GFR Calculator: Estimate Glomerular Filtration Rate & Kidney Function
Use this GFR Calculator to estimate your glomerular filtration rate (eGFR) from commonly used kidney-function equations. Enter serum creatinine, age and sex to calculate an estimated GFR, then compare results across additional equations where applicable.
The calculator includes the 2021 CKD-EPI creatinine equation, the 2021 CKD-EPI creatinine-cystatin C equation, the 2012 CKD-EPI cystatin C equation, and selected historical or clinical comparison equations. For children, the calculator can use the Bedside Schwartz equation when pediatric inputs are appropriate. NIDDK identifies the 2021 CKD-EPI equations as race-free adult equations and notes that using both creatinine and cystatin C can improve GFR estimation when clinically appropriate.
An eGFR result is an estimate rather than a direct measurement of filtration. Its interpretation depends on the equation used, laboratory measurements, age, body composition, urine albumin and the clinical context. Trends over time are often more informative than a single result.
1. What is GFR and eGFR?
Glomerular filtration rate (GFR) describes how quickly the kidneys filter fluid through the glomeruli. Because directly measuring GFR requires specialized clearance testing, routine clinical care generally uses estimated GFR (eGFR) calculated from biomarkers such as serum creatinine and, when available, cystatin C.
The result is commonly reported as:
The 1.73 m² represents a standardized body-surface-area reference. This allows kidney filtration estimates to be compared across people of different body sizes.
The important distinction is that eGFR is a calculated estimate, not a direct laboratory measurement of filtration. Equation performance also becomes less precise at higher GFR values.
2. How this GFR Calculator works
The calculator accepts the laboratory and demographic information required by the selected equation and then produces the corresponding eGFR.
For the current primary adult method, CKD-EPI 2021 creatinine, the equation is:
where:
- SCr = standardized serum creatinine in mg/dL
- κ = 0.7 for females and 0.9 for males
- α = -0.241 for females and -0.302 for males
- Age is measured in years
This equation does not use a race coefficient.
Creatinine unit conversion
When creatinine is supplied in SI units:
Thus: 0.9 mg/dL = 79.56 µmol/L. The calculator converts the laboratory value before applying the selected equation.
3. Why the calculator includes more than one GFR equation
Different estimating equations were developed for different populations, biomarkers and clinical purposes. They should therefore not be treated as interchangeable formulas that necessarily produce the same number.
This is the current race-free creatinine-based adult equation and is widely used for routine adult eGFR estimation. It uses age, sex and standardized serum creatinine.
This equation uses both serum creatinine and cystatin C:
NIDDK states that combined creatinine-cystatin C estimation is generally preferred when available because it can be more accurate than creatinine alone, particularly when the eGFR is close to an important clinical decision threshold.
This method estimates GFR using cystatin C rather than serum creatinine:
Cystatin C can provide useful additional information because it is influenced by different non-GFR determinants than creatinine.
4. eGFR and CKD stages
KDIGO categorizes GFR into six categories:
| GFR category | eGFR, mL/min/1.73 m² | Description |
|---|---|---|
| G1 | ≥90 | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | <15 | Kidney failure |
These are GFR categories, not automatically diagnoses of chronic kidney disease. KDIGO specifically notes that G1 and G2 do not meet CKD criteria in the absence of evidence of kidney damage. That distinction is important when interpreting a calculator result.
5. When does an eGFR result indicate CKD?
A single eGFR number does not by itself establish chronic kidney disease.
The National Kidney Foundation defines CKD as an abnormality of kidney structure or function that is present for more than three months and has implications for health. CKD can be established by either:
- eGFR <60 mL/min/1.73 m² for more than three months, or
- persistent evidence of kidney damage, such as albuminuria with ACR ≥30 mg/g, for more than three months.
Therefore, someone with an eGFR of 95 is not automatically considered to have CKD, and someone with an eGFR between 60 and 89 does not automatically have CKD either. Clinical interpretation requires the patient's history, repeat testing and other evidence of kidney damage.
6. eGFR and urine albumin: why both matter
Kidney function assessment is stronger when eGFR is considered alongside urine albumin-to-creatinine ratio (uACR/ACR).
KDIGO divides albuminuria into:
| Category | ACR |
|---|---|
| A1 | <30 mg/g |
| A2 | 30–300 mg/g |
| A3 | >300 mg/g |
The G category and A category are used together to describe CKD prognosis. Someone with the same eGFR can have a substantially different risk profile depending on the amount of albumin in the urine.
This is why the calculator's KDIGO risk grid combines eGFR categories with albuminuria categories rather than treating eGFR as the only kidney-health variable.
7. Why your eGFR can differ between equations
It is normal for two legitimate equations to produce somewhat different results.
The equations use different biomarkers and mathematical coefficients, and creatinine itself is affected by factors beyond filtration, including muscle mass and other non-GFR determinants. NIDDK notes that the 2021 creatinine equation has limitations and that combined creatinine-cystatin C estimation can reduce some of the uncertainty.
This is particularly relevant for people with unusual muscle mass, frailty or other conditions that make serum creatinine less representative of filtration. For these situations, the difference between equations is not necessarily evidence that one result is “wrong.”
8. eGFR versus Cockcroft-Gault creatinine clearance
This calculator also separates Cockcroft-Gault creatinine clearance (CrCl) from eGFR because they are not the same measurement.
Cockcroft-Gault estimates creatinine clearance in mL/min, whereas standard CKD-EPI eGFR is reported in mL/min/1.73 m².
The two values should not be compared as if they were identical. The distinction is particularly important when a medication reference or clinical protocol specifically calls for creatinine clearance rather than indexed eGFR. The National Kidney Foundation's clinical calculator also distinguishes BSA-adjusted eGFR from unindexed values used in medication-related decisions.
9. Pediatric eGFR
Adult equations should not simply be applied to children. For pediatric patients, this calculator can use the Bedside Schwartz equation:
The equation uses height and standardized serum creatinine and is intended for pediatric estimation. Your calculator therefore switches its population logic rather than treating a child's values as an adult CKD-EPI calculation. A mathematically valid result still needs pediatric clinical context; unusual supplied height or laboratory values can produce unusual estimates.
10. Example calculation
Consider an adult male aged 50 with:
- Serum creatinine = 0.9 mg/dL
- Height = 5 ft 10 in
- Weight = 160 lb
Using CKD-EPI 2021:
which produces an estimated GFR of approximately: 104 mL/min/1.73 m².
The independent Cockcroft-Gault calculation for the same profile is approximately: 100.8 mL/min.
Those values are both consistent with the corresponding equations and, importantly, they are expressed in different units and represent different estimation concepts. The supplied calculator regression independently verified these baseline values.
11. How to use the GFR Calculator
Use the value from your laboratory report and select the appropriate unit, either mg/dL or µmol/L.
Adult CKD-EPI equations use age and sex as part of the mathematical model.
Height and weight are not required by the CKD-EPI creatinine equation but are relevant for equations such as Cockcroft-Gault and pediatric formulas.
Cystatin C enables additional eGFR equations, while uACR allows a more complete KDIGO risk assessment.
Review the primary eGFR, formula comparison, G category and, where sufficient information is available, the KDIGO albuminuria/eGFR risk classification.
12. Why trends matter more than one isolated eGFR
An eGFR result is a point estimate with inherent uncertainty. NIDDK specifically notes that trends in eGFR are often more informative than a single value because repeated values help reveal whether kidney function is stable, declining or changing temporarily.
Changes in hydration, acute illness, laboratory variation and other non-GFR determinants can influence creatinine and therefore affect a creatinine-based eGFR. For that reason, a surprising result should be interpreted alongside previous results, urine testing and the broader clinical picture rather than in isolation.
13. Important limitations
This calculator provides estimated kidney filtration, not a direct measurement of GFR.
Results may be less reliable when the patient has characteristics that substantially affect serum creatinine or cystatin C independent of filtration. Equation accuracy also varies across populations and tends to become less precise at higher GFR values.
The calculator should not be used by itself to diagnose CKD, determine dialysis eligibility, change medication doses, assess transplant eligibility or make other high-stakes treatment decisions. Clinical decisions should use the laboratory result, the appropriate equation, repeat measurements, urine albumin testing and professional medical judgment.
14. Related Renal & Metabolic Calculators
Integrate your kidney filtration assessment with related physiological, body composition, and nutritional calculators:
15. Clinical Disclaimer & Recommended Source References
This calculator provides mathematical estimates based on published GFR equations. It is intended for educational and reference purposes and does not diagnose kidney disease or replace professional medical evaluation. eGFR must be interpreted in clinical context, including repeat measurements, urine albumin and other evidence of kidney damage when appropriate. Medication dosing, transplant evaluation, dialysis decisions and other treatment decisions should be made using applicable clinical guidance and a qualified healthcare professional.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK): eGFR equations for adults, including CKD-EPI 2021 creatinine, creatinine-cystatin C and cystatin C equations.
- National Kidney Foundation (NKF): CKD criteria and eGFR interpretation.
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease: GFR and albuminuria categories and CKD classification.
- National Kidney Foundation eGFR Calculator: clinical distinction between indexed eGFR and BSA-adjusted values and use of creatinine/cystatin C equations.