---
title: LDL Cholesterol Calculator (Friedewald & NIH Equations)
type: tool
url: "https://www.test-well.com/tools/ldl-cholesterol-calculator"
date_published: 2026-10-12
free: true
---

# LDL Cholesterol Calculator (Friedewald & NIH Equations)

> Enter total cholesterol, HDL and fasting triglycerides and the calculator estimates LDL cholesterol with the Friedewald equation when triglycerides are under 400 mg/dL and the newer Sampson/NIH equation when they are higher, and shows non-HDL cholesterol and the total-to-HDL ratio alongside. The LDL is read against the NCEP categories — optimal under 100, borderline high 130–159, high 160 and above.

## Key facts

| Fact | Value |
| --- | --- |
| Inputs | Total · HDL · triglycerides |
| Equations | Friedewald · Sampson/NIH |
| Also shown | Non-HDL · TC:HDL |
| Cost | Free |

## For agents

See https://www.test-well.com/developers for the agent endpoints.

## Frequently asked questions

### Why is LDL calculated instead of measured?

Most routine lipid panels estimate LDL from the other three values because the direct assay costs more and the estimate is accurate for most people. The Friedewald equation subtracts HDL and a fifth of the triglycerides from total cholesterol; it loses accuracy as triglycerides rise, which is why laboratories switch to a direct LDL or a newer equation at 400 mg/dL.

### What is the difference between Friedewald and the Sampson/NIH equation?

Friedewald (1972) assumes triglyceride-rich particles carry a fixed fifth of their weight as cholesterol, which fails at high triglycerides and at low LDL. The Sampson/NIH equation (2020) was fitted to ultracentrifugation data and stays accurate up to triglycerides of about 800 mg/dL and at LDL values below 70, where modern treatment targets sit.

### What is non-HDL cholesterol and why does it matter?

Non-HDL is total cholesterol minus HDL — the cholesterol in every plaque-forming particle, including the triglyceride-rich ones the LDL number misses. It needs no fasting and is a secondary target in the 2018 AHA/ACC guideline, usually set about 30 mg/dL above the LDL goal.

### Do I need to fast for the inputs?

For an accurate estimate, yes: triglycerides rise for hours after a meal and inflate the correction term, lowering the calculated LDL. Guidelines accept non-fasting panels for screening, but a value near a treatment threshold should come from a 9–12 hour fast or a direct LDL measurement.

## Related

- [ldl cholesterol](https://www.test-well.com/biomarkers/ldl-cholesterol)
- [hdl cholesterol](https://www.test-well.com/biomarkers/hdl-cholesterol)
- [total cholesterol](https://www.test-well.com/biomarkers/total-cholesterol)
- [triglycerides](https://www.test-well.com/biomarkers/triglycerides)
- [non hdl cholesterol](https://www.test-well.com/biomarkers/non-hdl-cholesterol)
- [apolipoprotein b](https://www.test-well.com/biomarkers/apolipoprotein-b)
- [lipid panel](https://www.test-well.com/tests/lipid-panel)
- [apolipoprotein b](https://www.test-well.com/tests/apolipoprotein-b)
- [advanced lipid panel](https://www.test-well.com/tests/advanced-lipid-panel)
- [heart health panel](https://www.test-well.com/tests/heart-health-panel)

---

Canonical page: https://www.test-well.com/tools/ldl-cholesterol-calculator
Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt

Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.