eGFR & Creatinine Clearance Calculator (CKD-EPI 2021)

eGFR and Creatinine Clearance Calculator

Estimated glomerular filtration rate (eGFR) is a number that describes how fast the kidneys filter blood. This calculator estimates it from sex, age and serum creatinine using the CKD-EPI 2021 equation, and it also estimates creatinine clearance from the Cockcroft-Gault equation when a body weight is entered.

Creatinine is a waste product made by muscle. Healthy kidneys remove it, so the amount left in the blood rises when filtration slows. Both equations turn that blood level into an estimate of filtration.

What the calculator shows

The inputs produce four outputs.

Age is accepted from 18 to 120 years. Serum creatinine can be entered in mg/dL or in µmol/L. Body weight can be entered in kilograms or pounds and is optional, because only Cockcroft-Gault uses it.

The CKD-EPI 2021 formula

The calculator uses the race-free 2021 creatinine equation from the Chronic Kidney Disease Epidemiology Collaboration:

$G = 142 \times \min\left(\tfrac{S}{\kappa},\, 1\right)^{\alpha} \times \max\left(\tfrac{S}{\kappa},\, 1\right)^{−1.200} \times 0.9938^{A} \times 1.012$

where:

• S is serum creatinine in mg/dL.
• κ (kappa) is 0.7 for females and 0.9 for males.
• α (alpha) is −0.241 for females and −0.302 for males.
• A is age in years.
• The last factor applies to females only and is dropped for males.
• G is the result, in mL/min per 1.73 m² of body surface area.

The two power terms split the equation at $\kappa$. When creatinine is at or below $\kappa$, the $\alpha$ exponent applies and the second term is 1. When creatinine is above $\kappa$, the first term is 1 and the $−1.200$ exponent applies. The factor $0.9938^{A}$ lowers the estimate by about 0.62% for each year of age.

Source: Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR Without Race. New England Journal of Medicine. 2021;385(19):1737-1749.

The older 2009 CKD-EPI equation multiplied the result by an extra coefficient for Black patients. The NKF-ASN Task Force recommended removing that coefficient and moving to the 2021 equation, so this calculator asks no question about race (Delgado C, Baweja M, Crews DC, et al. A Unifying Approach for GFR Estimation. American Journal of Kidney Diseases. 2022;79(2):268–288).

The Cockcroft-Gault formula

Creatinine clearance is the volume of blood plasma cleared of creatinine each minute. The calculator estimates it with the 1976 Cockcroft-Gault equation:

$C = \frac{(140 − A) \times W}{72 \times S} \times 0.85$

where C is creatinine clearance in mL/min, A is age in years, W is body weight in kilograms, S is serum creatinine in mg/dL, and the last factor applies to females only.

Source: Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41.

The weight used is actual body weight, the total weight of the person, because that is the weight the 1976 paper used. Ideal body weight and adjusted body weight are later conventions and give a lower number in heavier people, so the choice changes the answer.

This result is in plain mL/min. It is not scaled to a standard body size, so it is not directly comparable with the eGFR figure above it.

KDIGO GFR categories

The calculator labels the eGFR with the GFR category defined in the KDIGO 2024 chronic kidney disease guideline (Kidney International. 2024;105(4S):S117-S314):

The band is read from the unrounded eGFR, while the figure on screen is rounded to a whole number the way laboratories report it. The two can look inconsistent. A female aged 50 with a creatinine of 0.80 mg/dL has an eGFR of 89.707, which displays as 90 and still sits in G2. The calculator prints a short note whenever rounding crosses a boundary like that.

A category says which band one value falls in. The same guideline defines chronic kidney disease as abnormalities of kidney structure or function that have lasted more than three months, so a band on its own is not a diagnosis.

Worked example

A female aged 55 with a serum creatinine of 0.90 mg/dL and a body weight of 70 kg.

CKD-EPI 2021. $\kappa$ is 0.7, so $S/\kappa$ = 0.90 / 0.7 = 9/7, or about 1.286, which is above 1. The $\min$ term is therefore 1 and only the $−1.200$ exponent applies:

• (9/7)^−1.200 = 0.7396506
• 0.9938^55 = 0.7103045
• 142 × 0.7396506 × 0.7103045 × 1.012 = 75.4988

The ratio is kept as the fraction 9/7 rather than a rounded 1.286, because rounding it first changes the fourth decimal of the answer.

The eGFR displays as 75 mL/min/1.73 m², which falls in category G2.

Cockcroft-Gault, using the same creatinine and the 70 kg weight:

• (140 − 55) × 70 = 5,950
• 72 × 0.90 = 64.8
• 5,950 / 64.8 = 91.821
• 91.821 × 0.85 (female) = 78.0478

The clearance displays as 78.0 mL/min. The creatinine echo shows 0.90 × 88.4 = 79.56 µmol/L.

A second example, a male aged 60 with a creatinine of 1.00 mg/dL and a weight of 80 kg: $S/\kappa$ = 1.00 / 0.9 = 10/9, (10/9)^−1.200 = 0.8812335, and 0.9938^60 = 0.6885564, so the eGFR is 142 × 0.8812335 × 0.6885564 = 86.163, shown as 86 and in category G2. Cockcroft-Gault gives (140 − 60) × 80 / (72 × 1.00) = 6,400 / 72 = 88.889, shown as 88.9 mL/min, with no 0.85 factor.

Unit conversions

Both equations take creatinine in mg/dL, so a µmol/L entry is converted first:

$S = \frac{U}{88.4}$

where U is serum creatinine in µmol/L and S the same value in mg/dL.

Creatinine has the formula C₄H₇N₃O and a molar mass of 113.12 g/mol. One mg/dL is 10 mg/L, and 10 ÷ 113.12 gives 0.0884017 mmol/L, which is 88.4017 µmol/L. Standard SI conversion tables publish that as 88.4, and 88.4 is the figure the calculator uses.

Pounds convert with the exact international avoirdupois definition, 1 lb = 0.45359237 kg (NIST Special Publication 811).

Limitations

• Both equations assume serum creatinine is steady. Creatinine lags behind a changing filtration rate, so neither number describes kidney function during acute kidney injury or any other period when it is moving quickly.
• Creatinine comes from muscle, so a creatinine-based estimate is unreliable at the extremes of body size and muscle mass. High muscle mass, creatine supplements and large amounts of cooked meat push the estimate down. Amputation, low muscle mass, malnutrition and advanced liver disease push it up.
• CKD-EPI 2021 was developed and validated in adults. The calculator returns nothing for an age under 18 rather than extrapolating a children's estimate.
• The Cockcroft-Gault equation came from a study of 249 men. No women were in that group, so the 0.85 factor was the authors' estimate. Creatinine assays have also changed since 1976 and now read a little lower, so the equation tends to give a number above the older results it was fitted to.
• Creatinine clearance runs roughly 10% to 20% higher than the true filtration rate, because the kidney secretes some creatinine into the urine on top of what it filters. Clearance and filtration are different quantities.
• Neither equation is validated in pregnancy or in children.

Frequently asked questions

What is the difference between eGFR and creatinine clearance? eGFR estimates the filtration rate scaled to a standard body surface area of 1.73 m², so two people of different sizes can be compared on one scale. Creatinine clearance is not scaled and describes the person's own body, so it changes with weight. The two numbers use different equations and different units and will not match.

Why does the calculator not ask about race? The 2021 CKD-EPI equation has no race coefficient. The 2009 version did, and the NKF-ASN Task Force recommended dropping it and adopting the race-free equation, which is the one implemented here.

Can creatinine be entered in µmol/L? Yes. Most laboratories outside the United States report µmol/L. The calculator divides by 88.4 to get mg/dL, and it also shows the entered value in the other unit so it can be checked against a lab report.

Why is body weight optional? CKD-EPI 2021 does not use weight, so an eGFR and its category appear without one. Cockcroft-Gault does use weight, so that field stays empty until a weight is entered.

Why does the tool refuse an age under 18? Both equations were derived in adults. Using them on a child would apply a curve fitted to adult data outside the range it was built on, so the calculator returns no result instead.

What does a body surface area of 1.73 m² mean? It is a reference body size used to standardise the number, close to the average surface area of an adult in the population the early equations were fitted to. The eGFR is expressed per 1.73 m², not for the person's actual surface area.

Sources

• Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR Without Race. New England Journal of Medicine. 2021;385(19):1737-1749. doi:10.1056/NEJMoa2,102,953
• Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41. doi:10.1159/000180580
• Delgado C, Baweja M, Crews DC, et al. A Unifying Approach for GFR Estimation: Recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. American Journal of Kidney Diseases. 2022;79(2):268-288. doi:10.1053/j.ajkd.2021.08.003
• KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 2024;105(4S):S117-S314. doi:10.1016/j.kint.2023.10.018
• Young DS. Implementation of SI units for clinical laboratory data. Annals of Internal Medicine. 1987;106(1):114-129.
• National Institute of Standards and Technology. Special Publication 811, Guide for the Use of the International System of Units.