LDL Cholesterol Calculator.

On a standard lipid panel, total cholesterol, HDL, and triglycerides are measured directly — but LDL usually is not. Instead it is estimated by subtraction, because a direct LDL assay costs more and, until recently, added little. The classic method is the Friedewald equation, published in 1972: LDL = total cholesterol − HDL − (triglycerides ÷ 5). The "triglycerides ÷ 5" term estimates the cholesterol carried in VLDL particles.

That fixed divisor of 5 is Friedewald's weakness. It assumes a constant triglyceride-to-VLDL ratio, which breaks down when triglycerides are high or LDL is low — exactly the situations where an accurate number matters most. Friedewald is considered invalid above a triglyceride level of 400 mg/dL, where it systematically underestimates LDL.

Two newer methods fix this. The Sampson equation (NIH Equation 2, 2020) replaces the fixed divisor with a formula that accounts for both triglycerides and non-HDL cholesterol, and stays accurate up to a triglyceride level of 800 mg/dL. Because it is a closed-form equation, this calculator computes it exactly and shows it as the primary estimate.

The Martin-Hopkins method (2013) takes a different route: it replaces the divisor with a value drawn from a large lookup table of median triglyceride-to-VLDL ratios, stratified by a person's own triglyceride and non-HDL levels. It performs comparably to Sampson and is endorsed by several guideline groups, especially for very low LDL and non-fasting samples. Whichever method your lab uses, the takeaway is the same: when triglycerides are elevated, trust the modern equations over Friedewald.

LDL measures the cholesterol carried inside LDL particles — not the number of particles. Two people with the same LDL can carry very different particle counts, and it is particle number, measured as ApoB, that most directly drives atherosclerosis. When triglycerides are high, non-HDL cholesterol (total − HDL, also shown here) is a better target than LDL because it captures all the atherogenic particles, not just LDL.

Use this calculator to fill in a missing LDL or to check a lab's number, and pair it with ApoB or non-HDL when triglycerides are elevated. Any calculated LDL is an estimate — a direct assay is preferable when the number will change treatment.