Introduction
The FIB-4 Calculator is a free tool that helps estimate liver scarring, also called fibrosis. It uses four simple numbers: your age, your AST level, your ALT level, and your platelet count. You can get all of these from a normal blood test.
Liver scarring often has no signs early on. The FIB-4 index gives doctors a quick, low-cost way to spot people who may have advanced fibrosis. It is often used for fatty liver disease (NAFLD/MASLD), hepatitis C, and other long-term liver problems.
Your score falls into one of three zones. A low score means bad scarring is unlikely. A middle score means more tests may be needed. A high score means scarring or cirrhosis may be present. This tool shows your score, the zone you are in, and the full math behind it, step by step.
You can pick between two sets of cutoffs: the NAFLD/general set or the original hepatitis C study set from Sterling et al. (2006). The calculator also shows how your score would be read under the other set.
The FIB-4 index is a screening tool, not a diagnosis. It works best for people between 35 and 65 years old.5 Above 65 the usual low cut-off is raised, to a FIB-4 of 2.0.2 Always talk with a doctor about your results. If your score points to advanced disease, your care team may also look at scores like the MELD Calculator or the Child Pugh Calculator.
How to use our FIB-4 Calculator
Enter your age and three blood test results: AST, ALT, and platelet count. The FIB-4 calculator gives you a FIB-4 score, tells you your risk zone for liver fibrosis, and shows the math step by step.
Threshold Set: Pick which cutoffs to use. Choose "NAFLD / General" for most patients, or "Original HCV Study" for hepatitis C. The original cutoffs come from a study of people with both HIV and hepatitis C. The score stays the same, but the risk zones change.
Age: Type your age in years. The tool warns you if you are under 35 or over 65, since FIB-4 is less accurate at those ages.5
AST: Type your aspartate aminotransferase level in U/L from your blood test. A typical reference range is 8 to 33 U/L.4
ALT: Type your alanine aminotransferase level in U/L. Use the plain number from your lab report. The calculator computes the square root.
Platelet Count: Type your platelet count and pick the unit: × 10⁹/L or × 10³/µL. Both units use the same number, so the score does not change.
Press Calculate to see your FIB-4 score, risk zone, chart, and full solution. Press Reset to start over with the sample values.
What Is the FIB-4 Index?
The FIB-4 index is a simple blood test score that estimates how much scarring (fibrosis) a person may have in their liver. Doctors use it as a first check before ordering more tests. It does not need a needle biopsy. It only needs a patient's age and three lab values that most people already get in routine blood work.
What Goes Into the Score
- Age – in years. Liver scarring gets more common as people get older.
- AST – aspartate aminotransferase, a liver enzyme measured in U/L.
- ALT – alanine aminotransferase, another liver enzyme in U/L.
- Platelet count – measured as ×10⁹/L or ×10³/µL. Both units use the same number. Platelets often drop when the liver is badly scarred.
The FIB-4 formula is: (Age × AST) ÷ (Platelets × √ALT).1 A higher score points to more possible scarring.
What the FIB-4 Score Means
Two sets of cutoffs are common. For fatty liver disease (NAFLD/MASLD) and general use, a score under 1.30 means advanced fibrosis is unlikely, 1.30 to 2.67 is unclear, and over 2.67 suggests advanced fibrosis or cirrhosis may be present.2 The original study by Sterling and colleagues, done in patients with hepatitis C and HIV, used 1.45 and 3.25 instead.1 A low score is very good at ruling scarring out. In 145 biopsy-proven fatty liver patients, a FIB-4 under 1.30 carried a negative predictive value of 95% and would have spared 62% of them a liver biopsy.3 A high score is a warning sign that needs follow-up, such as elastography (FibroScan), imaging, or a liver biopsy.
Who Uses FIB-4
Primary care doctors, liver specialists (hepatologists), and diabetes doctors use FIB-4 to screen people at risk of liver disease. That includes people with fatty liver, type 2 diabetes, obesity, hepatitis B or C, or heavy alcohol use. It helps decide who needs to see a specialist and who can simply be watched over time.
Limits to Keep in Mind
FIB-4 is an estimate, not a diagnosis. It is less accurate in people under 35, where it can miss real disease, and in people over 65, where it can flag scarring that is not there.5 Other things can also shift the score, such as mono, alcohol use, blood disorders that lower platelets, or medicines that raise liver enzymes. Always read the score together with a full clinical picture, and repeat testing over time to watch for change. Lifestyle change is the main treatment for fatty liver.