On most lipid panels, LDL cholesterol is not measured directly — it's calculated. The Friedewald formula has been the workhorse since 1972 and still is. It has one well-known weak spot: high triglycerides.
This guide walks through the formula in both unit systems, classifies the result against ATP III, and shows when a direct LDL assay is the better call.
The formula — two flavours
Background: Triglycerides / 5 (or / 2.2 in mmol/L) estimates the VLDL cholesterol fraction. Subtract HDL and VLDL from total cholesterol and what remains is the LDL estimate.
Example: Total 200, HDL 50, triglycerides 150 → LDL = 200 − 50 − 30 = 120 mg/dL. That sits in the "near optimal" range.
ATP III bands at a glance
LDL classification (NCEP ATP III)
ATP III cut-offs come from the US guideline and are defined in mg/dL. European ESC guidelines sometimes use different LDL targets based on cardiovascular risk strata.
When Friedewald breaks down
Main limit
Triglycerides ≥ 400 mg/dL (4.5 mmol/L) → Friedewald underestimates LDL. Request a direct measurement.
Why? The "VLDL = TG/5" assumption only holds at moderate triglyceride levels. With hypertriglyceridemia — after a heavy meal, in diabetes, or with pancreatitis risk — chylomicron-like particles skew the ratio.
Newer estimators like Sampson (2020) and Martin-Hopkins (2013) correct this weakness and perform better at very low LDL or high triglycerides.
What matters before the test
- →Fast fully for 9–12 hours (water is fine)
- →No alcohol in the 24 hours before the draw
- →No acute illness or surgery in the past 2–6 weeks
- →Rested and calm (stress shifts the lipid profile)
Estimate your LDL now
Enter total cholesterol, HDL and triglycerides — the calculator returns the Friedewald LDL and the ATP III band.
Open the LDL Friedewald CalculatorWhat lowers high LDL
LDL responds well to diet, exercise and weight. Three levers with the strongest evidence:
- 1.Cut saturated and trans fats: Less fatty meat, sausage, butter, and fried food.
- 2.More soluble fibre: Oats, legumes, apples, flaxseed bind cholesterol in the gut.
- 3.Regular exercise plus weight loss: Lowers LDL and triglycerides, raises HDL.
For LDL ≥ 190 mg/dL — or added cardiovascular risk factors — clinicians often recommend a statin. Lifestyle remains the foundation either way.
Related topics
LDL is one piece of the picture. For broader context try the Cholesterol Ratio Calculator (Total/HDL), the Cardiovascular Risk Calculator (Framingham/SCORE2), and the Stroke Risk Calculator for atrial fibrillation.
Takeaway
The Friedewald formula gives a reliable LDL for the vast majority of routine cases — from three values every lab measures anyway.
It breaks once triglycerides climb past 400 mg/dL. That's when a direct measurement is the next step. Whatever the method, lifestyle moves LDL fastest and farthest.
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