# GFR calculator (eGFR, CKD-EPI 2021)

> eGFR from serum creatinine (mg/dL or µmol/L), age and sex by the race-free CKD-EPI 2021 equation, with optional cystatin C and the KDIGO G1–G5 stage.

Interactive version: https://www.calcopenly.com/health/gfr-calculator
Subject: Health and fitness calculators

Estimated glomerular filtration rate (eGFR) is the volume of blood plasma the kidneys filter each minute, scaled to a body surface area of 1.73 m². It is calculated from serum creatinine, age and sex with the 2021 CKD-EPI equation, which dropped the race coefficient of the 2009 version; the National Kidney Foundation and the American Society of Nephrology recommend it for adults in the US. With a cystatin C result the 2021 creatinine–cystatin C equation is also computed, and KDIGO 2024 grades the kidneys on that combined value when it is available.

Clinicians use eGFR to stage chronic kidney disease and to adjust drug doses. A 50-year-old man with a creatinine of 1.0 mg/dL (88 µmol/L) has an eGFR of 92, category G1. An eGFR below 60 for more than 3 months is chronic kidney disease, category G3a or worse.

The equations assume creatinine is stable. They read wrong in acute kidney injury, pregnancy, very high or low muscle mass, and after a meat-heavy meal or creatine supplements.

## Inputs

- **Serum creatinine**: Standardized (IDMS-traceable) value from a blood test.
- **Creatinine unit** (options: mg/dL, µmol/L)
- **Age**: The CKD-EPI equations are validated for adults aged 18 and over.
- **Sex (for the formula)** (options: Male, Female)
- **Serum cystatin C (optional)**: Adds the 2021 creatinine–cystatin C and 2012 cystatin C equations.
- **Urine albumin-to-creatinine ratio (optional)**: Adds the KDIGO albuminuria category and heat-map risk.
- **ACR unit** (options: mg/g, mg/mmol)

## Results

- eGFR (creatinine, CKD-EPI 2021) (mL/min/1.73 m²) — main result
- eGFR (creatinine–cystatin C, 2021) (mL/min/1.73 m²)
- eGFR (cystatin C only, 2012) (mL/min/1.73 m²)
- GFR category (KDIGO 2024)
- Albuminuria category
- KDIGO heat-map risk
- Creatinine in the other unit (mg/dL)
- Creatinine in the other unit (µmol/L)

## Formula

$$
\text{eGFR}_{cr} = 142 \times \min\!\left(\tfrac{S_{cr}}{\kappa},1\right)^{\alpha} \times \max\!\left(\tfrac{S_{cr}}{\kappa},1\right)^{-1.200} \times 0.9938^{\text{age}} \times 1.012\ [\text{female}]
$$

## Worked examples

### Man, 50 years, creatinine 1.0 mg/dL

- Serum creatinine: 1.0
- Creatinine unit: mg/dL
- Age: 50 years
- Sex (for the formula): Male
- **eGFR (creatinine, CKD-EPI 2021): 92 mL/min/1.73 m²**
- **GFR category (KDIGO 2024): G1: normal or high**
- **Creatinine in the other unit: 88 µmol/L**
- **Creatinine in the other unit: not applicable**
- Checked against: Python 3.8 decimal: 142 × (1.0/0.9)^−1.200 × 0.9938^50 = 91.691 (NKF 2021 CKD-EPI creatinine equation); 1.0 × 88.4 = 88.40 µmol/L

### Woman, 60 years, creatinine 0.8 mg/dL

- Serum creatinine: 0.8
- Creatinine unit: mg/dL
- Age: 60 years
- Sex (for the formula): Female
- **eGFR (creatinine, CKD-EPI 2021): 84 mL/min/1.73 m²**
- **GFR category (KDIGO 2024): G2: mildly decreased**
- Checked against: Python 3.8 decimal: 142 × (0.8/0.7)^−1.200 × 0.9938^60 × 1.012 = 84.298

### Man, 70 years, creatinine 177 µmol/L

- Serum creatinine: 177
- Creatinine unit: µmol/L
- Age: 70 years
- Sex (for the formula): Male
- **eGFR (creatinine, CKD-EPI 2021): 35 mL/min/1.73 m²**
- **GFR category (KDIGO 2024): G3b: moderately to severely decreased**
- **Creatinine in the other unit: 2.00 mg/dL**
- **Creatinine in the other unit: not applicable**
- Checked against: Python 3.8 decimal: 177 / 88.4 = 2.00226 mg/dL; 142 × (2.00226/0.9)^−1.200 × 0.9938^70 = 35.195

### Woman, 45 years, creatinine 0.6 mg/dL, cystatin C 0.9 mg/L

- Serum creatinine: 0.6
- Creatinine unit: mg/dL
- Age: 45 years
- Sex (for the formula): Female
- Serum cystatin C (optional): 0.9 mg/L
- **eGFR (creatinine, CKD-EPI 2021): 113 mL/min/1.73 m²**
- **eGFR (creatinine–cystatin C, 2021): 103 mL/min/1.73 m²**
- **eGFR (cystatin C only, 2012): 89 mL/min/1.73 m²**
- **GFR category (KDIGO 2024): G1: normal or high**
- Checked against: Python 3.8 decimal: eGFRcr = 142 × (0.6/0.7)^−0.241 × 0.9938^45 × 1.012 = 112.735; eGFRcr-cys = 135 × (0.6/0.7)^−0.219 × (0.9/0.8)^−0.778 × 0.9961^45 × 0.963 = 102.910; eGFRcys = 133 × (0.9/0.8)^−1.328 × 0.996^45 × 0.932 = 88.513

### Edge: creatinine exactly at κ (woman, 0.7 mg/dL, 40 years)

- Serum creatinine: 0.7
- Creatinine unit: mg/dL
- Age: 40 years
- Sex (for the formula): Female
- **eGFR (creatinine, CKD-EPI 2021): 112 mL/min/1.73 m²**
- Checked against: Python 3.8 decimal: both the min and max terms equal 1, so eGFR = 142 × 0.9938^40 × 1.012 = 112.054

### Boundary: 59.86 is reported as 60, category G2

- Serum creatinine: 1.32
- Creatinine unit: mg/dL
- Age: 65 years
- Sex (for the formula): Male
- **eGFR (creatinine, CKD-EPI 2021): 60 mL/min/1.73 m²**
- **GFR category (KDIGO 2024): G2: mildly decreased**
- **Albuminuria category: not applicable**
- Checked against: Python 3.8 decimal: 142 × (1.32/0.9)^−1.200 × 0.9938^65 = 59.858; KDIGO 2024 Table 11 reports eGFR as a whole number (60), and G2 is 60–89

## Questions

### What is a normal eGFR?

90 mL/min/1.73 m² or higher is KDIGO category G1, normal or high, and 60 to 89 is G2, mildly decreased. Neither counts as chronic kidney disease unless there is also kidney damage, such as albumin in the urine, lasting at least 3 months. The equation lowers eGFR by 0.62 % for each year of age, so the same creatinine of 1.0 mg/dL gives a man 92 at age 50 and 81 at age 70.

### What eGFR indicates kidney disease?

An eGFR below 60 mL/min/1.73 m² that lasts more than 3 months meets the KDIGO 2024 definition of chronic kidney disease on its own. KDIGO grades it G3a (45–59), G3b (30–44), G4 (15–29) and G5, kidney failure (below 15). A single low reading is not a diagnosis, because acute illness, dehydration or a recent large meat meal can lower eGFR temporarily; KDIGO asks for repeat testing to confirm.

### Why was race removed from the eGFR equation?

The 2009 CKD-EPI equation multiplied eGFR by 1.159 for Black patients, a coefficient based on race as a social category. A joint National Kidney Foundation and American Society of Nephrology task force recommended in 2021 that US labs switch to the refitted 2021 equation, which uses creatinine, age and sex only. KDIGO 2024 practice point 1.2.4.2 says race should not be used to compute eGFR.

### When should cystatin C be used to estimate GFR?

When creatinine is likely to mislead. KDIGO 2024 Table 8 lists eating disorders, bodybuilding, above-knee amputation, spinal cord injury, vegetarian or high-protein diets and creatine supplements, among others. KDIGO recommends that when cystatin C is available the GFR category be taken from the combined creatinine–cystatin C equation, which is closer to measured GFR than either marker alone. A large gap between eGFRcr and eGFRcys is itself a signal that one of them is off.

### How do you convert creatinine from µmol/L to mg/dL?

Divide by 88.4, the factor in the KDIGO 2024 conversion table; it is 10,000 divided by the molar mass of creatinine, 113.12 g/mol. A result of 88 µmol/L is 1.00 mg/dL and 150 µmol/L is 1.70 mg/dL. KDIGO asks labs to report creatinine to the nearest whole number in µmol/L and to two decimals in mg/dL.

### How accurate is the GFR calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 8 worked examples whose answers come from independent sources; for example, “Man, 50 years, creatinine 1.0 mg/dL” is checked against Python 3.8 decimal: 142 × (1.0/0.9)^−1.200 × 0.9938^50 = 91.691 (NKF 2021 CKD-EPI creatinine equation); 1.0 × 88.4 = 88.40 µmol/L.

### Where does the method come from?

Inker LA et al. New creatinine- and cystatin C–based equations to estimate GFR without race. N Engl J Med 2021;385:1737–1749; National Kidney Foundation — CKD-EPI creatinine equation (2021); National Kidney Foundation — CKD-EPI creatinine–cystatin C equation (2021); National Kidney Foundation — CKD-EPI cystatin C equation (2012); KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int 2024;105(4S):S117–S314; Delgado C et al. A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force. Am J Kidney Dis 2022;79:268–288.

## Sources

- [Inker LA et al. New creatinine- and cystatin C–based equations to estimate GFR without race. N Engl J Med 2021;385:1737–1749](https://doi.org/10.1056/NEJMoa2102953)
- [National Kidney Foundation — CKD-EPI creatinine equation (2021)](https://www.kidney.org/ckd-epi-creatinine-equation-2021)
- [National Kidney Foundation — CKD-EPI creatinine–cystatin C equation (2021)](https://www.kidney.org/ckd-epi-creatinine-cystatin-equation-2021)
- [National Kidney Foundation — CKD-EPI cystatin C equation (2012)](https://www.kidney.org/ckd-epi-cystatin-c-equation-2012)
- [KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int 2024;105(4S):S117–S314](https://kdigo.org/wp-content/uploads/2024/03/KDIGO-2024-CKD-Guideline.pdf)
- [Delgado C et al. A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force. Am J Kidney Dis 2022;79:268–288](https://doi.org/10.1053/j.ajkd.2021.08.003)

_Note: medical information, not professional advice._