# Glomerular Filtration Rate Calculator (Creatinine and Cystatin C)

URL: https://speedycalculator.com/calculators/health/glomerular-filtration-rate/
Last updated: 2026-10-30

> The glomerular filtration rate calculator estimates GFR with the 2021 CKD-EPI equations using creatinine, cystatin C or both together – the combined equation is the most accurate – and gives the KDIGO GFR category.

## Inputs

- Sex
- Age (years)
- Serum creatinine (mg/dL, µmol/L)
- Cystatin C (0 if not measured) (mg/L)

## Results

- eGFR – creatinine
- eGFR – cystatin C
- eGFR – combined
- GFR category (combined)

## Formula

```
Creatinine: 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^−1.200 × 0.9938^age (× 1.012 women)
Cystatin C (2012): 133 × min(Scys/0.8,1)^−0.499 × max(Scys/0.8,1)^−1.328 × 0.996^age (× 0.932 women)
Combined (2021): 135 × min(Scr/κ,1)^α × max(Scr/κ,1)^−0.544 × min(Scys/0.8,1)^−0.323 × max(Scys/0.8,1)^−0.778 × 0.9961^age (× 0.963 women); α = −0.219 (women) or −0.144 (men)
```

## Explanation

Cystatin C is made by all cells at a steady rate and is less affected by muscle mass than creatinine. KDIGO recommends confirming an eGFR of 45–59 with cystatin C, and using the combined equation when an accurate GFR matters, such as for drug dosing.

### How to use the Glomerular Filtration Rate Calculator

- **Sex**
- **Age**
- **Serum creatinine**
- **Cystatin C (0 if not measured)**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter creatinine and, if available, cystatin C. Leave cystatin C at zero to use creatinine alone.

### GFR categories (KDIGO)

StageeGFR (mL/min/1.73 m²)DescriptionG190 or aboveNormal or highG260–89Mildly decreasedG3a45–59Mildly to moderately decreasedG3b30–44Moderately to severely decreasedG415–29Severely decreasedG5below 15Kidney failure

### Inputs explained

FieldWhat to enterSexChoose one: Male, FemaleAgeIn yearsSerum creatinineUnits: mg/dL, µmol/LCystatin C (0 if not measured)In mg/L
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Sex: Male; Age: 60 years; Serum creatinine: 1.1 mg/dL; Cystatin C (0 if not measured): 1 mg/L.

Results — eGFR – creatinine = 77 mL/min/1.73 m²; eGFR – cystatin C = 78 mL/min/1.73 m²; **eGFR – combined = 80 mL/min/1.73 m²**; GFR category (combined) = G2 – mildly decreased.

## Key terms

- **Cystatin C**: A small protein filtered by the kidneys, used as a GFR marker.

## FAQ

**Why use cystatin C?**
It is less affected by muscle mass, diet and race than creatinine.

**Which eGFR should I trust?**
The combined creatinine–cystatin C equation is the most accurate.

**Is cystatin C affected by anything?**
Thyroid disease, steroids, inflammation and obesity can raise it.


## Sources

- [Inker LA et al. New creatinine- and cystatin C–based equations to estimate GFR without race. N Engl J Med, 2021](https://pubmed.ncbi.nlm.nih.gov/34554658/)
- [KDIGO 2024 Clinical practice guideline for CKD](https://kdigo.org/guidelines/ckd-evaluation-and-management/)