How the LDL Cholesterol Calculator works
Low-density lipoprotein (LDL) cholesterol is a major target in cardiovascular risk management. Many laboratories do not measure LDL directly; instead they calculate it from total cholesterol, HDL cholesterol and triglycerides.
The Friedewald equation (1972) is the classic method. It estimates very-low-density lipoprotein (VLDL) cholesterol as triglycerides ÷ 5 (in mg/dL) and subtracts it, along with HDL, from total cholesterol.
Required inputs
- Total cholesterol
- HDL cholesterol
- Triglycerides
Cholesterol mmol/L × 38.67 = mg/dL; triglycerides mmol/L × 88.57 = mg/dL.
Formula used
In mmol/L the triglyceride term is triglycerides ÷ 2.2. This calculator converts to mg/dL first and shows the result in both units.
Worked example
Total cholesterol 200 mg/dL, HDL 50 mg/dL, triglycerides 150 mg/dL:
- LDL = 200 − 50 − (150 ÷ 5) = 200 − 50 − 30 = 120 mg/dL (≈ 3.10 mmol/L)
Interpreting the result
LDL categories from the NCEP Adult Treatment Panel III (shown for education):
| LDL-C (mg/dL) | NCEP ATP III category |
|---|---|
| < 100 | Optimal |
| 100–129 | Near or above optimal |
| 130–159 | Borderline high |
| 160–189 | High |
| ≥ 190 | Very high |
Current ACC/AHA guidelines individualize LDL goals by overall cardiovascular risk rather than using a single target. Clinical decisions should follow current lipid guidelines and a clinician's advice.
Limitations
- Not valid when triglycerides are 400 mg/dL (4.5 mmol/L) or higher — the calculator will not show a result in that case.
- Tends to underestimate LDL when triglycerides are elevated and LDL is low (e.g. below 70 mg/dL); newer equations (Martin/Hopkins, NIH/Sampson) or direct LDL measurement may be more accurate.
- Less reliable in non-fasting samples with high triglycerides and in certain lipid disorders (e.g. type III dysbetalipoproteinemia).
- A calculated LDL is different from a directly measured LDL — always note which one a lab report shows.