eGFR Calculator (CKD-EPI 2021)

How the eGFR Calculator Works

This calculator estimates your glomerular filtration rate (eGFR) — how well your kidneys clear waste — using the 2021 CKD-EPI creatinine equation, the current race-free standard recommended by the National Kidney Foundation and the American Society of Nephrology. Enter your serum creatinine, age, and sex, and it returns your eGFR in mL/min/1.73 m² along with the corresponding chronic kidney disease (CKD) stage.

The Formula

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^Age × 1.012 [if female]

where serum creatinine (Scr) is in mg/dL and the sex-specific constants are:

Parameter	Female	Male
κ (kappa)	0.7	0.9
α (alpha)	−0.241	−0.302

The 1.012 multiplier applies only to women. If your lab reports creatinine in µmol/L, divide by 88.4 to get mg/dL first.

Worked Example

For a 60-year-old male with serum creatinine 1.0 mg/dL:

• κ = 0.9, so Scr/κ = 1.0 / 0.9 = 1.111
• Since the ratio is above 1, the min term = 1 and the max term = 1.111^−1.200 = 0.881
• Age factor = 0.9938^60 = 0.689
• eGFR = 142 × 1 × 0.881 × 0.689 = ≈ 86 mL/min/1.73 m² (stage G2, mild reduction)

Understanding the Result

A single eGFR is a snapshot. Kidney function naturally declines with age, and creatinine can be affected by muscle mass, recent meat intake, hydration, and some medications. Chronic kidney disease is diagnosed when eGFR stays below 60 mL/min/1.73 m² for at least three months, or when there are other markers of kidney damage such as albumin in the urine.

Important Limitations

This tool is for adults aged 18 and over; children require pediatric equations such as the bedside CKiD formula. eGFR estimates are less reliable at very high values, in people with unusual body composition (very high or low muscle mass), during acute illness, in pregnancy, and at the extremes of creatinine. Always interpret your eGFR with a clinician, who can combine it with urine tests, your history, and trends over time. This calculator does not provide medical advice.