This calculator estimates LDL cholesterol from total cholesterol, HDL cholesterol, and triglycerides using the Friedewald equation. It returns a calculated value in mg/dL or mmol/L. It is not a direct LDL measurement, does not tell you whether the value is at a target, and does not replace the LDL value on your report.
What this calculator does
Many laboratories do not measure LDL cholesterol directly. They calculate it from total cholesterol, HDL cholesterol, and triglycerides, using an equation. The Friedewald equation is the oldest and most widely known of these calculations, and it is the one this page implements.
Because the result is derived, it carries the assumptions of the equation. The most important one is that the relationship between triglycerides and the cholesterol in triglyceride-rich particles is roughly fixed. When triglycerides are high, that assumption weakens, and the calculated value can be less reliable. A laboratory may then measure LDL directly or use a different equation.
The equation
The Friedewald equation, with all values in mg/dL:
LDL cholesterol = total cholesterol − HDL cholesterol − (triglycerides / 5)| Variable | Meaning |
|---|---|
| Total cholesterol | All cholesterol measured in the sample, in mg/dL. |
| HDL cholesterol | Cholesterol carried in HDL particles, in mg/dL. |
| Triglycerides | Triglyceride concentration, in mg/dL. |
| 5 | The fixed factor the equation uses for the triglyceride-rich fraction. |
| LDL cholesterol | The calculated cholesterol carried in LDL particles. |
How to use it
- Enter total cholesterol, HDL cholesterol, and triglycerides in the same unit. The calculator handles mg/dL and mmol/L.
- Use the values printed on the report, not values from different reports or different units.
- Check whether the report already prints an LDL value. If it does, that value is the one the laboratory reported, and it may use a different method.
- Read the result as a calculation. It does not replace the report's LDL, target, or comment.
What the result means, and what it does not
The result is an estimate of the cholesterol carried in LDL particles, calculated from the other three lines. It does not measure LDL particles directly, and it does not include apolipoprotein B or lipoprotein(a), which carry additional information. It also does not tell you what your target should be.
Lipid targets are clinical decisions. They depend on a person's overall risk, existing conditions, medicines, and the guideline being used. The calculator does not assign a target, a category, or a risk level. Use the target or range printed on the report and the plan agreed with a clinician.
Limitations
- High triglycerides. The equation is less reliable when triglycerides are high, and many labs use a direct measurement or another equation in that situation.
- Non-fasting samples. Triglycerides can be higher after food, which affects the calculation.
- Calculated vs measured. A direct LDL assay and a calculated LDL can differ.
- Other lipid markers. The equation does not account for apolipoprotein B, lipoprotein(a), or the size and number of LDL particles.
- Input errors. The result inherits any error in the three values entered, and a unit mismatch can produce a wrong number.
What this page is not
This calculator is a calculation from a published equation. It is not a diagnosis, a target, a treatment recommendation, or medical advice. It does not replace the LDL value, range, or comment on your report. Verify the inputs against the original report and discuss the result with a qualified professional.