LDL Cholesterol Calculator (Friedewald & NIH Equation)
Calculate LDL cholesterol from total cholesterol, HDL and triglycerides with the Friedewald and NIH (Sampson) equations, in mg/dL or mmol/L.
Most lab reports do not measure LDL ("bad") cholesterol directly — they calculate it from total cholesterol, HDL and triglycerides. This calculator shows the classic Friedewald estimate and the NIH (Sampson) equation published in 2020, which was evaluated at triglyceride levels up to 800 mg/dL. Enter the three numbers from your lipid panel to check your report or see which band your LDL falls in.
How to use this tool
- Choose mg/dL or mmol/L to match your lab report.
- Enter total cholesterol, HDL cholesterol and triglycerides.
- Compare the two LDL estimates; the category is based on the NIH equation.
Formula
Friedewald: LDL = TC − HDL − TG ÷ 5, with all concentrations in mg/dL.
NIH: LDL = TC ÷ 0.948 − HDL ÷ 0.971 − (TG ÷ 8.56 + TG × non-HDL ÷ 2140 − TG² ÷ 16100) − 9.44
TC is total cholesterol, TG triglycerides and non-HDL = TC − HDL. Both equations work in mg/dL, so mmol/L values are converted with 38.67 for cholesterol and 88.57 for triglycerides and the answer is converted back. Friedewald is not used when triglycerides are 400 mg/dL (4.5 mmol/L) or more; the NIH equation was validated up to 800 mg/dL.
Example
With total cholesterol 200, HDL 50 and triglycerides 150 mg/dL, Friedewald gives 200 − 50 − 30 = 120 mg/dL. The NIH equation gives 210.97 − 51.49 − 26.64 − 9.44 ≈ 123 mg/dL, and non-HDL cholesterol is 150 mg/dL. Both LDL figures sit in the 100–129 "near or above optimal" band.
Frequently asked questions
Why does my lab report show a different LDL?
Laboratories may use Friedewald, Sampson, Martin–Hopkins or an assay. Those methods and unit rounding can yield different values. An unexplained discrepancy should be checked with the laboratory rather than assuming this estimate is the correct one.
What is a good LDL level?
The historical ATP III descriptive band below 100 mg/dL is called optimal. Your treatment target may be different and depends on overall cardiovascular risk and medical history. A calculated category is not an individual treatment recommendation.
Do I need to fast before a cholesterol test?
Not always. Non-fasting tests are widely accepted for routine checks, but triglycerides rise after a meal and make calculated LDL less accurate, so a fasting sample or a direct LDL may be requested when triglycerides are high.
Sources
- Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of LDL cholesterol in plasma. Clin Chem, 1972
- Sampson M et al. A new equation for calculation of LDL cholesterol in patients with normolipidemia and/or hypertriglyceridemia. JAMA Cardiol, 2020
- NHLBI — ATP III At-A-Glance: Quick Desk Reference
This tool gives an estimate for general information only. It is not financial, tax, legal or medical advice — check with a qualified professional before you rely on the result.
Last updated: 2026-10-30