LDL Calculator — Friedewald Formula

Q: What is the Friedewald formula?

LDL = Total cholesterol − HDL − (Triglycerides / 5), all in mg/dL. It estimates LDL cholesterol from a standard lipid panel without a direct LDL measurement.

Q: Why divide triglycerides by 5?

Dividing triglycerides by 5 approximates VLDL cholesterol, since VLDL particles typically carry about one-fifth as much cholesterol as triglyceride by mass. Subtracting that estimated VLDL, along with HDL, from total cholesterol leaves LDL.

Q: When is the Friedewald formula invalid?

When triglycerides are 400 mg/dL (about 4.5 mmol/L) or higher. Above that level the TG/5 approximation of VLDL breaks down, and a directly measured (not calculated) LDL is needed.

Q: What is the mmol/L version of the formula?

LDL = Total cholesterol − HDL − (Triglycerides / 2.2), all in mmol/L. This calculator's unit toggle switches your inputs and result between mg/dL and mmol/L automatically.

Q: What units does this calculator use?

Total cholesterol, HDL, triglycerides, and the resulting LDL can all be entered and displayed in either mg/dL (US convention) or mmol/L (used in many other countries) — toggle the unit buttons above the inputs.

Q: Is this medical advice?

No. This calculator is for informational and educational purposes only. Always use your lab-reported LDL when available, and discuss your cholesterol results with a qualified healthcare professional.

Units	Formula
mg/dL	LDL = TC − HDL − (TG ÷ 5)
mmol/L	LDL = TC − HDL − (TG ÷ 2.2)

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Walk-through

How to Use This Calculator

4 steps

1

Enter your lipid panel

Enter total cholesterol, HDL cholesterol, and triglycerides from a recent lipid panel, ideally a fasting blood draw. Use the mg/dL or mmol/L toggle to match how your lab reported the results — the calculator converts internally and displays your answer in the unit you selected.

2

Read your estimated LDL and risk tier

The headline number is your LDL estimated by the Friedewald formula. Below it, the stat grid shows the estimated VLDL used in the calculation and whether the formula is valid for your triglyceride level. The interpretation panel names your ATP III / ACC-AHA risk tier — Optimal, Near optimal, Borderline high, High, or Very high.

3

Check validity if your triglycerides are high

Open the Validity Check tab to see the formula in both unit systems and a live readout of whether your current triglyceride value falls above the 400 mg/dL (about 4.5 mmol/L) threshold where the Friedewald estimate becomes unreliable.

4

Compare two lab panels

The Risk Tier tab includes a side-by-side comparison — enter two panels (for example, last visit vs. this visit) to see how the estimated LDL and risk tier shift between them.

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Reference

Formula & Methodology

2 formulas

Friedewald formula — mg/dL

LDL = TC − HDL − (TG ÷ 5)

Total cholesterol (TC), HDL, and triglycerides (TG) are all in mg/dL. Dividing triglycerides by 5 approximates VLDL cholesterol; subtracting that estimated VLDL and HDL from total cholesterol leaves LDL. Valid only when TG is below 400 mg/dL. Source: Friedewald WT, Levy RI, Fredrickson DS. Clin Chem. 1972;18(6):499-502.

Friedewald formula — mmol/L

LDL = TC − HDL − (TG ÷ 2.2)

The same formula in mmol/L, the unit convention used in Canada, the UK, and much of Europe. TG is divided by 2.2 instead of 5 because triglycerides and cholesterol have different molar masses; the two forms of the formula agree with each other to within normal rounding once unit conversion is accounted for. Valid only when TG is below about 4.5 mmol/L.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Team · Updated 2026-07-23 · 3 sources

Editorial accountability

Author: Calculover Editorial Team - Editor

Owner: Calculover Editorial Team - Editorial owner

Reviewer: Calculover Editorial Team - Clinical content reviewer

Last reviewed: 2026-07-23

Last verified: 2026-07-23

Data effective: 2026-07-23

Methodology

The LDL Calculator applies the Friedewald equation (Friedewald WT, Levy RI, Fredrickson DS. Clin Chem. 1972;18(6):499-502): LDL = TC − HDL − (TG ÷ 5) in mg/dL, or the equivalent LDL = TC − HDL − (TG ÷ 2.2) in mmol/L. VLDL cholesterol is estimated as TG ÷ 5 (mg/dL), based on the typical triglyceride-to-cholesterol ratio in VLDL particles. The formula is only applied when triglycerides are below 400 mg/dL (about 4.5 mmol/L); at or above that threshold the calculator flags the result as invalid rather than reporting a misleadingly precise number. The resulting LDL is classified into five risk tiers using the cut points from the National Cholesterol Education Program's Adult Treatment Panel III (ATP III), carried forward in the 2018 ACC/AHA Guideline on the Management of Blood Cholesterol: Optimal (<100 mg/dL), Near optimal (100-129), Borderline high (130-159), High (160-189), Very high (≥190).

Assumption: Total cholesterol, HDL, and triglycerides come from the same blood draw, ideally a fasting sample, and are entered in a consistent unit system.

Assumption: Triglycerides are below 400 mg/dL (about 4.5 mmol/L) — the range in which the Friedewald formula's VLDL approximation is considered reliable.

Assumption: The user wants an estimate consistent with how most clinical labs calculate LDL on a routine panel, not a substitute for a directly measured LDL.

Limitations & guidance

The Friedewald formula is an approximation, not a direct measurement. It systematically understates true LDL as triglycerides rise, and is not reliable at all once triglycerides reach 400 mg/dL or higher — the calculator flags this case rather than showing a number.

The formula assumes a fasting sample. A non-fasting draw can elevate triglycerides and introduce chylomicrons, both of which reduce the accuracy of the VLDL estimate even below the 400 mg/dL cutoff.

This calculator does not account for other conditions that affect LDL estimation accuracy, such as type III dysbetalipoproteinemia, and it does not replace direct LDL measurement, apolipoprotein B testing, or a clinician's full risk assessment.

Professional guidance: This calculator is for informational and educational purposes only. It is not medical advice and does not replace your lab-reported LDL or a qualified healthcare professional's interpretation of your cholesterol results. Do not make medical decisions based solely on its output.

Primary sources

Friedewald WT, Levy RI, Fredrickson DS. Estimation of the Concentration of Low-Density Lipoprotein Cholesterol in Plasma, Without Use of the Preparative Ultracentrifuge. Clinical Chemistry. 1972;18(6):499-502. - Clinical Chemistry

Grundy SM, et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol. - American College of Cardiology / American Heart Association

National Cholesterol Education Program. Third Report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). - National Heart, Lung, and Blood Institute

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Glossary

Key Terms Explained

7 terms

Friedewald formula An equation that estimates LDL cholesterol from a standard lipid panel — total cholesterol, HDL, and triglycerides — without requiring a direct LDL measurement. Published by Friedewald, Levy, and Fredrickson in 1972 and still the most widely used method for reporting LDL on routine lab panels.

LDL (low-density lipoprotein) cholesterol Often called "bad" cholesterol. LDL particles carry cholesterol into artery walls, where it can contribute to plaque buildup; higher LDL is associated with greater cardiovascular risk. This calculator estimates LDL rather than measuring it directly.

Total cholesterol (TC) The sum of all cholesterol carried in the blood — LDL, HDL, and VLDL cholesterol combined. Reported on every standard lipid panel and used as an input to the Friedewald formula.

HDL (high-density lipoprotein) cholesterol Often called "good" cholesterol. HDL particles help clear excess cholesterol from the bloodstream. In the Friedewald formula, HDL is subtracted directly (not estimated) from total cholesterol.

Triglycerides (TG) A type of fat carried mainly by VLDL particles in the blood. In the Friedewald formula, triglycerides divided by 5 (mg/dL) or 2.2 (mmol/L) approximates VLDL cholesterol — the piece of total cholesterol that is neither LDL nor HDL.

Formula validity range The Friedewald formula assumes a roughly constant ratio between triglyceride and cholesterol content in VLDL particles. That assumption holds reasonably well below 400 mg/dL (about 4.5 mmol/L) of triglycerides; above that, chylomicrons and other triglyceride-rich particles distort the ratio and the estimate becomes unreliable.

Risk tier The ATP III / 2018 ACC-AHA classification of an LDL value into one of five bands — Optimal, Near optimal, Borderline high, High, or Very high — used to contextualize cardiovascular risk and guide treatment discussions.

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Scenarios

Real-World Examples

3 worked examples

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Standard lipid panel

Typical case, mg/dL

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

VLDL is estimated as 150 ÷ 5 = 30 mg/dL. LDL = 200 − 50 − 30 = 120 mg/dL, which falls in the Near optimal band (100-129 mg/dL). Triglycerides of 150 mg/dL are well under the 400 mg/dL validity threshold, so this estimate is reliable.

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High-triglyceride panel

Formula invalid, mg/dL

Total cholesterol 220 mg/dL HDL 45 mg/dL Triglycerides 450 mg/dL

The arithmetic still runs — VLDL = 450 ÷ 5 = 90 mg/dL, LDL = 220 − 45 − 90 = 85 mg/dL — but because triglycerides (450 mg/dL) are at or above the 400 mg/dL threshold, the calculator flags this result as invalid. The TG/5 approximation breaks down at this level and would understate the true LDL; a directly measured LDL from the lab should be used instead.

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Unit toggle round-trip

mmol/L equivalent of the typical case

Total cholesterol 5.2 mmol/L HDL 1.3 mmol/L Triglycerides 1.7 mmol/L

Converting through mg/dL internally gives an LDL of about 3.12 mmol/L — the mmol/L equivalent of the 120 mg/dL result from the first example, and still in the Near optimal band. The mmol/L-native shorthand (5.2 − 1.3 − 1.7 ÷ 2.2 ≈ 3.13) agrees to within normal rounding. Use whichever unit system matches your lab report; the underlying LDL doesn't change.

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Deep Dive

Understanding the LDL Calculator (Friedewald Formula)

4 chapters · 4 min read

Most lipid panels report an LDL cholesterol value that was never directly measured — it was calculated from total cholesterol, HDL, and triglycerides using the Friedewald formula, published in 1972 and still the default method used by most clinical laboratories. This calculator reproduces that formula, explains when it can and can't be trusted, and shows where your result sits on the standard cardiovascular risk scale.

How the Friedewald formula works

The formula estimates LDL as total cholesterol minus HDL minus an estimate of VLDL cholesterol. VLDL isn't measured directly on a routine panel either — it's approximated as triglycerides divided by 5 (in mg/dL) or 2.2 (in mmol/L), based on the typical ratio of triglyceride to cholesterol content inside VLDL particles.

That means the Friedewald LDL is really a subtraction problem built on one direct measurement (total cholesterol), one direct measurement (HDL), and one approximation (VLDL, derived from triglycerides). It is fast, requires no extra lab work beyond a standard panel, and is accurate enough for the vast majority of patients — which is why it remains the default reporting method decades after publication.

Why high triglycerides break the formula

The TG ÷ 5 approximation of VLDL assumes a fairly stable ratio between triglyceride and cholesterol content across VLDL particles. That ratio holds up reasonably well under normal conditions, but it drifts as triglycerides climb — chylomicrons (which appear after a non-fasting draw or in some metabolic conditions) and triglyceride-rich VLDL remnants both carry proportionally less cholesterol per unit of triglyceride than the formula assumes.

Above roughly 400 mg/dL (about 4.5 mmol/L) of triglycerides, that drift becomes large enough that the calculated LDL meaningfully understates the true value. Laboratories typically suppress or flag the calculated LDL at this point and, where clinically needed, run a direct LDL measurement instead — a different lab method that doesn't rely on the triglyceride-based VLDL estimate.

LDL risk tiers explained

Once an LDL value is available — whether calculated or directly measured — it's classified using the same five-tier scale from the National Cholesterol Education Program's Adult Treatment Panel III (ATP III), carried forward into the 2018 ACC/AHA Guideline on the Management of Blood Cholesterol: Optimal (under 100 mg/dL), Near optimal (100-129), Borderline high (130-159), High (160-189), and Very high (190 and above).

These bands are a starting point for a conversation about cardiovascular risk, not a standalone verdict — the treatment threshold a clinician actually uses also depends on other risk factors: age, blood pressure, smoking status, diabetes, family history, and other lipid values like non-HDL cholesterol and Lp(a).

Limits and when to trust a direct measurement

This calculator is for informational and educational purposes only. It reproduces a well-established clinical formula, but it does not replace your lab's reported LDL, does not know your full clinical picture, and cannot substitute for a healthcare professional's interpretation of your results.

Use your lab's directly-reported LDL whenever it's available — especially if your triglycerides are elevated, since that is exactly the scenario where the calculated value is least trustworthy. Bring your full lipid panel, not just the LDL number, to any conversation with your clinician about cardiovascular risk and treatment.

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Questions

Frequently Asked Questions

6 questions

What is the Friedewald formula?+

LDL = Total cholesterol − HDL − (Triglycerides / 5), all in mg/dL. It estimates LDL cholesterol from a standard lipid panel without a direct LDL measurement.

Why divide triglycerides by 5?+

Dividing triglycerides by 5 approximates VLDL cholesterol, since VLDL particles typically carry about one-fifth as much cholesterol as triglyceride by mass. Subtracting that estimated VLDL, along with HDL, from total cholesterol leaves LDL.

When is the Friedewald formula invalid?+

When triglycerides are 400 mg/dL (about 4.5 mmol/L) or higher. Above that level the TG/5 approximation of VLDL breaks down, and a directly measured (not calculated) LDL is needed.

What is the mmol/L version of the formula?+