GFR Calculator

GFR Calculator

GFR / eGFR Calculator

GFR Calculator

The Glomerular Filtration Rate (GFR) Calculator helps estimate kidney function by calculating GFR values using factors such as serum creatinine, age, gender, and race. To improve accuracy, it provides results using three widely accepted formulas.

What is GFR?

Glomerular Filtration Rate (GFR) is a measure of how quickly blood is filtered through the tiny filters in the kidneys (glomeruli). It is one of the most important indicators of kidney health

  • A higher GFR usually reflects better kidney performance.
  • A lower GFR suggests reduced kidney function, meaning the kidneys are filtering less fluid per minute.

For healthy adults under 40, normal GFR ranges are typically:

  • Men: 100–130 mL/min/1.73m²
  • Women: 90–120 mL/min/1.73m²

After the age of 40, GFR naturally declines with age.

Average GFR by Age

Age Group Mean Estimated GFR (mL/min/1.73m²)
20–29 116
30–39 107
40–49 99
50–59 93
60–69 85
70+ 75

GFR and Kidney Disease Stages

A GFR above 60 mL/min/1.73m² is usually considered sufficient for most people. However, if values show a significant decline compared to earlier tests, it may point toward the early development of kidney disease. Detecting kidney problems early gives patients a better chance to slow progression and avoid dialysis.
Stage GFR Range (mL/min/1.73m²) Description
Normal 90+ with no proteinuria Healthy kidney function
CKD 1 90+ with signs of kidney damage Early kidney disease
CKD 2 60–89 with kidney damage Mild stage
CKD 3 30–59 Moderate stage
CKD 4 15–29 Severe stage
CKD 5 < 15 Kidney failure

How GFR is Measured

The gold standard test for measuring GFR is inulin clearance. Inulin passes through the kidneys without being reabsorbed or secreted, making it an accurate marker. However, this method requires:
  • Continuous intravenous infusion
  • Multiple timed blood and urine collections
  • Specialized equipment
Because of these challenges, inulin clearance is not used in routine practice. Instead, GFR is usually estimated using creatinine-based formulas.

Limitations of Creatinine-Based GFR Estimates

Creatinine is a waste product of muscle metabolism. Since muscle mass varies by person, the same creatinine level may reflect different kidney functions. For example:
  • People with higher muscle mass may naturally have higher creatinine.
  • Creatinine clearance often overestimates GFR by 10–20% due to small amounts being actively secreted by the body.
Still, creatinine-based methods remain practical and widely used.

Common Formulas for Estimating GFR

1. MDRD (IDMS-Traceable) Formula

GFR = 175 × (SCr)−1.154 × (Age)−0.203 × (0.742 if female) × (1.212 if Black)

where SCr = serum creatinine (mg/dL)

2. CKD-EPI Equation
Black Female
  • If SCr < 0.7 → GFR = 166 × (SCr/0.7)−0.329 × (0.993)Age
  • If SCr ≥ 0.7 → GFR = 166 × (SCr/0.7)−1.209 × (0.993)Age
Black Male
  • If SCr < 0.9 → GFR = 163 × (SCr/0.9)−0.411 × (0.993)Age
  • If SCr ≥ 0.9 → GFR = 163 × (SCr/0.9)−1.209 × (0.993)Age
Non-Black Female
  • If SCr < 0.7 → GFR = 144 × (SCr/0.7)−0.329 × (0.993)Age
  • If SCr ≥ 0.7 → GFR = 144 × (SCr/0.7)−1.209 × (0.993)Age
Non-Black Male
  • If SCr < 0.9 → GFR = 141 × (SCr/0.9)−0.411 × (0.993)Age
  • If SCr ≥ 0.9 → GFR = 141 × (SCr/0.9)−1.209 × (0.993)Age
3. Mayo Quadratic Formula
If SCr < 0.8 mg/dL, use 0.8 instead.

GFR = e(1.911 + 5.249/SCr − 2.114/SCr² − 0.00686 × Age − (0.205 if female))

4. Schwartz Formula (for Children)

GFR = 0.413 × Height (cm) SCr

In summary, GFR is a crucial marker for kidney health. While direct measurement methods like inulin clearance are highly accurate, creatinine-based formulas such as MDRD, CKD-EPI, and Mayo are more practical for everyday clinical use.