Friedewald formula: how calculated LDL cholesterol works

The Friedewald formula estimates LDL cholesterol from total cholesterol, HDL cholesterol, and triglycerides. It made routine LDL reporting practical, but calculated LDL is an approximation whose reliability changes with the sample.

Use our LDL calculator to run the equation and view the limitations with your result.

Why LDL is often calculated

Measuring every lipoprotein fraction with reference laboratory methods is slow and expensive. A standard lipid panel already measures total cholesterol, HDL, and triglycerides, allowing LDL to be estimated without a separate complex procedure.

The formula assumes that very-low-density lipoprotein cholesterol can be approximated from triglycerides. That assumption works reasonably in many routine samples and less well in others.

How the Friedewald formula works

When values use mg/dL:

LDL-C = total cholesterol − HDL-C − (triglycerides ÷ 5)

When values use mmol/L:

LDL-C = total cholesterol − HDL-C − (triglycerides ÷ 2.2)

Do not use the divisor from one unit system with values from the other.

Worked calculated LDL example

For total cholesterol 200 mg/dL, HDL 50 mg/dL, and triglycerides 150 mg/dL:

• 150 ÷ 5 = 30 mg/dL estimated VLDL cholesterol
• 200 − 50 − 30 = 120 mg/dL calculated LDL

This is not a direct count of LDL particles and does not reveal LDL size or apoB.

When the Friedewald estimate is unreliable

The traditional equation is not used when triglycerides are 400 mg/dL or higher. Accuracy can also decline at lower LDL values and as triglycerides rise. Nonfasting samples, diabetes, kidney disease, and unusual lipoprotein patterns can add uncertainty.

Modern laboratories may use the Martin-Hopkins or Sampson equation, or measure LDL directly, depending on their system and the sample. Read the method printed on your report before comparing two LDL results.

What to use when calculated LDL is uncertain

Non-HDL cholesterol needs only total and HDL cholesterol, so it remains easy to calculate when triglycerides complicate LDL estimation. See our non-HDL calculation guide.

ApoB can help estimate the number of atherogenic particles, while lipoprotein(a) identifies an inherited risk factor not visible in ordinary LDL. Current guidance uses these selectively rather than requiring them for everyone.

How calculated LDL fits with ratios

The cholesterol ratio chart and TG/HDL guide offer additional views, but treatment decisions should not be reverse-engineered from a ratio when the underlying LDL or non-HDL value is concerning.

The bottom line

The Friedewald formula is useful because it is simple and often adequate. Treat “calculated” as a method label, not a flaw, while recognizing the samples where a different equation or measurement is more appropriate.