LDL Cholesterol Calculator

Calculator

How we calculate it

Most laboratories do not measure LDL cholesterol directly; they calculate it from total cholesterol, HDL and triglycerides. This tool offers two equations and tells you which it used. The default is NIH Equation 2, published by Sampson and colleagues in JAMA Cardiology in 2020 and validated against beta-quantification — the laboratory reference method. It remains usable up to 800 mg/dL of triglycerides and is more accurate than the alternative when LDL is low or triglycerides are raised. The second option is the Friedewald equation from 1972, still reported by many laboratories: total cholesterol minus HDL minus triglycerides divided by five. Friedewald requires a fasting sample and is not valid at 400 mg/dL of triglycerides or above, and the tool refuses to return a number past that limit rather than producing one that looks plausible. A third contemporary method, the Martin-Hopkins equation, uses an adjustable factor drawn from a published 180-cell lookup table; it is deliberately not implemented here, because an approximation of that table would be wrong in ways a reader could not detect. It is named in the limitations so you know why a laboratory result may differ.

Important limitations

• This is a calculated, not a measured, LDL. It inherits the measurement error in all three values it is derived from.
• Equations disagree with each other, particularly when LDL is below 70 mg/dL or triglycerides are above about 150 mg/dL. Your laboratory may use Friedewald, Martin-Hopkins or a direct assay, and may report a different number from the same sample.
• The Martin-Hopkins equation, another widely adopted contemporary method, is not implemented here because it depends on a lookup table that cannot responsibly be approximated.
• A directly measured LDL is preferable when triglycerides are high, when LDL is very low, in known genetic lipid disorders, and where a treatment decision turns on a precise value.
• The Friedewald equation requires a 9–12 hour fasting sample. A non-fasting sample raises triglycerides and makes it less reliable.
• Guideline LDL targets are risk-based and considerably lower than the general ranges shown here for people at high risk. The ranges are orientation only.
• An LDL value is not a diagnosis and does not by itself determine whether treatment is needed.