LDL Cholesterol Calculator (Friedewald)

Calculate LDL cholesterol from a standard lipid panel using the Friedewald equation, with the Martin-Hopkins adjustable factor shown for comparison at low triglyceride and low LDL levels.

🧪 Lab Value📐 LDL = Total cholesterol − HDL − (Triglycerides / 5)🏥 Health
Total cholesterol (mg/dL)
HDL cholesterol (mg/dL)
Triglycerides (mg/dL)
Please enter valid values.

Formula & Reference

VariableSymbolFormulaUnits
LDL Cholesterol Calculator (Friedewald)—LDL = Total cholesterol − HDL − (Triglycerides / 5)mg/dL

Step-by-Step Examples

Example 1
Standard Panel

Total cholesterol 200, HDL 50, triglycerides 150 mg/dL.

  • VLDL estimate = 150 / 5 = 30
  • LDL = 200 − 50 − 30
  • LDL = 120 mg/dL
✓ LDL 120 mg/dL — near optimal
Example 2
Favourable Profile

Total cholesterol 165, HDL 62, triglycerides 80 mg/dL.

  • VLDL estimate = 80 / 5 = 16
  • LDL = 165 − 62 − 16
  • LDL = 87 mg/dL
✓ LDL 87 mg/dL — optimal range
Example 3
Elevated Triglycerides

Total cholesterol 260, HDL 38, triglycerides 420 mg/dL.

  • Triglycerides are at or above 400 mg/dL
  • The fixed 1:5 VLDL ratio breaks down at this level
  • Friedewald cannot be applied
✓ Direct LDL measurement required

Real-World Applications

🧪
Routine Lipid Reporting
Most laboratories report a calculated rather than measured LDL, because the calculation is far cheaper than direct assay.
💊
Treatment Targets
LDL is the primary lipid target in most cardiovascular prevention guidelines, making its accurate estimation clinically consequential.
📈
Progress Tracking
Serial calculated LDL values let patients and clinicians see whether diet, exercise, or medication changes are working.
📚
Clinical Chemistry Teaching
Friedewald is a classic example of a useful approximation with clearly defined boundary conditions.

Common Mistakes to Avoid

⚠️
Using Friedewald above 400 mg/dL triglycerides

The equation assumes a fixed triglyceride-to-VLDL ratio of 5:1. That assumption fails at high triglyceride levels, and the result becomes unreliable enough that laboratories suppress it.

⚠️
Ignoring underestimation at low LDL

Friedewald systematically underestimates LDL when values fall below roughly 70 mg/dL — exactly the range that matters most for high-risk patients on intensive therapy. The Martin-Hopkins equation was developed to address this.

⚠️
Comparing non-fasting and fasting samples interchangeably

Triglycerides rise after eating, so a non-fasting sample inflates the VLDL estimate and depresses calculated LDL. Serial comparisons should use consistent conditions.

Frequently Asked Questions

What is the Friedewald equation? ▾
LDL equals total cholesterol minus HDL minus triglycerides divided by five, where the last term estimates VLDL cholesterol from triglyceride concentration.
When can Friedewald not be used? ▾
When triglycerides reach 400 mg/dL or higher, where the fixed 5:1 ratio no longer holds, and with caution below 70 mg/dL LDL where it underestimates.
What is the Martin-Hopkins equation? ▾
A refinement that replaces the fixed divisor of five with a variable factor drawn from a lookup table based on non-HDL cholesterol and triglyceride levels, improving accuracy at low LDL.
Do I need to fast for an accurate LDL? ▾
Fasting mainly matters because it stabilises triglycerides. Many guidelines now accept non-fasting lipid panels for screening, reserving fasting samples for cases with high triglycerides.
Is non-HDL cholesterol a better target? ▾
Non-HDL captures all atherogenic particles and requires no calculation assumptions, which is why many guidelines now list it as a co-primary or secondary target alongside LDL.

Related Health Calculators

🧪 Non-HDL Cholesterol🧪 Cholesterol Ratios❤️ ASCVD 10-Year Risk❤️ Framingham Risk📊 Metabolic Syndrome