📊 eGFR Calculator – Estimate Your Kidney Filtration Rate
The estimated Glomerular Filtration Rate (eGFR) is the most widely used clinical marker of kidney function. It represents the volume of blood the kidneys filter every minute, normalized to a standard body surface area of 1.73 m². This calculator supports four validated equations — CKD-EPI 2021 Creatinine, CKD-EPI Cystatin C, CKD-EPI Combined, and the Bedside Schwartz pediatric equation — so you can choose the formula that best fits your available lab values.
🔬 Why eGFR Matters
Chronic kidney disease (CKD) affects an estimated 10–15 % of the global adult population, and many people remain undiagnosed until the disease is advanced. eGFR is derived from routine blood tests — primarily serum creatinine — making it a cost-effective screening tool. A single low eGFR reading does not diagnose CKD; guidelines require persistent impairment on at least two measurements separated by three months, often accompanied by other markers such as albuminuria, imaging findings, or biopsy results.
📐 Supported Equations
CKD-EPI 2021 Creatinine
The 2021 race-free CKD-EPI Creatinine equation is the current standard for adults. It removed race as a variable compared with the 2009 version to eliminate systematic underdiagnosis in Black patients. The formula uses serum creatinine, age, and biological sex:
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^Age × 1.012 [if female]
Female: κ = 0.7, α = −0.241
Male: κ = 0.9, α = −0.302CKD-EPI Cystatin C
Cystatin C is a small protein produced at a near-constant rate by all nucleated cells. Unlike creatinine, it is not significantly affected by muscle mass, protein intake, or physical activity. This equation is preferred when creatinine-based estimates may be unreliable — for example in patients with extreme muscle mass, sarcopenia, vegetarian diets, or on certain medications such as trimethoprim.
CKD-EPI 2021 Combined
When both serum creatinine and cystatin C are available, the combined equation yields the most accurate eGFR estimate. It reduces individual biomarker variability and is increasingly recommended in clinical practice for confirmatory testing and drug-dosing decisions.
Bedside Schwartz (Pediatric)
Designed for children under 18, this simplified formula requires only height and serum creatinine:
eGFR = 0.413 × Height (cm) / Scr (mg/dL)The 0.413 constant was derived from a large multicenter pediatric cohort and is appropriate for children regardless of sex.
🏷️ CKD Staging by eGFR
The Kidney Disease: Improving Global Outcomes (KDIGO) guideline classifies kidney function into six eGFR-based stages:
| Stage | eGFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure |
It is important to note that eGFR staging is not the only factor in CKD classification. KDIGO also considers albuminuria categories (A1–A3) based on urine albumin-to-creatinine ratio, which further refines prognosis even within the same eGFR stage.
⚖️ Normalized vs. Absolute GFR
Standard eGFR is indexed to a reference BSA of 1.73 m², allowing comparison across individuals of different body sizes. For patients with a BSA substantially different from 1.73 m² — such as very small adults or obese individuals — converting to absolute GFR may be more clinically meaningful, particularly for drug dosing.
BSA (Du Bois) = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425
Absolute GFR = eGFR × (BSA / 1.73)Enter both height and weight in this calculator to enable the optional absolute GFR output.
⚠️ Factors That Affect eGFR Accuracy
Creatinine-based limitations
- High muscle mass (overestimates GFR)
- Sarcopenia or low muscle mass (underestimates GFR)
- High dietary meat intake raises creatinine
- Vegetarian/vegan diet lowers creatinine
- Trimethoprim, cimetidine block tubular creatinine secretion
- Acute kidney injury — values may change rapidly
Cystatin C limitations
- Elevated in thyroid dysfunction
- Corticosteroids raise cystatin C independently of GFR
- Less widely available than creatinine
- Higher cost per lab test
- Not validated below 1 year of age
🩺 Clinical Interpretation Tips
A single isolated eGFR measurement should never be interpreted in isolation. Always consider:
- Trend over time — a declining eGFR is more clinically significant than a single borderline value.
- Clinical context — recent illness, dehydration, contrast agent exposure, or surgery can cause transient eGFR drops.
- Albuminuria — even a normal eGFR with significant proteinuria warrants nephrology evaluation.
- Medications— many drugs require dose adjustment when eGFR falls below defined thresholds (e.g., metformin < 30, direct anticoagulants at various thresholds).
This tool is intended for educational and informational purposes only. It does not replace clinical judgment, laboratory standards, or the advice of a qualified healthcare professional. Always discuss your results with your care team.