# GFR Calculator

> Estimate glomerular filtration rate from serum creatinine, age and sex with the race-free CKD-EPI 2021 equation, with the KDIGO GFR category.

Category: Health & fitness · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/gfr-calculator

Estimated GFR (eGFR) gauges kidney filtration from a blood creatinine result using the CKD-EPI 2021 equation. It supports, and does not replace, clinical judgement.

Also called: eGFR calculator, CKD-EPI calculator.

## Inputs
- Serum creatinine (default 1.0)
- Creatinine unit (options: mg/dL, µmol/L; default mgdl)
- Age (unit years; default 50)
- Sex (options: Male, Female; default male)

## Results
- eGFR
- KDIGO GFR category
- Creatinine used

## Formula

```
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^Age × 1.012 [if female];  κ = 0.7 (F) or 0.9 (M);  α = −0.241 (F) or −0.302 (M)
```

Where:
- Scr: serum creatinine in mg/dL (µmol/L ÷ 88.4)
- Age: age in years (adults only)
- κ, α: sex-specific constants

## Worked example
1. Scr/κ = 1.0 ÷ 0.9 = 1.111, so the min term is 1 and the max term is 1.111^−1.200 = 0.881.
2. Age term: 0.9938^50 = 0.733.
3. eGFR = 142 × 0.881 × 0.733 ≈ 91.7, reported as 92 mL/min/1.73 m².

**Result:** A 50-year-old man with a creatinine of 1.0 mg/dL has an eGFR of about 92 mL/min/1.73 m², KDIGO category G1.

## What the result means

KDIGO categories: G1 ≥ 90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 < 15 mL/min/1.73 m². Chronic kidney disease is diagnosed only when a reduced GFR or kidney damage (such as albumin in the urine) persists for more than three months, so one result on its own is not a diagnosis.

## Assumptions and limits
- Adult (18 or over) with stable kidney function.
- Creatinine measured with an IDMS-traceable method.
- Result is indexed to a standard body surface area of 1.73 m².
- Unreliable in acute kidney injury, pregnancy, very high or very low muscle mass (amputation, bodybuilding, frailty), high-protein diets or creatine supplements, and some medicines that change creatinine.
- For drug dosing, the product label may specify Cockcroft–Gault creatinine clearance or a non-indexed GFR.
- Cystatin C–based equations may be preferred when creatinine is misleading.

## Questions

### Why does the 2021 equation not use race?

The CKD-EPI 2021 refit removed the race coefficient used in the 2009 equation, so eGFR now depends only on creatinine, age and sex.

### Is my eGFR low because of age?

eGFR falls gradually with age in most people. Whether a value matters depends on trends over time, urine albumin and other findings, which a clinician interprets.

## Sources
- [National Kidney Foundation: CKD-EPI Creatinine Equation (2021)](https://www.kidney.org/professionals/ckd-epi-creatinine-equation-2021)

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_This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/gfr-calculator