Free tool

FIB-4 Liver Fibrosis Score Calculator

Q: Which blood tests give me the FIB-4 inputs?

AST and ALT are on a hepatic function panel and on a comprehensive metabolic panel; the platelet count is on any CBC. Age is the fourth input. No specialty test is needed, which is why guidelines recommend FIB-4 as the first step.

Q: What does an indeterminate FIB-4 mean?

Between 1.3 and 2.67 the score can neither rule advanced fibrosis in nor out. The AASLD pathway is a second-line test — liver stiffness by vibration-controlled elastography (FibroScan) or an ELF blood test — rather than a repeat FIB-4.

Q: Why does the cut point change at 65?

Age is in the numerator, so FIB-4 climbs with age even when the liver is fine. Using 1.3 in older adults sends too many people for further testing; McPherson and colleagues showed 2.0 preserves accuracy at 65 and over.

Q: Does a low FIB-4 mean I do not have fatty liver?

No. FIB-4 estimates scarring (fibrosis), not fat or inflammation. A low score in someone with fatty liver means advanced fibrosis is unlikely today; the guidance is to repeat it every one to three years while risk factors persist.

The short answer

Enter your age, AST, ALT and platelet count and the calculator returns the FIB-4 index — the non-invasive score guidelines use to sort people with fatty liver or viral hepatitis into low, indeterminate and high risk of advanced fibrosis. Below 1.3 (2.0 at 65 and over) is low risk; above 2.67 is high risk and calls for elastography or specialist review.

Inputs: Age · AST · ALT · platelets
Low risk: < 1.3 (< 2.0 at 65+)
High risk: > 2.67
Cost: Free

Age

years

AST

U/L

AST range

ALT

U/L

ALT range

Platelets

K/µL

K/µL = ×10⁹/L · Platelet Count range

Enter your values to calculate.

FIB-4 = (age × AST) ÷ (platelets [10⁹/L] × √ALT)

Educational — a derived index, not a diagnosis. Nothing you enter leaves your browser.

How the FIB-4 index is calculated

FIB-4 = (age × AST) ÷ (platelets [10⁹/L] × √ALT)

Worked example

Age (years)	AST (U/L)	ALT (U/L)	Platelets (K/µL)	FIB-4 index
52	34	41	230	1.20

Falls in: Low risk of advanced fibrosis.

How to read the result

Standard cut points

FIB-4 index	Reads as	What it usually means
< 1.3	Low risk of advanced fibrosis	Below 1.3, advanced fibrosis is unlikely (high negative predictive value); guidance is to repeat the score every 1–3 years if metabolic risk factors persist.
1.3 – 2.67	Indeterminate	The score cannot rule advanced fibrosis in or out. Guidance suggests a second-line test — liver stiffness by elastography (FibroScan) or an ELF test — before any conclusion.
≥ 2.67	High risk of advanced fibrosis	Scores above 2.67 are associated with advanced fibrosis and merit specialist evaluation. FIB-4 is a screening score, not a biopsy; imaging or elastography follows.

Age 65 and over

FIB-4 index	Reads as	What it usually means
< 2	Low risk of advanced fibrosis (age ≥ 65 cut point)	Because age sits in the numerator, FIB-4 drifts upward with age alone. At 65 and older the low-risk cut point is raised to 2.0; below it advanced fibrosis is unlikely.
2 – 2.67	Indeterminate	At 65 and older, 2.0–2.67 is the indeterminate zone. A second-line test (elastography or ELF) resolves it.
≥ 2.67	High risk of advanced fibrosis	Above 2.67 remains the high-risk cut point regardless of age; specialist evaluation is the next step.

Cut points reviewed by Youmna DiStefano, MD on 2026-09-26. Sources below.

Limits

Validated for adults roughly 35–65 with suspected fatty liver disease or viral hepatitis; it is less reliable under 35 (false lows) and needs the higher 2.0 cut point at 65 and over. Acute hepatitis, alcohol excess, muscle injury (AST) and low platelets from other causes all distort it. It estimates fibrosis risk, not fat content or inflammation.

Sources

Sterling RK, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology 2006;43:1317–1325. doi.org/10.1002/hep.21178
Shah AG, et al. Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol 2009;7:1104–1112. doi.org/10.1016/j.cgh.2009.05.033
Rinella ME, et al. AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease. Hepatology 2023;77:1797–1835. doi.org/10.1097/HEP.0000000000000323
McPherson S, et al. Age as a Confounding Factor for the Accurate Non-Invasive Diagnosis of Advanced NAFLD Fibrosis. Am J Gastroenterol 2017;112:740–751. doi.org/10.1038/ajg.2016.453

Frequently asked questions

Which blood tests give me the FIB-4 inputs?

AST and ALT are on a hepatic function panel and on a comprehensive metabolic panel; the platelet count is on any CBC. Age is the fourth input. No specialty test is needed, which is why guidelines recommend FIB-4 as the first step.

What does an indeterminate FIB-4 mean?

Between 1.3 and 2.67 the score can neither rule advanced fibrosis in nor out. The AASLD pathway is a second-line test — liver stiffness by vibration-controlled elastography (FibroScan) or an ELF blood test — rather than a repeat FIB-4.

Why does the cut point change at 65?

Age is in the numerator, so FIB-4 climbs with age even when the liver is fine. Using 1.3 in older adults sends too many people for further testing; McPherson and colleagues showed 2.0 preserves accuracy at 65 and over.

Does a low FIB-4 mean I do not have fatty liver?

No. FIB-4 estimates scarring (fibrosis), not fat or inflammation. A low score in someone with fatty liver means advanced fibrosis is unlikely today; the guidance is to repeat it every one to three years while risk factors persist.

Which biomarkers does this tool cover?

Which tests give you these numbers?

Physician-authorized, drawn at Quest, Labcorp or BioReference. Results in 1–3 business days for most tests.