LDL Cholesterol Calculator
Your total cholesterol from a fasting lipid panel
High-density lipoprotein — the 'good' cholesterol
Blood fat level — Friedewald formula invalid above 400 mg/dL
Select your risk profile to see your personalized LDL target
Enter Your Cholesterol Values
Input your total cholesterol, HDL, and triglycerides to calculate your LDL cholesterol using multiple formulas.
Understanding LDL Cholesterol
LDL cholesterol is the primary lipid marker used to assess cardiovascular disease risk. Understanding how it is calculated, what your result means, and how to interpret it in context is essential for managing heart health.
What Is LDL Cholesterol?
LDL, or low-density lipoprotein, is a type of lipoprotein particle that carries cholesterol from the liver to cells throughout the body. When LDL levels are too high, excess cholesterol can deposit in artery walls, forming plaques that narrow vessels and restrict blood flow. This process — atherosclerosis — underlies most heart attacks and strokes. LDL is called 'bad' cholesterol not because it is inherently harmful at normal levels, but because chronically elevated LDL is one of the strongest modifiable risk factors for cardiovascular disease. The AHA/ACC 2018 guidelines emphasize LDL-C as the primary target for lipid-lowering therapy. Unlike HDL ('good' cholesterol), which carries cholesterol back to the liver for disposal, LDL drives cholesterol into peripheral tissues including arterial walls.
How Is LDL Calculated?
Clinical labs typically calculate LDL from a standard lipid panel rather than measuring it directly. The Friedewald equation (LDL = TC - HDL - TG/5) has been the standard since 1972. However, it assumes a fixed 5:1 ratio between triglycerides and VLDL cholesterol, which becomes inaccurate at high or low triglyceride extremes. The Martin-Hopkins equation replaces the fixed divisor of 5 with an adjustable factor (D) determined from a validated 174-cell lookup table based on non-HDL cholesterol and triglyceride strata. Published in 2013 and validated in 1.3 million patients, it is now recommended by the ACC/AHA as the preferred calculation method. The Sampson NIH equation (2020) uses a nonlinear quadratic formula — LDL = (TC/0.948) - (HDL/0.971) - (TG/8.56 + TG x non-HDL/2140 - TG^2/16100) - 9.44 — which is accurate across the full range of triglycerides up to 800 mg/dL.
Why LDL Level Matters for Heart Health
Each 1 mmol/L (approximately 39 mg/dL) reduction in LDL cholesterol reduces the risk of major cardiovascular events by approximately 22%, according to large meta-analyses of statin trials. This relationship holds across a wide range of baseline LDL levels and across different patient populations. For patients with established cardiovascular disease, reducing LDL below 70 mg/dL can halt and even partially reverse plaque buildup. For very high-risk patients after a recent acute coronary syndrome, guidelines now recommend targets below 55 mg/dL. Non-HDL cholesterol — which includes LDL plus VLDL and other atherogenic lipoproteins — provides additional predictive value beyond LDL alone and is particularly useful in patients with elevated triglycerides where LDL calculation may be less accurate. The TC-to-HDL ratio is another useful cardiovascular risk marker, with values below 3.5 considered optimal.
Limitations of Calculated LDL
Calculated LDL values are estimates based on mathematical formulas, not direct measurements. The Friedewald equation is invalid when triglycerides exceed 400 mg/dL, when the patient was not fasting before the blood draw, or in rare lipid disorders such as type I or type III hyperlipoproteinemia. Even the Martin-Hopkins and Sampson equations have higher uncertainty at extreme triglyceride levels. All calculated LDL values have inherent measurement error of approximately 10-15 mg/dL in ideal conditions. For patients near important treatment thresholds — particularly those where adding or stopping a medication is being considered — direct LDL-C measurement may be warranted. Discuss any questions about your specific results with your physician, especially if you have high triglycerides, a known lipid disorder, or are making treatment decisions based on borderline LDL values.
How to Use This LDL Calculator
Enter Your Lipid Panel Values
Type in your Total Cholesterol, HDL Cholesterol, and Triglycerides from your most recent fasting blood test. Use the unit toggle to switch between mg/dL and mmol/L to match your lab report. All three values are required to calculate LDL.
Choose Your Calculation Formula
Select Friedewald for standard clinical use (valid when TG is below 400 mg/dL), Martin-Hopkins for better accuracy at moderate-to-high triglycerides, Sampson NIH for hypertriglyceridemia (TG up to 800 mg/dL), or Compare All to see results from all three formulas simultaneously. The calculator will auto-recommend the best formula based on your triglyceride level.
Review Your LDL Result and Classification
Your calculated LDL is displayed prominently with the AHA/ACC classification — Optimal, Near Optimal, Borderline High, High, or Very High. You will also see Non-HDL Cholesterol, VLDL estimate, TC-to-HDL ratio, LDL-to-HDL ratio, and a step-by-step breakdown of the formula applied to your exact values.
Set Your Risk Level for a Personalized Target
Optionally select your cardiovascular risk category — Very High, High, Moderate, or Lower Risk — to see your personalized LDL treatment target per AHA/ACC guidelines. The results section will show exactly how far your current LDL is above or below your recommended goal, helping you track progress over time.
Frequently Asked Questions
What is the difference between Friedewald, Martin-Hopkins, and Sampson equations?
The Friedewald equation (1972) is the original LDL calculation formula: LDL = TC - HDL - (TG/5). It assumes a fixed ratio between triglycerides and VLDL cholesterol, which works well for most patients but becomes inaccurate at high or low triglyceride extremes. The Martin-Hopkins equation (2013) replaces the fixed divisor with an adjustable factor (D) determined from a validated lookup table of 174 triglyceride and non-HDL strata. Validated in 1.3 million patients, it correctly classifies 89.6% of patients versus 79.9% for Friedewald. The Sampson NIH equation (2020) is a nonlinear quadratic formula that achieves the highest accuracy and is valid for triglycerides up to 800 mg/dL, making it ideal for patients with hypertriglyceridemia.
Why is the Friedewald formula invalid when triglycerides are above 400 mg/dL?
The Friedewald equation estimates VLDL cholesterol as triglycerides divided by 5, based on an assumed fixed 5:1 TG-to-VLDL ratio. At triglyceride levels above 400 mg/dL, this ratio breaks down significantly. Very high triglycerides are associated with the presence of chylomicrons and chylomicron remnants, which change the lipoprotein composition in ways the fixed-ratio formula cannot account for. Using Friedewald at high triglycerides typically results in a falsely low or even negative LDL value. In these situations, Martin-Hopkins or Sampson formulas should be used, or direct LDL-C measurement should be ordered by a physician.
What LDL level should I aim for?
AHA/ACC guidelines define LDL targets based on cardiovascular risk. For very high-risk patients — those with established cardiovascular disease, recent acute coronary syndrome, or multiple high-risk conditions — the target is below 55 mg/dL (1.4 mmol/L). For high-risk patients with coronary artery disease, diabetes, or severe chronic kidney disease, the goal is below 70 mg/dL (1.8 mmol/L). For moderate-risk patients with two or more major risk factors, the target is below 100 mg/dL (2.6 mmol/L). For lower-risk individuals with zero or one risk factor, below 130 mg/dL (3.4 mmol/L) is generally recommended. These are guidelines — your physician will set your individual target based on your complete risk profile, medical history, and other factors.
What is Non-HDL Cholesterol and why does it matter?
Non-HDL Cholesterol is calculated as Total Cholesterol minus HDL Cholesterol. It represents all atherogenic (artery-clogging) lipoproteins in the blood, including LDL, VLDL, IDL, and lipoprotein(a). Because it captures a broader range of cardiovascular risk particles than LDL alone, non-HDL is considered a superior predictor of cardiovascular events — particularly in patients with elevated triglycerides where LDL calculation is less accurate. The AHA/ACC guidelines now recommend non-HDL as an important secondary risk marker. Optimal non-HDL is below 130 mg/dL. Non-HDL targets are typically set 30 mg/dL higher than LDL targets for the same risk category.
What does the TC-to-HDL ratio mean?
The Total Cholesterol to HDL ratio (TC:HDL ratio) is a simple cardiovascular risk indicator that compares your total cholesterol to your protective HDL cholesterol. A lower ratio is better, as it indicates more of your cholesterol is the protective HDL type. An optimal ratio is below 3.5:1 for both men and women. A ratio of 5.0 for men or 4.5 for women indicates average cardiovascular risk. Values above 6 are considered elevated risk. The TC:HDL ratio is sometimes used in risk calculators when LDL data is unavailable, and it provides useful additional information even when LDL is known. However, like all lipid metrics, it should be interpreted in the context of a complete cardiovascular risk assessment by a healthcare professional.
Do I need to fast before a cholesterol test?
The Friedewald equation specifically requires a fasting blood specimen — typically 9 to 12 hours without food or caloric beverages. This is because eating raises triglycerides temporarily, which directly affects the Friedewald LDL calculation since triglycerides are divided by 5 to estimate VLDL. Non-fasting triglycerides can be 20-50 mg/dL higher than fasting levels, leading to LDL underestimation. The Martin-Hopkins and Sampson equations are somewhat more robust to non-fasting specimens because they use adjustable factors, but fasting is still preferred for the most accurate results across all formulas. Your laboratory results will typically indicate whether the specimen was fasting or non-fasting.