LDL Calculator Formula: How It Works

This calculator estimates your LDL (low-density lipoprotein) cholesterol using the Friedewald equation, based on your total cholesterol, HDL cholesterol, and triglycerides. You enter those three values in mg/dL, and you get an estimated LDL level in mg/dL. The formula is a standard clinical tool, but it has important limitations you should understand before relying on it.

Formula

The Friedewald equation estimates LDL cholesterol as:

LDL = Total Cholesterol − HDL Cholesterol − (Triglycerides / 5)

All values are in milligrams per deciliter (mg/dL). The term (Triglycerides / 5) estimates VLDL (very-low-density lipoprotein) cholesterol, because VLDL carries most of the triglyceride in the blood and its cholesterol content is roughly one-fifth of the triglyceride concentration.

For example, if your total cholesterol is 200 mg/dL, HDL is 50 mg/dL, and triglycerides are 150 mg/dL, the equation gives:

LDL = 200 − 50 − (150/5) = 200 − 50 − 30 = 120 mg/dL

Worked Example

Using the default values from the calculator above:

• Total cholesterol = 200 mg/dL
• HDL cholesterol = 50 mg/dL
• Triglycerides = 150 mg/dL

Step 1: Divide triglycerides by 5 → 150 / 5 = 30 mg/dL (this is the estimated VLDL).

Step 2: Subtract HDL and VLDL from total cholesterol → 200 − 50 − 30 = 120 mg/dL.

The calculator shows an estimated LDL of 120 mg/dL, which matches the manual calculation.

When to Use This Formula

The Friedewald equation is used when a direct LDL measurement is not available or not ordered. It is the most common method in routine lipid panels because it is inexpensive and requires no additional fasting beyond the standard lipid test. Doctors often use it to assess cardiovascular risk and decide whether to start or adjust cholesterol-lowering treatment.

It is most accurate when your blood sample is taken after a 9–12 hour fast, because eating raises triglycerides temporarily and skews the estimate. If you have not fasted, the calculated LDL may be lower than your true fasting level.

How to Read Your Result

Estimated LDL is interpreted with clinical context, not as a standalone number. General categories for LDL (in mg/dL) are:

• Below 100: optimal
• 100–129: near optimal
• 130–159: borderline high
• 160–189: high
• 190 and above: very high

However, your target LDL depends on your personal risk factors, such as age, smoking, blood pressure, diabetes, and family history. A level that is acceptable for one person may be too high for someone with existing heart disease. Always discuss your numbers with a healthcare provider.

Common Mistakes and Limitations

The Friedewald equation has well-known limitations:

• High triglycerides: The formula becomes inaccurate when triglycerides exceed 400 mg/dL. The VLDL estimate (triglycerides/5) is less reliable at high levels, and the calculated LDL can be falsely low. In such cases, a direct LDL measurement is recommended.
• Non-fasting samples: Eating before the test raises triglycerides, which can lower the calculated LDL. Fasting for 9–12 hours is standard for accurate results.
• Unit confusion: The formula uses mg/dL. In countries that use mmol/L, the equation is different (LDL = TC − HDL − TG/2.2). If you enter mmol/L values into this calculator, the result will be wrong.
• Rounding: The formula is sensitive to rounding. For example, if your triglycerides are 149 mg/dL, the VLDL estimate is 29.8, and LDL = TC − HDL − 29.8. Rounding to whole numbers can change the LDL by 1 mg/dL, which is usually not clinically significant.

Alternatives to the Friedewald Equation

Because of its limitations, several alternatives exist:

• Direct LDL measurement: A blood test that measures LDL directly, using ultracentrifugation or homogeneous assays. It is more accurate, especially when triglycerides are high, but it is more expensive and not always covered by insurance.
• Martin-Hopkins equation: A newer formula that uses a more detailed factor for VLDL based on triglyceride and non-HDL categories. It is more accurate than Friedewald, particularly at higher triglyceride levels, but requires a table of factors.
• ApoB or LDL particle number: These tests measure the number of LDL particles, which may be a better predictor of risk than LDL cholesterol alone. They are not part of a standard lipid panel.

Your doctor will choose the most appropriate test based on your situation.

Frequently Asked Questions

Why is the formula LDL = TC − HDL − TG/5?

The equation comes from the observation that VLDL cholesterol is roughly one-fifth of the triglyceride concentration (in mg/dL). Since total cholesterol is the sum of HDL, LDL, and VLDL cholesterol, subtracting HDL and the estimated VLDL leaves an estimate of LDL. This relationship was derived from population data and works well for most people with normal triglyceride levels.

Can I use this calculator if my triglycerides are over 400 mg/dL?

No. The Friedewald equation is not reliable when triglycerides exceed 400 mg/dL. The VLDL estimate becomes inaccurate, and the calculated LDL can be significantly wrong. In that case, ask your doctor for a direct LDL measurement or an alternative formula like Martin-Hopkins.

Do I need to fast before getting my lipid panel?

Yes, for the Friedewald equation to be accurate, you should fast for 9–12 hours before the blood draw. Eating raises triglycerides, which lowers the calculated LDL. Some newer guidelines allow non-fasting tests, but the Friedewald formula is still more accurate with fasting values.

What is the difference between LDL and non-HDL cholesterol?

Non-HDL cholesterol is simply total cholesterol minus HDL. It includes LDL plus VLDL and other atherogenic particles. Non-HDL is often used as a secondary target because it does not require fasting and is less affected by triglyceride levels. Some doctors prefer it over LDL for risk assessment.

Is the Friedewald formula still used today?

Yes, it remains the most common method for estimating LDL in routine lipid panels because it is inexpensive and works well for most people. However, many labs now use the Martin-Hopkins equation or direct LDL measurement when triglycerides are high. The Friedewald formula is still taught and used widely, but it is not the only option.

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in tc | Total Cholesterol | mg/dL | 200 | 0
in hdl | HDL Cholesterol | mg/dL | 50 | 0
in tg | Triglycerides | mg/dL | 150 | 0
out ldl | Estimated LDL | mg/dL | tc - hdl - (tg / 5) | 0
out vldl | VLDL (estimated) | mg/dL | tg / 5 | 0
out non_hdl | Non-HDL Cholesterol | mg/dL | tc - hdl | 0