# What is my GFR?

Estimates glomerular filtration rate (eGFR) for adults from serum creatinine, cystatin C, or both, with the race-free 2021 CKD-EPI equations, and shows the KDIGO GFR category.

- Page: https://www.acalculator.org/health/gfr-calculator
- JSON spec: https://www.acalculator.org/health/gfr-calculator.json
- Version: d91c19c77935

## Default answer

Example with the default inputs (Equation Creatinine (CKD-EPI 2021), Creatinine units mg/dL, Serum creatinine (mg/dL) 1, Age 50, Sex Male): Your estimated GFR is 92 mL/min/1.73 m², KDIGO category G1: normal or high.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| eq | Equation | Which CKD-EPI equation: creatinine only, creatinine with cystatin C, or cystatin C only. |
| units | Creatinine units | US units (mg/dL) or SI units (µmol/L) for serum creatinine. |
| scr | Serum creatinine (mg/dL) | Serum creatinine from the blood test, in mg/dL (IDMS-standardized, as labs report it). |
| scrSi | Serum creatinine (µmol/L) | Serum creatinine from the blood test, in µmol/L. |
| cys | Cystatin C (mg/L) | Serum cystatin C from the blood test, in mg/L (standardized to the IFCC reference material). |
| age | Age | Age in whole years. The equations are for adults 18 and older. |
| sex | Sex | Sex at birth, which the equations use. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| egfr | Estimated GFR | eGFR in mL/min/1.73 m², rounded to a whole number as labs report it. |
| stage | KDIGO GFR category | The KDIGO 2012 GFR category (G1 to G5) for the whole-number eGFR. |
| scrOther | Creatinine in the other unit | The creatinine you entered, converted with 1 mg/dL = 88.4 µmol/L. |

## Method

CKD-EPI 2021 creatinine: 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age × 1.012 (women), κ 0.7 (women) or 0.9 (men), α −0.241 (women) or −0.302 (men); CKD-EPI 2021 creatinine-cystatin C and 2012 cystatin C as stated in content.mdx. Scr in mg/dL, Scys in mg/L.

## Assumptions

- Adults 18 and older with stable kidney function (not acute kidney injury).
- Creatinine is IDMS-standardized and cystatin C is standardized to the IFCC reference material. µmol/L is converted with 1 mg/dL = 88.4 µmol/L.
- The equations do not use race (Inker 2021; NKF-ASN Task Force 2021).
- eGFR is per 1.73 m² of body surface area and is rounded to a whole number; the KDIGO category is read from the whole number.

## Worked examples

1. eq = cr, units = us, scr = 1, age = 50, sex = male gives egfr = 92, stage = G1: normal or high. Source: Inker et al., N Engl J Med 2021 (CKD-EPI 2021 creatinine): 142 × (1.0/0.9)^−1.200 × 0.9938^50 = 91.69, shown as 92.
2. eq = cr, units = si, scrSi = 132.6, age = 70, sex = female gives egfr = 37, stage = G3b: moderately to severely decreased, scrOther = 1.50 mg/dL. Source: Inker et al. 2021: 132.6 ÷ 88.4 = 1.5 mg/dL.
3. eq = cr-cys, units = us, scr = 1.2, cys = 1.1, age = 60, sex = male gives egfr = 71, stage = G2: mildly decreased. Source: Inker et al. 2021 (creatinine-cystatin C): 135 × (1.2/0.9)^−0.544 × (1.1/0.8)^−0.778 × 0.9961^60 = 71.28, shown as 71.
4. eq = cys, cys = 1.4, age = 45, sex = female gives egfr = 49, stage = G3a: mildly to moderately decreased. Source: Inker et al., N Engl J Med 2012 (CKD-EPI cystatin C): 133 × (1.4/0.8)^−1.328 × 0.996^45 × 0.932 = 49.22, shown as 49.

## FAQ

### What is GFR?

Glomerular filtration rate (GFR) is the volume of blood plasma that the kidneys filter each minute. It is the best overall measure of kidney function. Measuring it directly needs a special test, so labs estimate it (eGFR) from a blood marker, age, and sex.

### Which equation does this GFR calculator use?

By default, the 2021 CKD-EPI creatinine equation (Inker and others, 2021). You can also pick the 2021 creatinine-cystatin C equation or the 2012 cystatin C equation. The National Kidney Foundation and the American Society of Nephrology recommend these race-free equations for adults in the US.

### What is a normal eGFR?

KDIGO calls an eGFR of 90 or more "normal or high" (G1) and 60 to 89 "mildly decreased" (G2). Below 60 for 3 months or more meets the definition of chronic kidney disease. eGFR falls slowly with age, so a value in the 60s can be common in older adults.

### Why does the result say mL/min/1.73 m²?

The equations give GFR scaled to a standard body surface area of 1.73 m², so results can be compared between people of different sizes. Drug labels sometimes use creatinine clearance in mL/min instead; see the creatinine clearance calculator for Cockcroft-Gault.

### When is cystatin C used?

Creatinine depends on muscle mass and diet. Cystatin C does not, so KDIGO suggests adding it when a creatinine-based eGFR may be wrong, for example with very high or low muscle mass, or to confirm chronic kidney disease. The combined creatinine-cystatin C equation is the most accurate of the three.

### Can I use this for children or during pregnancy?

No. These equations were built and tested in adults 18 and older who were not pregnant. Children need a pediatric equation, and pregnancy changes kidney filtration.

## Sources

- Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C-based equations to estimate GFR without race. N Engl J Med. 2021;385(19):1737-1749. https://doi.org/10.1056/NEJMoa2102953 (retrieved 2026-09-28)
- Inker LA, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20-29. https://doi.org/10.1056/NEJMoa1114248 (retrieved 2026-09-28)
- 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. Am J Kidney Dis. 2022;79(2):268-288. https://doi.org/10.1053/j.ajkd.2021.08.003 (retrieved 2026-09-28)
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl. 2013;3(1):1-150. https://kdigo.org/guidelines/ckd-evaluation-and-management/ (GFR categories G1 to G5; 1 mg/dL creatinine = 88.4 µmol/L; retrieved 2026-09-28)