Heart & metabolic risk
LDL cholesterol calculator (NIH and Friedewald)
Estimate your LDL cholesterol from total cholesterol, HDL and triglycerides with the NIH (Sampson) equation, compare it with the older Friedewald formula, and see where the result sits in the standard LDL categories.
Enter your values above to see your result and what it means.
What is calculated LDL (LDL Chol Calc NIH)?
On many lab reports, LDL cholesterol is calculated from three measured values: total cholesterol, HDL cholesterol and triglycerides. Direct LDL tests exist, but they cost more, so calculating LDL remains common practice. US labs increasingly report the NIH equation, published by Sampson and colleagues at the NIH Clinical Center in 2020. If your report shows a line such as "LDL Chol Calc (NIH)", the NIH in the name refers to this equation, the same one this calculator uses for its main result.
Normal LDL cholesterol levels
The calculator places your result in the NCEP ATP III categories from the US National Heart, Lung, and Blood Institute: below 100 mg/dL is optimal, 100 to 129 near or above optimal, 130 to 159 borderline high, 160 to 189 high, and 190 or more very high. These categories describe the number. The LDL goal that applies to you personally depends on your overall cardiovascular risk, so two people with the same LDL can be advised differently.
| LDL cholesterol (mg/dL) | Category |
|---|---|
| Below 100 | Optimal |
| 100 to 129 | Near or above optimal |
| 130 to 159 | Borderline high |
| 160 to 189 | High |
| 190 or more | Very high |
LDL calculation: NIH equation vs Friedewald
The Friedewald formula (1972) is LDL = total cholesterol - HDL - triglycerides/5. The triglycerides/5 term estimates the cholesterol carried in VLDL, and it is the main source of error, because the ratio of cholesterol to triglycerides in VLDL varies from person to person. The NIH equation (Sampson 2020) replaces that fixed term with one that adjusts for triglycerides and non-HDL cholesterol: LDL = TC/0.948 - HDL/0.971 - (TG/8.56 + TG x non-HDL/2140 - TG²/16100) - 9.44. Measured against the reference method, its typical error was 15.2 mg/dL compared with 32 mg/dL for Friedewald, and it works up to triglycerides of 800 mg/dL about as well as Friedewald does below 400.
| NIH equation (Sampson 2020) | Friedewald (1972) | |
|---|---|---|
| Inputs | Total cholesterol, HDL, triglycerides | Total cholesterol, HDL, triglycerides |
| Triglyceride limit | Up to 800 mg/dL | Up to 400 mg/dL |
| Typical error vs reference method (RMSE) | 15.2 mg/dL | 32 mg/dL |
| At low LDL levels | Fewer misclassifications | Tends to read too low |
Non-fasting tests and high triglycerides
Most guidelines now accept a non-fasting sample for an initial lipid check. Sampson and colleagues found the NIH equation unaffected by fasting state, which matters because triglycerides feed into every LDL formula. When triglycerides are very high, labs may decline to report a calculated LDL or may measure it directly instead. This calculator hides the Friedewald value above 400 mg/dL and gives no result above 800 mg/dL, the upper limit of the range the NIH equation was tested on. Labs differ in which formula they print, so check the name on your report before comparing numbers.
Frequently asked questions
What does "LDL Chol Calc (NIH)" mean on my lab report?
It is your LDL cholesterol calculated with the NIH equation (Sampson 2020) from your total cholesterol, HDL and triglycerides. "Calc" means the value was calculated from those measurements. The main result of this calculator uses the same equation.
What is the Friedewald equation?
The Friedewald equation, from 1972, estimates LDL as total cholesterol minus HDL minus triglycerides divided by 5 (all in mg/dL). It was the standard for decades. It becomes unreliable when triglycerides are above 400 mg/dL and tends to underestimate LDL when LDL is low.
Is calculated LDL accurate if I did not fast?
Most guidelines now accept non-fasting lipid tests for a first check, and the study behind the NIH equation found it unaffected by fasting state. If your lab or clinician asked you to fast, follow that instruction.
What is a normal calculated LDL?
In the NCEP ATP III categories, below 100 mg/dL is optimal and 100 to 129 is near or above optimal. From 130 upward the categories are borderline high, high and very high. Your personal goal depends on your overall cardiovascular risk, which a clinician assesses.
Why does the calculator not show Friedewald for my result?
Friedewald is hidden when triglycerides are above 400 mg/dL, because its fixed triglycerides/5 term no longer estimates VLDL cholesterol reliably at that level. The NIH equation is shown up to 800 mg/dL.
Sources
- Sampson M, Ling C, Sun Q, et al. A new equation for calculation of low-density lipoprotein cholesterol in patients with normolipidemia and/or hypertriglyceridemia. JAMA Cardiol. 2020;5(5):540-548.
- 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.
- National Heart, Lung, and Blood Institute. ATP III At-a-Glance: Quick Desk Reference.