Cholesterol Ratio Calculator (TC/HDL + LDL)
Calculate your total cholesterol/HDL ratio and estimate LDL with the Friedewald equation. See risk categories against AHA and CDC reference ranges.
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Full bio →TC/HDL Ratio = Total Cholesterol ÷ HDL. LDL is estimated with the Friedewald equation: LDL = Total Cholesterol − HDL − (Triglycerides ÷ 5) in mg/dL, or − (Triglycerides ÷ 2.2) in mmol/L. This estimate becomes unreliable at triglycerides of 400 mg/dL (≈4.52 mmol/L) or higher, so this calculator blocks the LDL result above that threshold rather than showing a misleading number. HDL risk thresholds shown here use the general (men's) below-40 mg/dL cutoff — the risk threshold for women is below 50 mg/dL. This tool is an educational estimate, not a diagnosis — always review your full lipid panel with a doctor.
Reference Values
Last verified:| Category | Range | What It Means | Status |
|---|---|---|---|
| Total Cholesterol ★ | Desirable: below 200 mg/dL | Borderline high is 200–239 mg/dL; 240 mg/dL and above is high. Total cholesterol includes LDL, HDL, and a portion of triglycerides — it's a starting screen, not the full picture. | ★ Best |
| LDL ("bad" cholesterol) ★ | Optimal: below 100 mg/dL | 100–129 near optimal, 130–159 borderline high, 160–189 high, 190+ very high. Very-high-risk patients (existing heart disease) are often given a stricter goal of below 70 mg/dL by their doctor. | ★ Best |
| HDL ("good" cholesterol) ★ | Protective: 60 mg/dL and above | Below 40 mg/dL is a risk factor for men; the risk threshold is below 50 mg/dL for women. Higher HDL helps clear cholesterol from the bloodstream, which is why it's scored in the opposite direction from LDL. | ★ Best |
| Triglycerides ★ | Normal: below 150 mg/dL | 150–199 borderline high, 200–499 high, 500+ very high. At 500 mg/dL and above, triglycerides also raise acute pancreatitis risk, not just heart disease risk. | ★ Best |
| TC/HDL Ratio ★ | Optimal: below 3.5 | Below 5.0 is generally considered the desirable upper limit; 5.0 and above indicates increased cardiovascular risk. This ratio is a quick risk-screening number, not a diagnosis on its own. | ★ Best |
| Friedewald LDL limitation | Invalid when triglycerides ≥ 400 mg/dL | The Friedewald equation assumes a fixed ratio between triglycerides and VLDL cholesterol that breaks down at high triglyceride levels, producing an unreliable or falsely low LDL estimate. A direct LDL blood test (or the Martin-Hopkins method) is needed above this threshold. | Poor |
Source: American Heart Association, "What Your Cholesterol Levels Mean"; CDC, "About Cholesterol"; Friedewald WT et al. (1972) Clinical Chemistry — original LDL estimation formula; MDCalc, "LDL Calculated" (Friedewald Equation) methodology notes.
Worked Examples
Optimal Lipid Panel
- Total Cholesterol
- 170 mg/dL
- HDL
- 65 mg/dL
- Triglycerides
- 90 mg/dL
Ratio = 170 ÷ 65 = 2.62 (optimal, below 3.5). LDL = 170 − 65 − (90 ÷ 5) = 170 − 65 − 18 = 87 mg/dL (optimal, below 100). Every marker here falls in the desirable range.
Borderline Panel
- Total Cholesterol
- 210 mg/dL
- HDL
- 45 mg/dL
- Triglycerides
- 150 mg/dL
Ratio = 210 ÷ 45 = 4.67 (still under the 5.0 desirable ceiling, but well above the 3.5 optimal mark). LDL = 210 − 45 − (150 ÷ 5) = 210 − 45 − 30 = 135 mg/dL, which lands in the borderline-high LDL band (130–159).
High-Risk Panel
- Total Cholesterol
- 260 mg/dL
- HDL
- 35 mg/dL
- Triglycerides
- 180 mg/dL
Ratio = 260 ÷ 35 = 7.43 (above the 5.0 increased-risk threshold). LDL = 260 − 35 − (180 ÷ 5) = 260 − 35 − 36 = 189 mg/dL, just under the "high" LDL cutoff of 190. HDL of 35 mg/dL is also below the 40 mg/dL risk-factor threshold for men.
Triglycerides Too High for Friedewald (Invalid LDL)
- Total Cholesterol
- 220 mg/dL
- HDL
- 40 mg/dL
- Triglycerides
- 450 mg/dL
Ratio = 220 ÷ 40 = 5.50 (increased risk). But triglycerides of 450 mg/dL exceed the 400 mg/dL ceiling for the Friedewald equation, so the LDL estimate would be unreliable — this calculator blocks the LDL result and flags that a direct LDL blood test is needed instead.
Same Panel in mmol/L (International Units)
- Total Cholesterol
- 5.2 mmol/L
- HDL
- 1.3 mmol/L
- Triglycerides
- 1.7 mmol/L
Ratio = 5.2 ÷ 1.3 = 4.00 (same math regardless of unit, since TC and HDL are in the same unit). Converted to mg/dL for the Friedewald step (TC ≈ 201.1, HDL ≈ 50.3, TG ≈ 150.6), LDL ≈ 120.7 mg/dL, converted back to ≈ 3.13 mmol/L.
How to Use This Calculator
- 1
Choose your units
Select mg/dL (standard in the US) or mmol/L (standard internationally) — use whichever unit your lab report shows.
- 2
Enter your lipid panel values
Total cholesterol, HDL, and triglycerides, all from the same fasting or non-fasting blood draw as reported on your lab results.
- 3
Read your TC/HDL ratio and estimated LDL
The ratio and Friedewald-estimated LDL calculate instantly, each shown with its AHA/CDC risk category.
- 4
Check the triglycerides warning if it appears
If triglycerides are 400 mg/dL (or ≈4.52 mmol/L) or higher, the LDL estimate is blocked because the Friedewald formula becomes unreliable at that level — a direct LDL test is needed instead.
What Each Value Means
- TC/HDL Ratio (ratio (unitless))
- Total cholesterol divided by HDL cholesterol. A quick screening number for cardiovascular risk — lower is better, since it means relatively more of your cholesterol is the protective HDL type.
- LDL (Friedewald estimate) (mg/dL or mmol/L)
- "Bad" cholesterol, estimated using the Friedewald equation from total cholesterol, HDL, and triglycerides rather than measured directly. Higher LDL is associated with greater plaque buildup risk in the arteries.
- Triglycerides (mg/dL or mmol/L)
- A type of blood fat used in the Friedewald equation to estimate VLDL cholesterol. High triglycerides both raise cardiovascular risk directly and, above 400 mg/dL, invalidate the Friedewald LDL estimate.