LDL Calculator

LDL Calculator for Endocrinology. The output is estimated cholesterol in the LDL fraction, not direct measurement, a diagnosis or a prescribed goal. The component does not label isolated LDL values as a person's overall cardiovascular risk.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

Friedewald LDL-C = total cholesterol - HDL-C - triglycerides/5 with all concentrations first expressed in mg/dL. The output is converted to mmol/L using 0.0259. This implementation uses the same mass-based equation in both entry modes rather than switching to the rounded SI divisor 2.2.

When to use this calculator

For historical equation learning and checking a compatible lipid profile. It is not the preferred contemporary LDL estimation method: the 2026 US guideline favors Martin/Hopkins or Sampson/NIH, neither of which is implemented here.

Inputs used

  • Total cholesterol
  • HDL cholesterol
  • Triglycerides
  • Friedewald specimen assumptions; concentrations in mmol/L or mg/dL

Clinical interpretation

The output is estimated cholesterol in the LDL fraction, not direct measurement, a diagnosis or a prescribed goal. The component does not label isolated LDL values as a person's overall cardiovascular risk.

Worked example

Total 200, HDL 50 and triglycerides 150 mg/dL give 200 - 50 - 30 = 120 mg/dL, or 3.108 mmol/L. Triglycerides 399.9 remain below the method cutoff; at exactly 400 mg/dL (4.52 mmol/L with this converter), no LDL estimate is returned.

Limitations and safety notes

The estimate becomes less reliable with increasing triglycerides or low LDL. It is withheld for negative calculated LDL, inconsistent total/HDL, unconfirmed specimen assumptions or triglycerides at/above 400 mg/dL. This interface restricts use to fasting samples without known chylomicronemia/type III dyslipoproteinemia; that restriction is not a general instruction that all lipid testing requires fasting.

Frequently asked questions

Why does 4.5 mmol/L differ slightly from the exact cutoff?

4.5 is a commonly rounded equivalent. With the tool's 0.0113 triglyceride conversion, 400 mg/dL equals 4.52 mmol/L.

Must an unavailable Friedewald result be replaced by a direct assay?

Not automatically. Method selection belongs to the laboratory and clinician; newer validated equations can be appropriate.

References

  • Friedewald WT et al. Clinical Chemistry 1972;18:499-502. https://pubmed.ncbi.nlm.nih.gov/4337382/
  • AHA/ACC et al. Dyslipidemia guideline 2026: preferred estimation methods and limitations of Friedewald. https://doi.org/10.1161/CIR.0000000000001423

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

Related reviewed calculators