What is the Friedewald equation?

Published by Friedewald, Levy, and Fredrickson in 1972, the equation estimates LDL as: LDL = Total Cholesterol - HDL - (Triglycerides / 5) in mg/dL, or LDL = Total Cholesterol - HDL - (Triglycerides / 2.2) in mmol/L. The Triglycerides / 5 term estimates VLDL cholesterol.

When does this formula become inaccurate?

The Friedewald equation is unreliable when fasting triglycerides exceed 400 mg/dL (4.5 mmol/L), when the patient is non-fasting, or in type III hyperlipoproteinemia. In those cases, a direct LDL measurement or the Martin-Hopkins equation should be used.

Why is the divisor 5 in mg/dL but 2.2 in mmol/L?

The divisor converts triglycerides to VLDL cholesterol. VLDL particles carry roughly 1/5 of their weight as cholesterol in mg/dL units. In mmol/L, the conversion factor is 2.2 due to the different molar mass scaling.

What is a healthy LDL level?

General guidelines from NCEP ATP III consider LDL below 100 mg/dL (2.59 mmol/L) optimal. Levels 100–129 are near optimal, 130–159 borderline high, 160–189 high, and 190+ very high. Individual targets depend on cardiovascular risk — consult your doctor.

Is this tool a substitute for medical advice?

No. This is an educational calculator. Always have a qualified healthcare provider interpret your lipid panel and guide any treatment decisions.

LDL Cholesterol Calculator (Friedewald)

Enter total cholesterol, HDL, and triglycerides to estimate LDL with a full Friedewald equation step-by-step breakdown.

Lipid Panel Values

Use fasting values from a standard blood test.

Input Unit

Total Cholesterol (mg/dL)

HDL Cholesterol (mg/dL)

Triglycerides (mg/dL)

Enter your lipid panel values and click Calculate LDL.

Estimated LDL

— mg/dL

—

Friedewald Equation — Step by Step

Estimate VLDL from Triglycerides

Apply Friedewald equation

Result

Values in Both Units

Measurement	mg/dL	mmol/L

LDL Reference Ranges

Optimal <100 mg/dL / <2.59 mmol/L

Near Optimal 100–129 / 2.59–3.34

Borderline High 130–159 / 3.37–4.12

High 160–189 / 4.14–4.90

Very High ≥190 / ≥4.92

NCEP ATP III / AHA guidelines. Consult your physician for personalized targets.

Summary

This tool applies the Friedewald equation to estimate LDL cholesterol from a standard lipid panel — total cholesterol, HDL, and triglycerides. Unlike a simple result display, it walks through each step of the formula so you can see exactly how VLDL is derived and how LDL is calculated. Results are shown in both mg/dL and mmol/L simultaneously, and the tool warns you when triglycerides exceed the 400 mg/dL threshold where the equation becomes unreliable.

How it works

Enter your total cholesterol, HDL, and triglycerides from a fasting lipid panel.
Choose mg/dL or mmol/L — both unit results are displayed at once.
The tool calculates VLDL as Triglycerides / 5 (mg/dL) or Triglycerides / 2.2 (mmol/L).
LDL is then derived as Total Cholesterol minus HDL minus VLDL.
Each arithmetic step is shown with your actual numbers substituted into the formula.
A color-coded category label maps your LDL to standard cardiovascular risk ranges.

Use cases

Verify LDL estimation when only a paper lipid panel is available.
Teach patients or students how the Friedewald equation works step by step.
Cross-check a reported LDL value against raw lipid numbers.
View mg/dL and mmol/L equivalents side by side without manual conversion.
Confirm whether triglycerides are within the reliable range for the formula.
Track estimated LDL changes over time with diet or medication adjustments.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu