Most labs calculate LDL rather than measuring it. Friedewald (1972) assumes VLDL cholesterol is one fifth of triglycerides, which becomes inaccurate when triglycerides are high or LDL is very low. The Sampson equation (2020) was developed at the NIH to fix this and is valid up to 800 mg/dL triglycerides.
How to use the LDL Calculator
- Total cholesterol
- HDL cholesterol
- Triglycerides
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the three values from a lipid panel, ideally fasting. The calculator applies both equations; Friedewald is not shown as valid when triglycerides exceed 400 mg/dL.
LDL categories (NCEP ATP III)
| LDL | mmol/L | Category |
|---|---|---|
| below 100 mg/dL | below 2.6 | Optimal |
| 100–129 | 2.6–3.3 | Near optimal |
| 130–159 | 3.4–4.1 | Borderline high |
| 160–189 | 4.1–4.9 | High |
| 190 and above | 4.9 and above | Very high |
Tips
- Use results from the same fasting state the formula expects (most lipid formulas assume fasting).
- Check the units on your lab report before entering values.
- Discuss treatment targets with your clinician, since they depend on your overall risk.
- Repeat abnormal results; a single value can be misleading.
Common mistakes to avoid
- Using Friedewald LDL when triglycerides are above 400 mg/dL.
- Mixing mg/dL and mmol/L values in one calculation.
- Ignoring other risk factors such as smoking and blood pressure.
Inputs explained
| Field | What to enter |
|---|---|
| Total cholesterol | Units: mg/dL, mmol/L |
| HDL cholesterol | Units: mg/dL, mmol/L |
| Triglycerides | Units: mg/dL, mmol/L |
What each result means
- LDL: Friedewald = [Total cholesterol] – [HDL cholesterol] – [Triglycerides]÷5
- LDL: Sampson (NIH) = [Total cholesterol]÷0.948 – [HDL cholesterol]÷0.971 – ([Triglycerides]÷8.56 + [Triglycerides]×([Total cholesterol] – [HDL cholesterol])÷2140 – [Triglycerides]^2÷16100) – 9.44
- Non-HDL cholesterol = [Total cholesterol] – [HDL cholesterol]
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Friedewald: LDL = TC − HDL − TG ÷ 5 (mg/dL)
Sampson/NIH: LDL = TC/0.948 − HDL/0.971 − (TG/8.56 + TG × non-HDL/2140 − TG²/16100) − 9.44
Non-HDL = TC − HDL
Worked example
Inputs: Total cholesterol: 200 mg/dL; HDL cholesterol: 50 mg/dL; Triglycerides: 150 mg/dL.
Results: LDL – Friedewald = 120 mg/dL; LDL – Sampson (NIH) = 123 mg/dL; Non-HDL cholesterol = 150 mg/dL; Friedewald valid? = Yes; LDL category (ATP III) = Near optimal.
Key terms
- LDL
- Low-density lipoprotein cholesterol.
- VLDL
- Very-low-density lipoprotein.
- Non-HDL
- All the cholesterol carried in atherogenic particles.
Frequently asked questions
What is a good LDL level?
Below 100 mg/dL (2.6 mmol/L) for most people; lower targets apply after a heart attack or with diabetes.
Do I need to fast?
Not usually, but fasting gives more reliable triglycerides.
Why are the two results different?
Friedewald underestimates LDL when triglycerides are high or LDL is low.