Why does the Friedewald formula need triglycerides?

TG/5 (in mg/dL) approximates the cholesterol carried by VLDL particles. That estimate is what lets us back out LDL from TC and HDL without spinning the sample down.

When is Friedewald inaccurate?

When triglycerides exceed 400 mg/dL (4.52 mmol/L), or when LDL is very low (under 70 mg/dL), Friedewald underestimates LDL. Newer formulas (Martin–Hopkins, Sampson–NIH) handle those edge cases better, but a direct LDL measurement is the gold standard.

What does “LDL” actually measure?

LDL is the cholesterol carried inside low-density lipoprotein particles. Higher LDL is associated with a higher long-term risk of atherosclerotic cardiovascular disease.

Are the NCEP ATP III bands still current?

The ATP III thresholds (2002) are the most commonly cited LDL category labels. Newer guidelines (ACC/AHA, ESC) emphasise absolute cardiovascular risk plus LDL, not LDL alone — so use the band for context, not as a target.

Is my lab data stored?

No. Everything runs in your browser.

LDL Cholesterol Calculator

Written by Golam Rabbani, Founder & Lead Engineer — Last updated 2026-05-01

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this ldl cholesterol calculator

Pick mg/dL or mmol/L — switching the unit converts every value already on the form.
Enter total cholesterol (TC), HDL cholesterol, and triglycerides from your lipid panel.
Press “Calculate LDL” to apply the Friedewald formula and see the NCEP ATP III risk band.
If triglycerides exceed the Friedewald validity ceiling (400 mg/dL or 4.52 mmol/L) the tool refuses to estimate — ask your lab for a direct LDL measurement instead.
Use Copy to save the result or Reset to clear the form.

About this ldl cholesterol calculator

The LDL cholesterol calculator estimates low-density lipoprotein cholesterol from a standard lipid panel using the Friedewald formula: LDL = TC − HDL − TG ÷ 5 (in mg/dL), or LDL = TC − HDL − TG ÷ 2.2 in mmol/L. It then maps the result to the NCEP ATP III risk bands — optimal (<100 mg/dL), near optimal (100–129), borderline high (130–159), high (160–189), and very high (≥ 190).

Friedewald assumes a constant TC:VLDL ratio, which breaks down when triglycerides are very high; the original paper (Friedewald, Levy & Fredrickson, J Clin Pathol 1972) limits the formula to TG ≤ 400 mg/dL. Above that, this tool refuses to fabricate a number and tells you to ask the lab for a direct LDL — exactly what a careful clinician would do.

Worked example: TC 200 mg/dL, HDL 50 mg/dL, TG 150 mg/dL. LDL = 200 − 50 − 150/5 = 200 − 50 − 30 = 120 mg/dL, which falls in the near-optimal band per NCEP ATP III.

This calculator is for general information using a published formula and is not a substitute for a clinician-interpreted lipid panel. This calculator is for general educational purposes only and is not medical advice — consult a licensed healthcare professional for personal guidance.

FAQ

Why does the Friedewald formula need triglycerides?: TG/5 (in mg/dL) approximates the cholesterol carried by VLDL particles. That estimate is what lets us back out LDL from TC and HDL without spinning the sample down.
When is Friedewald inaccurate?: When triglycerides exceed 400 mg/dL (4.52 mmol/L), or when LDL is very low (under 70 mg/dL), Friedewald underestimates LDL. Newer formulas (Martin–Hopkins, Sampson–NIH) handle those edge cases better, but a direct LDL measurement is the gold standard.
What does “LDL” actually measure?: LDL is the cholesterol carried inside low-density lipoprotein particles. Higher LDL is associated with a higher long-term risk of atherosclerotic cardiovascular disease.
Are the NCEP ATP III bands still current?: The ATP III thresholds (2002) are the most commonly cited LDL category labels. Newer guidelines (ACC/AHA, ESC) emphasise absolute cardiovascular risk plus LDL, not LDL alone — so use the band for context, not as a target.
Is my lab data stored?: No. Everything runs in your browser.