Fib-4 Calculator — Liver Fibrosis Risk Score

Calculate the FIB-4 index from age, AST, ALT, and platelet count. Includes the age-adjusted low-risk cutoff for patients 65 and older.

July 2, 2026

Age (years)

Platelets (×10⁹/L)

AST (U/L)

ALT (U/L)

Low risk of advanced fibrosis

FIB-4 = 1.24

FIB-4 = (Age × AST) ÷ (Platelets × √ALT). This is a non-invasive fibrosis risk screening estimate, not a diagnosis — FIB-4 performs best at ruling advanced fibrosis out (negative predictive value over 90% at low scores) rather than confirming it. Indeterminate or high results are typically followed up with elastography (FibroScan) or specialist evaluation, not treated as a final answer on their own.

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Reference Values

Last verified: Jul 2, 2026

Category	Range	What It Means	Status
Low Risk ★	Below 1.30 (below 2.00 if age ≥65)	Low probability of advanced (F3–F4) liver fibrosis. Negative predictive value exceeds 90% — FIB-4 is best at ruling fibrosis out, not confirming it. Routine monitoring is typically sufficient.	★ Best
Indeterminate	1.30 – 2.67	Cannot reliably rule advanced fibrosis in or out from FIB-4 alone. Further non-invasive testing (elastography/FibroScan) or specialist referral is typically recommended.	Okay
High Risk	Above 2.67	High probability of advanced fibrosis. Specificity around 97% at the higher original Sterling cutoff of 3.25 — hepatology referral and further staging is typically warranted.	Poor

Source: Sterling RK et al. (2006) Hepatology — original FIB-4 validation study (1.45/3.25 cutoffs); subsequent studies established the more commonly used 1.30/2.67 cutoffs and the age-adjusted <2.0 low-risk threshold for patients 65 and older

Worked Examples

Age 45, AST 30, ALT 25, Platelets 250

Age: 45
AST: 30 U/L
ALT: 25 U/L
Platelets: 250 ×10⁹/L

FIB-4 = 1.08 (Low risk)

(45 × 30) / (250 × √25) = 1350 / 1250 = 1.08. Below the 1.30 low-risk cutoff — advanced fibrosis is unlikely.

Age 50, AST 45, ALT 50, Platelets 200

Age: 50
AST: 45 U/L
ALT: 50 U/L
Platelets: 200 ×10⁹/L

FIB-4 = 1.59 (Indeterminate)

(50 × 45) / (200 × √50) = 2250 / 1414.2 = 1.59. Falls in the indeterminate zone (1.30–2.67) — further testing such as elastography is typically recommended.

Age 55, AST 65, ALT 40, Platelets 180

Age: 55
AST: 65 U/L
ALT: 40 U/L
Platelets: 180 ×10⁹/L

FIB-4 = 3.14 (High risk)

(55 × 65) / (180 × √40) = 3575 / 1138.4 = 3.14. Above the 2.67 high-risk cutoff — specialist referral for advanced fibrosis evaluation is typically warranted.

Age 70 (Age-Adjusted Cutoff Matters), AST 38, ALT 42, Platelets 210

Age: 70
AST: 38 U/L
ALT: 42 U/L
Platelets: 210 ×10⁹/L

FIB-4 = 1.95 — Indeterminate by standard cutoff, Low risk by age-adjusted cutoff

(70 × 38) / (210 × √42) = 2660 / 1360.9 = 1.95. Using the standard <1.30 low-risk cutoff, this looks indeterminate. But for patients 65 and older, the recommended low-risk cutoff rises to <2.00 to offset age-related score inflation — under that adjusted cutoff, this result is low risk.

How to Use This Calculator

1

Enter age

Age in years — this directly affects the score and which low-risk cutoff applies.
2

Enter platelet count

Platelet count in ×10⁹/L (the standard unit on most complete blood count reports, sometimes shown as 10³/µL — same value).
3

Enter AST and ALT

Both liver enzymes in U/L from a standard liver function panel.
4

Read the FIB-4 score and risk category

Results show the calculated FIB-4 value, risk category (low/indeterminate/high), and flag when the age-adjusted cutoff for patients 65+ applies.

What Each Value Means

FIB-4 Score (index (unitless)): A composite index combining age, AST, ALT, and platelet count to estimate the likelihood of advanced (F3–F4) liver fibrosis without requiring a biopsy. Higher scores indicate greater estimated fibrosis risk.
AST (Aspartate Aminotransferase) (U/L): A liver enzyme that rises with liver cell damage. Used in the numerator of the FIB-4 formula — higher AST relative to the other inputs increases the score.
ALT (Alanine Aminotransferase) (U/L): A liver-specific enzyme used in the denominator of the FIB-4 formula (as its square root) — higher ALT relative to the other inputs decreases the score.
Platelet Count (×10⁹/L): Platelets often decline as liver fibrosis progresses (due to portal hypertension and splenic sequestration), so lower platelet counts increase the FIB-4 score.

Frequently Asked Questions

What is the FIB-4 formula?

FIB-4 = (Age in years × AST in U/L) ÷ (Platelet count in ×10⁹/L × √ALT in U/L). All four values come from a standard complete blood count and liver panel — no additional testing is required beyond routine labs.

What FIB-4 score indicates a high risk of liver fibrosis?

The most commonly used cutoffs are: below 1.30 = low risk of advanced fibrosis, 1.30–2.67 = indeterminate, and above 2.67 = high risk of advanced fibrosis. The original Sterling et al. (2006) validation study used slightly different cutoffs (1.45 and 3.25), which some clinicians still reference — both cutoff sets are in clinical use.

Why does FIB-4 use a different low-risk cutoff for patients over 65?

FIB-4 scores naturally trend higher with age even without additional fibrosis, since age is a direct multiplier in the formula. This inflates false-positive rates in older patients when using the standard 1.30 cutoff. Guidelines recommend using a higher low-risk cutoff of below 2.00 for patients 65 and older to correct for this age-related score inflation.

How accurate is FIB-4 at detecting liver fibrosis?

FIB-4 performs best at ruling advanced fibrosis out, not confirming it — a low score has a negative predictive value exceeding 90%, meaning it's quite reliable for excluding significant fibrosis. High scores are less definitive: even at the stricter 3.25 cutoff, positive predictive value is only around 65%. Indeterminate and high scores are typically followed up with imaging-based elastography (FibroScan) or specialist evaluation rather than treated as a final diagnosis.

What conditions is FIB-4 used to screen for?

FIB-4 was originally validated in patients with hepatitis C and HIV/HCV coinfection, and is now widely used as a first-line, low-cost screening tool for advanced fibrosis in non-alcoholic fatty liver disease (NAFLD/NASH), chronic hepatitis B and C, and general liver disease risk stratification in primary care, since it only requires routine labs already available in most patients.