FIB-4 Calculator

The FIB-4 index (Fibrosis-4) is a score built from four routine numbers: your age, two liver enzymes called AST and ALT, and your platelet count. Doctors use it as a quick first check for advanced scarring of the liver. It needs no extra test, because the numbers usually come from blood work you have already had.

What FIB-4 Measures

Fibrosis is scar tissue that builds up in the liver after long-term damage. It is graded from F0 (no scarring) to F4 (cirrhosis), and advanced fibrosis means stage F3 (bridging fibrosis) or F4⁴. FIB-4 does not see scar tissue directly. It estimates how likely advanced fibrosis is. The enzymes reflect stress on liver cells, and the platelet count reflects changes in the spleen that come with scarring⁵. FIB-4 does not measure liver fat, and it cannot tell what is causing a liver problem.

The Formula

FIB-4 = (Age x AST) / (Platelets x √ALT)

Age in years, AST and ALT in U/L, platelets in 10^9/L

The score was developed by Sterling and colleagues in 2006 in people with HIV and hepatitis C¹.

How This Calculator Computes Your Result

Enter your age and the AST, ALT and platelet count from the same blood test. Older reports may call AST "SGOT" and ALT "SGPT". AST and ALT can be entered in U/L (the same number as IU/L) or in µkat/L, which the tool multiplies by 60. Platelets reported as 10^9/L, 10^3/µL, K/µL or 10^3/mm3 are all the same number, for example 250. If your report shows the full count, such as 250,000 per µL, the tool divides by 1,000. The score is rounded to two decimals, and the band is set from that rounded number. From age 65, the tool raises the low-risk cutoff to 2.00. It adds a note if you are 35 or younger, if your platelets are outside the usual 150 to 400⁷, or if AST or ALT is above 200 U/L. If your lab already printed a FIB-4 score, ours may differ by 0.01 because of rounding.

What Your Result Means

These bands come from the US (AASLD) and European (EASL-EASD-EASO) guidance on fatty liver disease⁴ ⁵.

The 1.30 and 2.67 cutoffs come from a study of 541 adults with fatty liver disease. In that group, 90% of people at or below 1.30 did not have advanced fibrosis, and 80% of people at or above 2.67 did². The middle band is often called the indeterminate zone. The 2.00 cutoff for older adults is explained below³. You may also see 1.45 and 3.25 on some reports and websites. Those are the original cutoffs, set in people with HIV and hepatitis C¹.

How FIB-4 Is Used After a Blood Test

The American Association for the Study of Liver Diseases (AASLD) advises a FIB-4 check for adults with type 2 diabetes, prediabetes, two or more metabolic risk factors, or fat seen on a liver scan, repeated every 1 to 2 years⁴. The European guideline also uses FIB-4 as the first of two steps⁵. A score of 1.30 or more usually leads to a second test. This is often elastography, a quick scan that measures liver stiffness (vibration-controlled transient elastography, often called FibroScan), or the ELF blood test⁴. FIB-4 used alone can give many false alarms, which is why the second step exists⁵.

Older research and some lab reports say NAFLD (nonalcoholic fatty liver disease). In 2023, liver societies renamed it metabolic dysfunction-associated steatotic liver disease (MASLD), which requires at least one of five cardiometabolic risk factors⁶. The FIB-4 cutoffs did not change with the new name⁵.

When FIB-4 Can Be Misleading

Age is part of the formula, so the score rises as you get older even if your liver does not change. In a study of 634 adults with biopsy-confirmed fatty liver disease, about 2 in 3 people aged 65 and over who did not have advanced fibrosis still scored above 1.30. With a cutoff of 2.0, that fell to about 3 in 10 people³. The same study found FIB-4 worked poorly at age 35 and under³. At younger ages, a small age number pulls the score down, so a low result is less reassuring.

Anything that changes AST, ALT or platelets for another reason moves the score too. A 2024 clinical review lists acute inflammation of the liver among the limits of these tests⁸. Hard exercise counts: after one hour of weightlifting, AST and ALT stayed raised for at least 7 days in healthy men who were new to it⁹. For example, a 45-year-old with AST 25, ALT 25 and platelets 250 scores 0.90, but with AST 75 and ALT 40 the same person scores 2.13. Platelet counts can also be low or high for reasons unrelated to the liver, such as bone marrow problems, iron deficiency or a recent infection⁷. Low platelets push FIB-4 up, and high platelets pull it down.