index
Sources: Hepatology (AASLD), Clinical Gastroenterology and Hepatology
- 65+up to 2 index
Sources: American Journal of Gastroenterology, Hepatology (AASLD)
Sources
The equation
- Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection, Hepatology (2006)
4 more sources for the ranges and the explanation
- AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease, Hepatology (AASLD) (2023)
- Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease, Clinical Gastroenterology and Hepatology (2009)
- Age as a Confounding Factor for the Accurate Non-Invasive Diagnosis of Advanced NAFLD Fibrosis, American Journal of Gastroenterology (2017)
- LOINC 98488-0 (NLM Clinical Tables), National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. The calculator is version 1.0.0 of our code for this equation, tested against published examples. How we build and check these pages.