GFR (Glomerular Filtration Rate) Calculator
Use this professional-grade calculator to estimate kidney function with the CKD-EPI 2021 creatinine equation (race-free). Designed for clinicians, researchers, and informed patients, it converts units, optionally adjusts for body size, and explains CKD staging. This tool does not replace clinical judgment.
Interactive Calculator
Results
Data Source and Methodology
Authoritative source: National Kidney Foundation (NKF) — Professional eGFR Calculators . Primary equation reference: Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. JAMA. 2021;326(19):2043–2054. doi:10.1001/jama.2021.17376
All calculations are strictly based on the formulas and data provided by this source.
The Formula Explained
For adults, CKD-EPI 2021 (creatinine, no race):
$$\mathrm{eGFR} = 142 \times \min\!\left(\frac{S_{cr}}{k},\,1\right)^{\alpha} \times \max\!\left(\frac{S_{cr}}{k},\,1\right)^{-1.200} \times 0.9938^{\text{Age}} \times 1.012^{[\text{female}]}\,,$$
where $$k = \begin{cases} 0.7 & \text{if female} \\ 0.9 & \text{if male} \end{cases} \qquad \alpha = \begin{cases} -0.241 & \text{if female} \\ -0.302 & \text{if male} \end{cases} $$
Unit conversion (if needed): $$S_{cr}(\mathrm{mg/dL})=\frac{S_{cr}(\mu\mathrm{mol}/\mathrm{L})}{88.4}$$
Optional body size adjustment (Du Bois): $$\mathrm{BSA}=0.007184\times \mathrm{Height}^{0.725}\times \mathrm{Weight}^{0.425}$$ with Height in cm and Weight in kg, and $$\mathrm{Absolute\ GFR}=\mathrm{eGFR}\times \frac{\mathrm{BSA}}{1.73}.$$
Glossary of Variables
| Name | Symbol/Unit | Definition |
|---|---|---|
| Age | years | Patient age in completed years (adults ≥18). |
| Sex | — | Biological sex (female/male) used by the CKD-EPI coefficients. |
| Serum Creatinine | Scr (mg/dL or µmol/L) | Creatinine concentration measured by the laboratory. |
| eGFR | mL/min/1.73 m² | Estimated GFR normalized to body surface area using CKD-EPI 2021. |
| Height | cm or in | Body height, used to estimate BSA (optional). |
| Weight | kg or lb | Body weight, used to estimate BSA (optional). |
| BSA | m² | Estimated body surface area (Du Bois formula). |
| Absolute GFR | mL/min | eGFR adjusted to individualized BSA: eGFR × (BSA/1.73). |
| CKD Stage | G1–G5 | Stage classification based on eGFR; albuminuria and clinical context are also required. |
Worked Example
How It Works: A Step-by-Step Example
Inputs: Age = 55 years, Sex = Female, Serum Creatinine = 1.10 mg/dL. Optional body size: Height = 165 cm, Weight = 65 kg.
- Coefficients: k = 0.7 (female), α = −0.241.
- Compute ratios: Scr/k = 1.10 / 0.7 ≈ 1.571. Then min(Scr/k,1) = 1; max(Scr/k,1) ≈ 1.571.
- Apply exponents: 1^α = 1; 1.571^(−1.200) ≈ 0.582.
- Age term: 0.9938^55 ≈ 0.711. Female factor: × 1.012.
- eGFR: 142 × 1 × 0.582 × 0.711 × 1.012 ≈ 59.5 mL/min/1.73 m².
- BSA (Du Bois): 0.007184 × 165^0.725 × 65^0.425 ≈ 1.715 m².
- Absolute GFR: 59.5 × (1.715 / 1.73) ≈ 58.9 mL/min.
Resulting CKD stage would be G3a based on eGFR alone; albuminuria and clinical evaluation are required for full staging.
Frequently Asked Questions (FAQ)
Which equation does this calculator use?
It implements the CKD-EPI 2021 creatinine equation without race, aligned with recommendations from NKF and ASN.
Can I enter creatinine in µmol/L?
Yes. Select µmol/L from the units dropdown. The tool converts to mg/dL internally using 1 mg/dL = 88.4 µmol/L.
Who should not rely on this calculator?
Not validated for children, pregnancy, acute kidney injury, or situations with rapidly changing renal function or extreme muscle mass/diet.
What is the difference between eGFR and absolute GFR?
eGFR is normalized to a standard BSA of 1.73 m². Absolute GFR scales eGFR to your estimated BSA from height and weight.
How is CKD staged?
By eGFR bands (G1≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5<15) and albuminuria categories (A1–A3); clinical correlation is essential.
Does muscle mass affect creatinine and eGFR?
Yes. Low muscle mass can lower creatinine leading to higher eGFR estimates; the inverse is also true. Consider cystatin C when appropriate.
Is this tool a substitute for medical advice?
No. It provides educational estimates only. Decisions must be made by qualified clinicians using the full clinical picture.