Most "LDL" results are calculated, not measured. Enter your total cholesterol, HDL and triglycerides to see your LDL from both the classic Friedewald equation and the newer NIH (Sampson) equation, in mg/dL and mmol/L.
General information, not medical advice
This tool is for education and doesn't diagnose or treat anything. Lab methods and targets vary, and your own targets depend on your overall heart risk, so go through your results with your doctor or another qualified health professional.
The two equations
Friedewald (1972)
LDL = total cholesterol − HDL − triglycerides ÷ 5 (all in mg/dL)
Friedewald estimates the cholesterol carried in VLDL particles as triglycerides ÷ 5, and subtracts it along with HDL. In mmol/L the divisor is about 2.2. (This calculator converts to mg/dL first, which works out as ÷ 2.18.) It's simple, but the fixed ratio breaks down when triglycerides are high or LDL is low, and it shouldn't be used when triglycerides are above 400 mg/dL (4.5 mmol/L).
NIH / Sampson (2020)
LDL = TC/0.948 − HDL/0.971 − (TG/8.56 + TG × non-HDL/2140 − TG²/16100) − 9.44 (all in mg/dL)
Researchers at the US National Institutes of Health derived this equation from more than 8,000 patients whose LDL was measured with the reference method (beta-quantification). Instead of a fixed ÷ 5, the VLDL term adjusts for both triglycerides and non-HDL cholesterol. In the original study it estimated LDL for triglycerides up to 800 mg/dL as accurately as Friedewald does below 400 mg/dL.
The 2026 ACC/AHA dyslipidemia guideline recommends the Martin/Hopkins or Sampson equations over Friedewald. Martin/Hopkins uses a 180-cell lookup table rather than a formula, so it isn't included here. At normal triglyceride levels, all three give similar answers.
Worked example
Total cholesterol 200 mg/dL (5.17 mmol/L), HDL 50 mg/dL (1.29 mmol/L), triglycerides 150 mg/dL (1.69 mmol/L):
- Friedewald: 200 − 50 − 150 ÷ 5 = 120 mg/dL (3.10 mmol/L)
- Sampson: 210.97 − 51.49 − (17.52 + 10.51 − 1.40) − 9.44 = 123 mg/dL (3.19 mmol/L)
- Non-HDL: 200 − 50 = 150 mg/dL (3.88 mmol/L)
With triglycerides at 500 mg/dL instead (total 250, HDL 35), Friedewald gives 115 mg/dL and Sampson 125 mg/dL. That gap is why Friedewald isn't used above 400.
What your LDL result means
| LDL (mg/dL) | LDL (mmol/L) | Category |
|---|---|---|
| Under 100 | Under 2.6 | Optimal for most adults |
| 100–129 | 2.6–3.3 | Near optimal |
| 130–159 | 3.4–4.1 | Borderline high |
| 160–189 | 4.1–4.9 | High |
| 190 or more | 4.9 or more | Very high (ask about inherited high cholesterol) |
These are the general US categories. Treatment goals depend on your overall risk: people with heart disease or diabetes are often aimed below 70 mg/dL (1.8 mmol/L) or 55 mg/dL (1.4 mmol/L). In the UK, NICE sets treatment goals using non-HDL cholesterol, plus LDL for people who already have heart disease. For more, see how to read your cholesterol test results.
Sources
- Sampson M, 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.
- Blumenthal RS, et al. 2026 ACC/AHA Guideline on the Management of Dyslipidemia. JACC. 2026
- NICE NG238: Cardiovascular disease: risk assessment and reduction, including lipid modification
- MedlinePlus: Cholesterol levels, what you need to know
Frequently asked questions
How is LDL cholesterol calculated?
Most labs don't measure LDL directly. They measure total cholesterol, HDL and triglycerides, then estimate LDL with an equation. The oldest is the Friedewald equation: LDL = total cholesterol − HDL − triglycerides ÷ 5 (in mg/dL). Newer equations, such as the NIH (Sampson) and Martin/Hopkins equations, are more accurate when triglycerides are high or LDL is low.
What is the Sampson (NIH) equation?
An LDL equation published by Sampson and colleagues at the US National Institutes of Health in 2020. In mg/dL: LDL = TC/0.948 − HDL/0.971 − (TG/8.56 + TG × non-HDL/2140 − TG²/16100) − 9.44. It was developed against the reference ultracentrifugation method and works for triglycerides up to 800 mg/dL (9.0 mmol/L).
Can LDL be calculated if triglycerides are over 400?
Not with the Friedewald equation, which becomes unreliable above 400 mg/dL (4.5 mmol/L). The Sampson equation was validated up to 800 mg/dL (9.0 mmol/L). Above that, ask for a direct LDL measurement, and look at non-HDL cholesterol, which doesn't need an equation.
Why is my lab's LDL different from this calculator?
Your lab may use a different equation (many use Friedewald or Martin/Hopkins), measure LDL directly, or round the inputs differently. Differences of a few mg/dL (around 0.1 mmol/L) are normal. Larger gaps usually mean high triglycerides or a low LDL, where the equations disagree most.
Which LDL equation is the most accurate?
At normal triglyceride levels, the equations give similar results. When triglycerides are high or LDL is below 70 mg/dL (1.8 mmol/L), Friedewald tends to underestimate LDL, and the Sampson and Martin/Hopkins equations are closer to measured values. The 2026 ACC/AHA cholesterol guideline prefers Martin/Hopkins or Sampson over Friedewald.
Do I need to fast before a cholesterol test?
Usually not. Non-fasting tests are fine for most people. Current US guidance suggests a fasting test if a non-fasting triglyceride result is 400 mg/dL (4.5 mmol/L) or higher, because eating mainly raises triglycerides.
Track this over time in Heart Tracker
One LDL result is a snapshot. Heart Tracker logs every lipid panel in mg/dL or mmol/L, charts your LDL, HDL, non-HDL and triglycerides over time, and shows what you were eating between tests.
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