What this calculator does
Most lipid panels do not measure LDL directly. They measure total cholesterol, HDL and triglycerides, and calculate LDL from those three using the Friedewald equation, which has been standard since 1972.
The estimate depends on triglycerides, which is where it breaks down. The same total and HDL give an LDL of 130 mg/dL at 100 triglycerides but 90 at 300, and above about 400 the equation stops being reliable at all.
The formula
Subtract HDL and one fifth of the triglycerides from total cholesterol. The triglyceride term approximates the cholesterol carried in VLDL particles.
| Term | Meaning |
|---|---|
| Friedewald equation | The standard calculation for LDL from a routine panel. |
| VLDL | Very low density lipoprotein, estimated here as triglycerides divided by five. |
| Direct LDL | A separate laboratory measurement, needed when the equation is not valid. |
The inputs explained
| Field | What to enter |
|---|---|
| Total cholesterol (mg/dL) | Total cholesterol in mg/dL. |
| HDL cholesterol (mg/dL) | HDL cholesterol in mg/dL. |
| Triglycerides (mg/dL) | Triglycerides in mg/dL. The equation is unreliable above about 400. |
When to use it
Checking a lipid panel
Seeing how the three measured values combine explains what the LDL line on a report actually is.
Understanding why LDL moved
A change in triglycerides alone shifts calculated LDL without any change in LDL particles.
Knowing when a direct test is needed
High triglycerides invalidate the estimate, and a direct measurement is required instead.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How do triglycerides affect the estimate?
The same total and HDL at three triglyceride levels.
| Triglycerides | LDL cholesterol | Note |
|---|---|---|
| 100 mg/dL | 130 mg/dL | Valid for triglycerides under about 400 mg/dL. |
| 150 mg/dL | 120 mg/dL | Valid for triglycerides under about 400 mg/dL. |
| 300 mg/dL | 90 mg/dL | Valid for triglycerides under about 400 mg/dL. |
Questions
Why does the equation fail at high triglycerides?
Because the VLDL estimate assumes a fixed ratio of triglycerides to cholesterol in those particles. That ratio shifts as triglycerides rise, so above roughly 400 mg/dL the approximation breaks down and a direct LDL measurement is needed.
Does fasting matter?
It affects triglycerides, which feed into the calculation, so non-fasting samples can produce a different calculated LDL. Guidance on fasting has changed in recent years and varies, so follow the instruction given with your test.
Are there better equations?
Yes. The Martin-Hopkins and Sampson equations use variable rather than fixed factors and perform better at low LDL and high triglycerides. Many laboratories have moved to them, so a reported LDL may not match this calculation.
What LDL level should I be aiming for?
That depends on your overall cardiovascular risk, not on the number alone. Targets differ considerably between people with and without existing heart disease, diabetes or other risk factors, and should be set with your clinician.
For a single risk ratio from the same panel, see the cholesterol ratio calculator. For average glucose from A1C, see the estimated average glucose calculator.