NAFLD Fibrosis Score Calculator

NFS range	Tier	Clinical meaning
< -1.455	Low	Predicts absence of advanced (F3-F4) fibrosis — biopsy often avoidable
-1.455 to 0.676	Indeterminate	Cannot reliably classify — consider elastography or biopsy
> 0.676	High	Predicts presence of advanced (F3-F4) fibrosis — further evaluation warranted

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Walk-through

How to Use This Calculator

3 steps

1

Enter age, BMI, and diabetes status

Type the patient's age (years) and BMI (kg/m²). Check the "Impaired fasting glucose or diabetes" box if the patient has impaired fasting glucose or diagnosed diabetes — this adds a fixed 1.13 points to the score.

2

Enter AST, ALT, platelets, and albumin

Enter AST and ALT (any consistent unit, typically U/L — only their ratio is used), platelet count in ×10⁹/L, and albumin in g/dL. All six fields are required; the calculator will not compute a score until every value is a real number greater than zero.

3

Read the score and probability band

The result card shows the NAFLD Fibrosis Score (NFS) and the probability of advanced fibrosis: low (< -1.455), indeterminate (-1.455 to 0.676), or high (> 0.676). Open the Components tab to see how each variable contributed, and the Interpretation tab for the full band table and what to do next for an indeterminate result.

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Reference

Formula & Methodology

2 formulas

NAFLD Fibrosis Score (NFS)

NFS = -1.675 + 0.037×age + 0.094×BMI + 1.13×(IFG/diabetes: yes=1, no=0) + 0.99×(AST/ALT) − 0.013×platelets − 0.66×albumin

A six-variable logistic regression derived and validated by Angulo et al. (2007) in 733 patients with biopsy-proven NAFLD, using age in years, BMI in kg/m², impaired fasting glucose or diabetes (1 if present, 0 if not), the AST/ALT ratio, platelet count in ×10⁹/L, and albumin in g/dL.

Probability bands

NFS < -1.455 → low | -1.455 to 0.676 → indeterminate | NFS > 0.676 → high

Two cutoffs split the score into three zones. Below -1.455 predicts absence of advanced (F3-F4) fibrosis with a negative predictive value around 93%; above 0.676 predicts presence of advanced fibrosis with a positive predictive value around 90%. Scores between the cutoffs are indeterminate and need a second-line test.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Review · Updated 2026-07-22 · 2 sources

Editorial accountability

Author: Quinn Sumner - Editor

Owner: Quinn Sumner - Editorial owner

Reviewer: Calculover Editorial Review - Clinical-source review

Last reviewed: 2026-07-22

Last verified: 2026-07-22

Data effective: 2026-07-22

Methodology

The calculator implements the original NAFLD Fibrosis Score regression (Angulo et al., Hepatology 2007): NFS = -1.675 + 0.037×age + 0.094×BMI + 1.13×(IFG/diabetes) + 0.99×(AST/ALT) − 0.013×platelets − 0.66×albumin. Every coefficient and both probability-band cutoffs (-1.455, 0.676) were cross-verified against the original Hepatology paper and the MDCalc reproduction of the same regression.

Assumption: All six inputs (age, BMI, AST, ALT, platelets, albumin) must be positive, real-world values; the calculator withholds a result rather than compute a spurious score from a missing or zero value.

Assumption: AST and ALT may be entered in any consistent unit since only their ratio is used in the regression.

Assumption: The 'impaired fasting glucose or diabetes' checkbox contributes a fixed 1.13 points regardless of how far outside normal range the glucose value is.

Limitations & guidance

The score was derived and validated specifically in patients with biopsy-confirmed NAFLD and may be less reliable in other causes of liver disease, in younger patients, or in those with a normal BMI.

Scores between -1.455 and 0.676 are indeterminate by design — they cannot reliably classify fibrosis stage and require a second-line test such as elastography or biopsy.

This is a probability estimate, not a fibrosis stage or a diagnosis, and must not be the sole basis of any individual treatment or referral decision.

Professional guidance: This calculator is for education and clinical decision support only and is not medical advice, diagnosis, or treatment. The NAFLD fibrosis score supports, but does not replace, the judgment of a licensed clinician, elastography, or liver biopsy; treatment decisions require full clinical assessment.

Primary sources

The NAFLD fibrosis score: A noninvasive system that identifies liver fibrosis in patients with NAFLD - Angulo P, Hui JM, Marchesini G, et al. Hepatology, 2007;45(4):846-854

NAFLD (Non-Alcoholic Fatty Liver Disease) Fibrosis Score Calculator - MDCalc

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Glossary

Key Terms Explained

7 terms

NAFLD fibrosis score (NFS) A validated regression score (Angulo 2007) that estimates the probability of advanced liver fibrosis in patients with nonalcoholic fatty liver disease from six routine clinical and laboratory variables.

Advanced fibrosis Fibrosis stage F3 (bridging fibrosis) or F4 (cirrhosis) on liver biopsy — the stages most strongly associated with liver-related mortality and the ones this score is designed to flag.

NASH Nonalcoholic steatohepatitis — the more aggressive subtype of NAFLD with active inflammation and hepatocyte injury, which drives fibrosis progression over time.

Regression score A weighted sum of clinical variables, each multiplied by a coefficient derived from a statistical model fit to a validation cohort, used here to estimate fibrosis probability without a biopsy.

Impaired fasting glucose (IFG) A fasting blood glucose between 100 and 125 mg/dL — a pre-diabetic state that, along with diagnosed diabetes, adds 1.13 points to the NAFLD fibrosis score.

BMI Body mass index, weight in kilograms divided by height in meters squared (kg/m²) — used in the score as a proxy for metabolic risk.

Platelet count The number of platelets per unit of blood, in ×10⁹ per liter. Platelet count tends to fall as liver fibrosis and portal hypertension progress, so higher counts subtract points from the score.

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Scenarios

Real-World Examples

3 worked examples

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Low probability

45-year-old, no diabetes

Age / BMI 45 yr / 27 kg/m² IFG / diabetes No AST / ALT 30 / 40 U/L (ratio 0.75) Platelets / Albumin 250 ×10⁹/L / 4.3 g/dL

NFS = -1.675 + 0.037(45) + 0.094(27) + 1.13(0) + 0.99(0.75) − 0.013(250) − 0.66(4.3) = -2.82. This is well below the -1.455 cutoff, predicting absence of advanced (F3-F4) fibrosis — a liver biopsy can often be safely avoided for this result.

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Indeterminate

58-year-old with diabetes

Age / BMI 58 yr / 32 kg/m² IFG / diabetes Yes AST / ALT 45 / 50 U/L (ratio 0.90) Platelets / Albumin 210 ×10⁹/L / 4.0 g/dL

NFS = -1.675 + 0.037(58) + 0.094(32) + 1.13(1) + 0.99(0.90) − 0.013(210) − 0.66(4.0) = 0.13. This falls between the two cutoffs — the indeterminate zone — meaning the score cannot reliably rule advanced fibrosis in or out. A follow-up test such as transient elastography or liver biopsy is the recommended next step.

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High probability

68-year-old with diabetes and obesity

Age / BMI 68 yr / 35 kg/m² IFG / diabetes Yes AST / ALT 70 / 45 U/L (ratio 1.56) Platelets / Albumin 140 ×10⁹/L / 3.3 g/dL

NFS = -1.675 + 0.037(68) + 0.094(35) + 1.13(1) + 0.99(1.556) − 0.013(140) − 0.66(3.3) = 2.80. This is well above the 0.676 cutoff, predicting presence of advanced (F3-F4) fibrosis — further evaluation such as elastography or biopsy is generally warranted.

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Deep Dive

Understanding the NAFLD Fibrosis Score

3 chapters · 4 min read

The NAFLD fibrosis score turns six routine clinical and laboratory values into a single number that estimates the probability of advanced liver fibrosis in patients with nonalcoholic fatty liver disease. Developed by Angulo and colleagues in 2007, it remains one of the most widely used non-invasive tools for deciding which NAFLD patients need a specialist referral, elastography, or biopsy — and which do not.

How the score works

The NAFLD fibrosis score combines age, BMI, impaired fasting glucose or diabetes status, the AST/ALT ratio, platelet count, and albumin into a weighted regression: NFS = -1.675 + 0.037×age + 0.094×BMI + 1.13×(IFG/diabetes) + 0.99×(AST/ALT) − 0.013×platelets − 0.66×albumin.

The direction of each coefficient reflects biology: older age, higher BMI, diabetes, and a rising AST/ALT ratio all push the score up (toward more advanced fibrosis), while higher platelet count and higher albumin — both markers of preserved liver synthetic function and the absence of portal hypertension — pull the score down.

Interpreting the two cutoffs

Two cutoffs, both derived and validated in the original cohort, split the score into three zones. A score below -1.455 predicts the absence of advanced (F3-F4) fibrosis with a negative predictive value near 93% — most of these patients can avoid a biopsy. A score above 0.676 predicts the presence of advanced fibrosis with a positive predictive value near 90%, generally prompting further evaluation.

Scores that fall between the two cutoffs are indeterminate — roughly a quarter to a third of patients in the validation cohort landed here. An indeterminate result is not a calculator failure; it means the six variables alone cannot resolve the question, and a second-line test such as transient elastography (FibroScan) or liver biopsy is the appropriate next step.

Limits and how it is used

The NAFLD fibrosis score was derived and validated specifically in patients with biopsy-confirmed NAFLD — it is not intended for other causes of liver disease (viral hepatitis, alcohol-related liver disease, autoimmune hepatitis) and performance may be less reliable outside that population, in younger patients, or in those with normal BMI. It estimates a probability of advanced fibrosis, not a fibrosis stage, and does not replace a full clinical assessment, elastography, or biopsy when those are indicated. Like the score itself, this calculator is a screening aid, not a diagnostic test.

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Questions

Frequently Asked Questions

6 questions

Where does the NAFLD fibrosis score formula come from?+

It comes from Angulo P, Hui JM, Marchesini G, et al. "The NAFLD fibrosis score: A noninvasive system that identifies liver fibrosis in patients with NAFLD." Hepatology. 2007;45(4):846-854 — a regression derived and validated in 733 patients with biopsy-proven NAFLD, using age, BMI, impaired fasting glucose or diabetes, AST/ALT ratio, platelet count, and albumin.

What does a low NAFLD fibrosis score mean?+

A score below -1.455 predicts the absence of advanced (F3-F4) fibrosis with a negative predictive value around 93%, meaning a liver biopsy can often be safely avoided for that patient.

What does a high NAFLD fibrosis score mean?+

A score above 0.676 predicts the presence of advanced (F3-F4) fibrosis with a positive predictive value around 90%, and generally warrants further evaluation such as transient elastography or a liver biopsy to confirm the fibrosis stage.

What happens when the score falls in the indeterminate zone?+

Scores between -1.455 and 0.676 cannot reliably classify fibrosis stage either way. Roughly a quarter to a third of patients fall in this zone and typically need a follow-up test — such as transient elastography (FibroScan) or a liver biopsy — to resolve the uncertainty.

What units does the calculator expect?+

Age in years, BMI in kg/m², platelet count in ×10⁹ per liter, and albumin in g/dL. AST and ALT can be entered in any consistent unit (typically U/L) since only their ratio is used.

What is the NAFLD fibrosis score used for?+

It is a non-invasive screening tool used to risk-stratify patients with nonalcoholic fatty liver disease (NAFLD) or NASH for advanced fibrosis, helping clinicians decide who needs specialist referral, elastography, or biopsy versus routine follow-up.

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