FIB-4 Calculator: Check Your Liver Scarring Risk Score

TL;DR

• FIB-4 turns four routine numbers (age, AST, ALT and platelet count) into one score that estimates your risk of advanced liver scarring. The calculator above does the math.
• Below 1.3 is low risk (the calculator above uses 2.0 from age 65), 1.3–2.67 is indeterminate and above 2.67 is high risk. The score is unreliable under age 35.
• It’s a first step, not a diagnosis. An indeterminate or high score usually leads to a FibroScan or an ELF blood test.

FIB-4 is a free score that estimates your chance of advanced liver scarring (fibrosis) from four numbers you probably already have: your age, AST, ALT and platelet count. A result below 1.3 makes advanced fibrosis unlikely, while a result above 2.67 means it’s worth talking to your doctor about further tests.

The calculator above does the arithmetic, and nothing you type leaves the page. This guide explains where to find each number on your lab report, how to read your score, what “indeterminate” means, and why FIB-4 is less accurate for some people.

How Do I Use the FIB-4 Calculator?

You need four values, ideally from the same recent blood draw:

Input	Where to find it on your report	Tips
Age	Your age in years on the day of the test	Under 35, the score is unreliable
AST	Liver panel or comprehensive metabolic panel; sometimes labeled SGOT	U/L and IU/L are the same unit
ALT	Same panel; sometimes labeled SGPT	Use the number, not the flag
Platelets	Complete blood count (CBC); often labeled PLT	Enter it in 10⁹/L, which is the same number as 10³/µL or K/µL

The platelet unit is where most mistakes happen. US reports usually show something like “250 K/µL” or “250 × 10³/µL,” which you enter as 250. If your report shows the full count, such as 250,000 per microliter, divide by 1,000 and enter 250. MedlinePlus gives an example normal platelet range of 150 to 400 × 10⁹/L.

If any of your values are flagged high or low, enter them anyway. The calculator above doesn’t need normal results; it needs accurate ones.

What Is the FIB-4 Formula?

FIB-4 = (Age × AST) ÷ (Platelets × √ALT)

Age is in years, AST and ALT are in U/L, and platelets are in 10⁹/L. The score was developed in 2006 by Sterling and colleagues in people with HIV and hepatitis C. It has since been widely studied in fatty liver, and both the AASLD and the European guideline now recommend it as the first step for people with MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD).

Here’s a worked example. A 55-year-old with AST 32, ALT 40 and platelets 210:

(55 × 32) ÷ (210 × √40) = 1,760 ÷ (210 × 6.32) = 1,760 ÷ 1,328 = 1.33

The score goes up when AST rises relative to ALT (see our guide to the AST/ALT ratio) and when platelets fall, both of which can happen as scarring advances. Age is in the top half of the formula, so older people score higher with the same labs.

What Does My FIB-4 Score Mean?

These bands come from the AASLD 2023 guidance and the 2024 European guideline.

Your FIB-4	Risk of advanced fibrosis	What usually happens next
Below 1.3 (below 2.0 from age 65 in the calculator above)	Low	Managed by your regular doctor, with lifestyle changes and a periodic recheck
1.3–2.67 (2.0–2.67 from 65)	Indeterminate	A second test, usually a FibroScan or an ELF blood test
Above 2.67	High	A second test, and referral to a gastroenterologist or hepatologist should be considered
Any score under age 35	Unreliable	A second test may be considered if you have metabolic risk factors or raised liver enzymes

You may see older cutoffs of 1.45 and 3.25 on some calculators. Those come from the original 2006 study. Different guidelines and calculators draw the lines slightly differently, so your doctor’s reading wins over any table. No single score is a diagnosis: your doctor will look at the trend and your other results.

Here’s how the bands play out with example numbers:

Example	Age	AST	ALT	Platelets	FIB-4	Band
A	48	28	45	260	0.77	Low
B	55	32	40	210	1.33	Indeterminate, just over the line
C	66	30	28	200	1.87	Low, because the cutoff is 2.0 at this age
D	50	45	30	120	3.42	High

Example B shows how close to the line some results sit. A slightly different AST or platelet count on another day could move it into the low band, which is one reason doctors look at the trend.

Why Is the Cutoff Different Over 65?

Because age multiplies the top of the formula, FIB-4 rises with age even when the liver hasn’t changed. With the same AST 30, ALT 30 and platelets 200, a 50-year-old scores 1.37 and a 60-year-old scores 1.64.

Using 1.3 in older adults would label many people “indeterminate” who don’t have advanced scarring. So both the AASLD and the European guideline use a low-risk cutoff of 2.0 for people over 65. The calculator above switches to 2.0 from age 65. The high-risk cutoff of 2.67 stays the same at every age.

What Does an Indeterminate FIB-4 Mean?

An indeterminate score (1.3–2.67) means FIB-4 can’t rule advanced scarring in or out. It doesn’t mean you have it. The European guideline points out that FIB-4’s predictive value is low above 1.3, so many people in this range turn out not to have advanced fibrosis.

The AASLD recommends a second test for anyone with FIB-4 of 1.3 or higher:

Second test	What it is	Low risk	High risk
FibroScan (VCTE)	A quick, painless scan that measures liver stiffness	Under 8 kPa	12 kPa or more
ELF test	A blood test of three markers of scar tissue turnover	Below 7.7	9.8 or more

If the second test is also intermediate or high, the AASLD advises referral to specialty care for further evaluation. Our guide to FibroScan results explains what the stiffness and fat numbers mean.

Why Does FIB-4 Have Low Accuracy in Some People?

People often search for “FIB-4 has low accuracy.” The phrase comes straight from the AASLD guidance, which states that “FIB-4 has low accuracy in those under age 35” and recommends considering a second test in younger people who have metabolic risk factors or raised liver enzymes. The European guideline also says FIB-4 performs poorly under 35.

That’s not the only limit. The European guideline lists several more:

• The middle range. Its ability to detect fibrosis is limited between 1.3 and 2.67.
• Older adults. Accuracy drops with age, which is why the cutoff changes over 65.
• Type 2 diabetes. FIB-4 is less reliable in people with diabetes. The AASLD recommends rechecking every 1–2 years in this group for that reason.
• False positives. Used alone, especially in people with a low chance of disease, it flags many who turn out to be fine.
• Missed cases. The guideline notes that FIB-4 will miss around 10% of people with advanced fibrosis.

The AASLD adds that FIB-4 shouldn’t be used in people who are acutely ill. And because the score is built from AST, ALT and platelets, anything that moves those numbers for non-liver reasons moves the score too. A hard workout or muscle injury can raise AST, and some medicines and conditions lower platelets.

So why use it? The AASLD acknowledges that FIB-4 is statistically inferior to the ELF test and to elastography, but still recommends it as the first step because it’s simple and adds little or no cost. Its strength is ruling out advanced scarring in most people, so that second tests go to the people who need them.

How Often Should You Recheck FIB-4?

If your score is low, the AASLD suggests:

• Every 2–3 years if you don’t have prediabetes or type 2 diabetes and have one or two metabolic risk factors.
• Every 1–2 years if you have prediabetes, type 2 diabetes, or two or more metabolic risk factors.

The European guideline suggests every 1–3 years for a low score. Over time, the AASLD notes that moving from low to intermediate to high risk may signal that the disease is progressing.

When you compare scores, remember that the age part of the formula pushes the number up a little every year. A small rise with stable AST, ALT and platelets is expected. A jump driven by a falling platelet count or a rising AST is the kind of change to raise with your doctor.

Can You Lower Your FIB-4 Score?

The score itself isn’t the goal; a healthier liver is. But FIB-4 can improve when the liver does. The AASLD notes that improvements in FIB-4 have been associated with improvement seen on liver biopsy, although the exact thresholds still need validating.

The levers are the same ones that protect the liver:

• Weight loss, if you carry extra. The 2024 European guideline aims for a sustained loss of at least 5% to reduce liver fat, 7–10% to improve inflammation and 10% or more to improve fibrosis. Our guide on how to reverse fatty liver covers the full plan.
• Less alcohol. The AASLD advises people with significant scarring (stage F2 or higher) to avoid alcohol completely.
• Good blood sugar control if you have prediabetes or diabetes.

The same calculator is built into the Liverly app’s settings if you’d rather keep it on your phone.

Before You Calculate

A few habits make the score more meaningful:

1. Use recent results from one blood draw, so the four numbers describe the same moment.
2. Avoid a hard workout right before the blood test, since it can push AST up. Our AST blood test guide explains why muscle matters.
3. Don’t calculate during an acute illness, when the AASLD says FIB-4 shouldn’t be used.
4. Check the platelet units before you enter them.
5. Bring the result to your doctor, along with the full report. Our guide to liver function test results explains the other numbers on it, and ALT and AST levels in fatty liver covers why normal enzymes don’t rule out scarring.

The calculator above is an educational estimate, not a diagnosis. It can’t replace your doctor’s assessment, which takes in your history, an exam and other tests.

The Bottom Line

FIB-4 is the simplest way to estimate your risk of advanced liver scarring, using your age, AST, ALT and platelet count. Below 1.3 is low risk (2.0 from age 65), 1.3–2.67 is indeterminate, and above 2.67 is high. It’s least reliable under 35, in older adults, in people with diabetes and in the middle range, which is why an indeterminate or high score leads to a FibroScan or ELF test rather than a diagnosis. Work out your score, recheck it on the schedule your doctor sets, and watch the trend.

Sources

• AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease (Rinella et al., Hepatology 2023)
• EASL–EASD–EASO Clinical Practice Guidelines on the management of MASLD (Obesity Facts 2024)
• Sterling et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection (Hepatology 2006)
• MedlinePlus: Platelet count

This article is for informational purposes only and is not medical advice. Talk to your doctor or hepatologist about your specific situation.