Free tool

LDL Cholesterol Calculator (Friedewald & NIH Equations)

Q: Why is LDL calculated instead of measured?

Most routine lipid panels estimate LDL from the other three values because the direct assay costs more and the estimate is accurate for most people. The Friedewald equation subtracts HDL and a fifth of the triglycerides from total cholesterol; it loses accuracy as triglycerides rise, which is why laboratories switch to a direct LDL or a newer equation at 400 mg/dL.

Q: What is the difference between Friedewald and the Sampson/NIH equation?

Friedewald (1972) assumes triglyceride-rich particles carry a fixed fifth of their weight as cholesterol, which fails at high triglycerides and at low LDL. The Sampson/NIH equation (2020) was fitted to ultracentrifugation data and stays accurate up to triglycerides of about 800 mg/dL and at LDL values below 70, where modern treatment targets sit.

Q: What is non-HDL cholesterol and why does it matter?

Non-HDL is total cholesterol minus HDL — the cholesterol in every plaque-forming particle, including the triglyceride-rich ones the LDL number misses. It needs no fasting and is a secondary target in the 2018 AHA/ACC guideline, usually set about 30 mg/dL above the LDL goal.

Q: Do I need to fast for the inputs?

For an accurate estimate, yes: triglycerides rise for hours after a meal and inflate the correction term, lowering the calculated LDL. Guidelines accept non-fasting panels for screening, but a value near a treatment threshold should come from a 9–12 hour fast or a direct LDL measurement.

The short answer

Enter total cholesterol, HDL and fasting triglycerides and the calculator estimates LDL cholesterol with the Friedewald equation when triglycerides are under 400 mg/dL and the newer Sampson/NIH equation when they are higher, and shows non-HDL cholesterol and the total-to-HDL ratio alongside. The LDL is read against the NCEP categories — optimal under 100, borderline high 130–159, high 160 and above.

Inputs: Total · HDL · triglycerides
Equations: Friedewald · Sampson/NIH
Also shown: Non-HDL · TC:HDL
Cost: Free

Total cholesterol

mg/dL

Total Cholesterol range

HDL cholesterol

mg/dL

HDL Cholesterol range

Triglycerides (fasting)

mg/dL

Fasting 9–12 h; the estimate degrades as triglycerides rise · Triglycerides range

Enter your values to calculate.

Friedewald: LDL = total − HDL − triglycerides ÷ 5 · Sampson/NIH: LDL = TC/0.948 − HDL/0.971 − (TG/8.56 + TG×non-HDL/2140 − TG²/16100) − 9.44 · non-HDL = total − HDL (all mg/dL)

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

How the LDL cholesterol is calculated

Friedewald: LDL = total − HDL − triglycerides ÷ 5 · Sampson/NIH: LDL = TC/0.948 − HDL/0.971 − (TG/8.56 + TG×non-HDL/2140 − TG²/16100) − 9.44 · non-HDL = total − HDL (all mg/dL)

Worked example

Total cholesterol (mg/dL)	HDL cholesterol (mg/dL)	Triglycerides (fasting) (mg/dL)	LDL cholesterol (mg/dL)
210	50	150	130

Equation used: Friedewald (triglycerides < 400) · Sampson/NIH estimate: 133 mg/dL · Non-HDL cholesterol: 160 mg/dL · Total : HDL ratio: 4.2

Falls in: Borderline high.

How to read the result

LDL cholesterol	Reads as	What it usually means
< 100	Optimal	Under 100 mg/dL is the optimal range in the NCEP categories US laboratories print. People with established heart or vascular disease are usually treated to below 70 (below 55 after repeated events), so 'optimal' still depends on your overall risk.
100 – 130	Near optimal	100–129 mg/dL is near or above optimal. For most adults without other risk factors this is managed with lifestyle; the ten-year cardiovascular risk estimate, not the LDL alone, decides whether medication is discussed.
130 – 160	Borderline high	130–159 mg/dL. Whether this needs treatment depends on age, blood pressure, HDL, diabetes, smoking and family history — the inputs to the ten-year risk calculator. A TSH is worth checking if the value is new, since an underactive thyroid raises LDL.
160 – 190	High	160–189 mg/dL is high by every guideline. Statin therapy is commonly recommended when overall risk is elevated, and secondary causes (hypothyroidism, nephrotic syndrome, cholestatic liver disease, some medications, very low-carbohydrate diets) are excluded first.
≥ 190	Very high	190 mg/dL or more at any age raises the question of familial hypercholesterolemia, an inherited condition affecting about 1 in 250 people; guidelines recommend treatment regardless of the risk score and a check of first-degree relatives. Confirm with a repeat fasting panel or a direct LDL.

Cut points reviewed by Youmna DiStefano, MD on 2026-10-12. Sources below.

Limits

Both equations estimate LDL from a fasting panel; they are not measurements. Friedewald becomes unreliable as triglycerides rise and is invalid at 400 mg/dL and above; the Sampson/NIH equation stays accurate to about 800 and at low LDL values. A non-fasting sample inflates triglycerides and lowers the estimate. When the estimate sits near a treatment threshold, or triglycerides are high, a direct LDL or apolipoprotein B measurement is the better basis for a decision. The bands are the NCEP ATP III categories; individual goals follow the 2018 AHA/ACC guideline and your clinician's risk assessment.

Sources

Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem 1972;18:499–502. doi.org/10.1093/clinchem/18.6.499
Sampson M, et al. A New Equation for Calculation of Low-Density Lipoprotein Cholesterol in Patients With Normolipidemia and/or Hypertriglyceridemia. JAMA Cardiol 2020;5:540–548. doi.org/10.1001/jamacardio.2020.0013
Grundy SM, et al. 2018 AHA/ACC/Multisociety Guideline on the Management of Blood Cholesterol. Circulation 2019;139:e1082–e1143. doi.org/10.1161/CIR.0000000000000625
Martin SS, et al. Comparison of a Novel Method vs the Friedewald Equation for Estimating Low-Density Lipoprotein Cholesterol Levels From the Standard Lipid Profile. JAMA 2013;310:2061–2068. doi.org/10.1001/jama.2013.280532

Frequently asked questions

Why is LDL calculated instead of measured?

Most routine lipid panels estimate LDL from the other three values because the direct assay costs more and the estimate is accurate for most people. The Friedewald equation subtracts HDL and a fifth of the triglycerides from total cholesterol; it loses accuracy as triglycerides rise, which is why laboratories switch to a direct LDL or a newer equation at 400 mg/dL.

What is the difference between Friedewald and the Sampson/NIH equation?

Friedewald (1972) assumes triglyceride-rich particles carry a fixed fifth of their weight as cholesterol, which fails at high triglycerides and at low LDL. The Sampson/NIH equation (2020) was fitted to ultracentrifugation data and stays accurate up to triglycerides of about 800 mg/dL and at LDL values below 70, where modern treatment targets sit.

What is non-HDL cholesterol and why does it matter?

Non-HDL is total cholesterol minus HDL — the cholesterol in every plaque-forming particle, including the triglyceride-rich ones the LDL number misses. It needs no fasting and is a secondary target in the 2018 AHA/ACC guideline, usually set about 30 mg/dL above the LDL goal.

Do I need to fast for the inputs?

For an accurate estimate, yes: triglycerides rise for hours after a meal and inflate the correction term, lowering the calculated LDL. Guidelines accept non-fasting panels for screening, but a value near a treatment threshold should come from a 9–12 hour fast or a direct LDL measurement.

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.