Friedewald is not valid above 400 mg/dL, which is 4.5 mmol/L.
The equation, and where it comes from
LDL = total cholesterol - HDL - (triglycerides / 5)
Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18(6):499-502.
How to read the result
The bands shown are the ATP III descriptive cut-points for LDL in mg/dL. What counts as an acceptable LDL for a given person depends on their overall cardiovascular risk, not on the number alone.
Your patient's numbers never leave this device
The ldl cholesterol arithmetic runs in JavaScript inside your own browser. There is no server call when you type, nothing is written to a database, nothing is logged, and no account is involved. Once the page has loaded you can disconnect from the network and it still works.
That matters more here than on an ordinary calculator. Values entered on a hospital workstation come off a real chart, and this tool deliberately does not remember them: close the tab and they are gone, including for the next person who uses that machine.
Frequently asked questions
- What is the Friedewald equation?
- LDL = total cholesterol - HDL - (triglycerides / 5), with every value in mg/dL. The triglycerides-over-five term is an estimate of VLDL cholesterol, which rests on the assumption that VLDL carries triglyceride and cholesterol in a roughly fixed 5:1 ratio.
- Why does Friedewald stop working above 400 mg/dL triglycerides?
- The fixed 5:1 ratio behind the VLDL term breaks down as triglycerides rise, so the equation increasingly underestimates LDL. The 1972 paper restricted it to samples below 400 mg/dL, and this calculator shows a warning past that point. A directly measured LDL is the answer there.
- What is non-HDL cholesterol and why is it shown?
- Non-HDL is total cholesterol minus HDL, so it captures every atherogenic particle rather than LDL alone. It needs no assumption about VLDL, which makes it more dependable than Friedewald LDL when triglycerides are high, and it is increasingly used as a risk target in its own right.
- Does the sample need to be fasting?
- Friedewald is sensitive to triglycerides, and triglycerides rise after eating, so the equation was built around fasting samples. Many current guidelines accept non-fasting lipids for screening, but if a non-fasting triglyceride is high the estimated LDL from this equation should be treated with caution.
- Can I enter values in mmol/L?
- Yes. Switch the unit on each field and every value is converted to mg/dL before the equation runs, which is why the triglyceride term is always divided by 5 rather than the 2.2 you would use working natively in mmol/L. The result is reported in mg/dL: multiply it by 0.02586 to read it back in mmol/L.