GFR Calculator
Estimate your Glomerular Filtration Rate (GFR) using the CKD-EPI formula. GFR is a key indicator of kidney function used in clinical settings to assess kidney health and stage chronic kidney disease. Results are for educational purposes only.
CKD-EPI Formula
GFR is calculated using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formula:
Scr = Serum Creatinine (mg/dL) · κ = 0.7 (female) or 0.9 (male) · α = -0.329 (female) or -0.411 (male)
Important Clinical Information
GFR is used to assess kidney function. Values below 60 mL/min/1.73 m² for three months or more may indicate chronic kidney disease. Always consult a healthcare professional for interpretation.
Your GFR Results
Calculation completeYour GFR Summary
Important Note About GFR
GFR is an estimate of kidney function. Single measurements should not be used alone for diagnosis. GFR can vary with age, gender, race, and other factors. Always consult a healthcare professional for interpretation.
How Your GFR Result Affects You
Personalized Recommendations
- Based on your GFR, maintain regular check-ups with your healthcare provider.
| GFR (mL/min/1.73 m²) | Stage | Kidney Function |
|---|---|---|
| ≥ 90 | Stage 1 | Normal kidney function |
| 60 – 89 | Stage 2 | Mildly decreased |
| 45 – 59 | Stage 3a | Mild to moderate decrease |
| 30 – 44 | Stage 3b | Moderate to severe decrease |
| 15 – 29 | Stage 4 | Severely decreased |
| < 15 | Stage 5 | Kidney failure |
The CKD-EPI formula provides an approximation of GFR. Clinical decisions should always be made by qualified healthcare professionals based on comprehensive assessment.
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How This Calculator Works
This calculator uses the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formula, which is widely used in clinical settings:
GFR = 141 × min(Scr/κ, 1)α × max(Scr/κ, 1)-1.209 × 0.993Age × 1.018 (if female) × 1.159 (if Black)
Where:
Scr = Serum Creatinine (mg/dL)
κ = 0.7 (female) or 0.9 (male)
α = -0.329 (female) or -0.411 (male)
Measurement Transparency:
• Age affects GFR (GFR naturally declines with age)
• Gender affects GFR (females have different constants)
• Race affects GFR (Black individuals have a correction factor)
• Serum creatinine is the primary lab value used
The CKD-EPI formula is recommended by major nephrology organizations.
For a complete health assessment, combine with our BMI Calculator or Blood Pressure Calculator.
Real Examples
Limitations & Important Warnings
This calculator provides an educational estimate only. Important limitations include:
- • GFR is an estimate, not a direct measurement
- • Single measurements should not be used for diagnosis
- • GFR varies with age, gender, race, and other factors
- • Muscle mass, diet, and medications can affect creatinine
- • Always consult a healthcare professional for interpretation
References
The educational information on this page is based on established nephrology research.
- Levey AS, Stevens LA – CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration)
- National Kidney Foundation – KDOQI Clinical Practice Guidelines
- Kidney Disease: Improving Global Outcomes (KDIGO) – CKD Guidelines
References were selected from recognized nephrology sources and are reviewed periodically for accuracy.
Trust & Privacy
This calculator is based on the CKD-EPI formula and is intended for educational purposes only.
Editorial Process
The CalculatorKits editorial team reviews this calculator periodically. Review includes:
- • Formula accuracy
- • Medical references
- • Educational content
- • User guidance
Last reviewed: July 2026
Frequently Asked Questions
GFR (Glomerular Filtration Rate) measures how well your kidneys are filtering waste from your blood. It's a key indicator of kidney function.
A normal GFR is typically ≥ 90 mL/min/1.73 m². GFR naturally decreases with age, so lower values may be normal in older adults.
The CKD-EPI formula is a widely used equation to estimate GFR from serum creatinine, age, gender, and race. It's more accurate than older formulas.
If your GFR is below 60 mL/min/1.73 m², or if you have risk factors for kidney disease, consult a healthcare professional for comprehensive evaluation.
No. This calculator provides an educational estimate. Diagnosis requires clinical evaluation by a healthcare professional.
📍 © 2026 CalculatorKits — GFR Calculator · For educational use only
GFR Calculator: Estimate Your Glomerular Filtration Rate
Kidney health is often discussed through laboratory numbers, and one of the most useful is the estimated glomerular filtration rate, commonly called eGFR. A GFR Calculator can help you understand how a GFR estimate is produced from information such as age, sex, and serum creatinine.
The result can be useful when you are reading a laboratory report or learning how kidney function is estimated. However, eGFR is an estimate, not a direct measurement of how much blood your kidneys filter. It also should not be used by itself to diagnose chronic kidney disease.
There is an important technical point for users of the CalculatorKits tool. The current CalculatorKits page identifies the CKD EPI method and displays an older equation that includes a race adjustment. Current guidance from NIDDK and the National Kidney Foundation recommends the 2021 CKD EPI equations without a race variable for adults.
That difference matters, especially when a result could influence a medical decision.
Quick Answer
A GFR Calculator estimates glomerular filtration rate, an important indicator of kidney function. The result is usually reported as mL/min/1.73 m².
A common modern adult equation uses:
- Serum creatinine
- Age
- Sex
The current NIDDK recommended adult CKD EPI creatinine equation from 2021 does not use race:
eGFR = 142 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^−1.200 × 0.9938^Age × 1.012 if female
Here, SCr means standardized serum creatinine, κ is 0.7 for females and 0.9 for males, and α is −0.241 for females and −0.302 for males.
An eGFR of 90 or higher is in the G1 range, 60 to 89 is G2, 45 to 59 is G3a, 30 to 44 is G3b, 15 to 29 is G4, and below 15 is G5. These are GFR categories, not complete diagnoses. G1 and G2 alone do not establish chronic kidney disease when there is no other evidence of kidney damage.
What Is a GFR Calculator?
A GFR Calculator is a tool that estimates your glomerular filtration rate from readily available health information and laboratory results.
GFR refers to the amount of fluid filtered by the kidneys over time. It is one of the main measures used to assess kidney function.
In everyday healthcare, clinicians usually work with estimated GFR, or eGFR, because directly measuring GFR requires specialized testing and is not practical for routine use. The National Kidney Foundation describes measured GFR as the best direct way to assess filtration, while eGFR is the practical estimate used in routine care.
The CalculatorKits tool is designed to make the calculation easier to understand. Its current interface asks for age, gender, race, serum creatinine, and a calculation date. It then produces an estimated GFR, a kidney function category, a CKD stage, and additional educational information.
Because kidney function is a medical topic, however, the number should always be interpreted in context.
Why Is GFR Important?
Your kidneys continuously filter blood and help remove waste products, regulate fluid balance, and maintain the right levels of minerals and electrolytes.
When kidney filtration becomes persistently reduced, waste products can accumulate and kidney disease may progress.
A GFR estimate helps healthcare professionals assess kidney function and monitor changes over time. It can also be used together with urine testing, especially the urine albumin to creatinine ratio, or uACR.
The current KDIGO guideline classifies chronic kidney disease using three dimensions:
Cause
GFR category
Albuminuria category
This approach is more informative than looking at eGFR alone.
That is one of the most important ideas to understand before relying on a GFR Calculator.
How Does a GFR Calculator Work?
The calculation uses a mathematical equation developed from research comparing measured kidney filtration with laboratory and demographic information.
Serum creatinine is particularly important.
Creatinine is produced as part of normal muscle metabolism and is cleared from the blood by the kidneys. When filtration falls, blood creatinine often rises.
The relationship is not perfectly direct, though. Creatinine is also influenced by muscle mass, diet, some medications, and other factors. NIDDK notes that these non GFR factors can affect how accurately creatinine based equations estimate kidney function.
The equation combines creatinine with age and sex to produce a standardized eGFR value.
The important word is estimated.
An eGFR is not the same as a direct measurement of filtration.
How to Use the GFR Calculator
The CalculatorKits tool follows a simple input process.
1. Enter your age
Enter your age in years.
The current CalculatorKits interface accepts ages from 1 to 120, but the CKD EPI adult equations described by NIDDK are intended for adults age 18 and older. Children require age appropriate equations, so this general adult calculator should not be used as the sole method for estimating kidney function in children.
2. Select your gender
Choose the gender option provided by the calculator.
Sex is part of the CKD EPI equation because different constants are used for males and females.
The scientific terminology in the equations refers to sex, while the CalculatorKits interface currently labels the field as gender.
3. Select the race option shown by the tool
The current CalculatorKits page includes a race field because the equation displayed on the live page contains a historical race adjustment.
This is an important point for anyone using the result today.
Current NIDDK and National Kidney Foundation guidance recommends the 2021 CKD EPI equations without a race variable for adult eGFR reporting.
For clinical decisions, use the eGFR reported by your laboratory or the equation recommended by your healthcare professional rather than relying on an older race adjusted online calculation.
4. Enter your serum creatinine
Find the serum creatinine value on your laboratory report.
CalculatorKits requests creatinine in mg/dL and currently accepts values from 0.1 to 20 mg/dL.
Enter the laboratory value carefully.
Do not substitute another kidney test or guess the creatinine value.
5. Select the calculation date
Enter or confirm the date associated with the calculation.
This can be useful when keeping a record of kidney function results over time.
6. Click Calculate GFR
Select Calculate GFR.
The calculator displays your estimated GFR and related information.
Use the number as an educational reference, not as a diagnosis.
How We Calculate GFR
This section is especially important because the formula on the live CalculatorKits page and current clinical recommendations are not identical.
The formula currently displayed by CalculatorKits
The live CalculatorKits page currently displays this CKD EPI equation:
GFR = 141 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.209 × 0.993^Age × 1.018 if female × 1.159 if Black
The page defines serum creatinine in mg/dL, uses different constants for males and females, and includes a Black race correction.
This is an older form of the CKD EPI equation.
The current 2021 CKD EPI creatinine equation
NIDDK and the National Kidney Foundation currently recommend the 2021 CKD EPI creatinine equation for adult eGFR estimation. It removes the race coefficient.
The current equation is:
eGFR = 142 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^−1.200 × 0.9938^Age × 1.012 if female
The constants are:
κ = 0.7 for females
κ = 0.9 for males
α = −0.241 for females
α = −0.302 for males
The result is reported as mL/min/1.73 m².
This distinction should be understood before using any online GFR tool for a medical decision.
What Does eGFR Measure?
eGFR is an estimate of how well the kidneys are filtering blood.
A higher value generally indicates greater filtration, while a lower value can indicate reduced kidney function.
However, eGFR naturally changes with age, and a lower value does not automatically mean that someone has chronic kidney disease.
For example, KDIGO classifies eGFR from 60 to 89 as G2, but G2 alone does not meet the criteria for chronic kidney disease when there is no evidence of kidney damage.
This is a common source of confusion on calculator pages.
A person should not see an eGFR of 75 and automatically conclude that they have kidney disease.
The number needs to be interpreted with urine albumin, previous results, age, medical history, and other findings.
Understanding GFR Categories
Current KDIGO categories are:
| GFR category | eGFR range in mL/min/1.73 m² | Description |
|---|---|---|
| G1 | 90 or higher | Normal or high |
| G2 | 60 to 89 | Mildly decreased |
| G3a | 45 to 59 | Mildly to moderately decreased |
| G3b | 30 to 44 | Moderately to severely decreased |
| G4 | 15 to 29 | Severely decreased |
| G5 | Below 15 | Kidney failure |
These categories describe GFR level. They do not by themselves establish chronic kidney disease. In particular, G1 and G2 require other evidence of kidney damage to meet the CKD definition.
GFR and Albuminuria
A GFR Calculator provides only the GFR side of kidney assessment.
Urine albumin is another major part of the picture.
KDIGO divides albuminuria into:
A1: below 30 mg/g
A2: 30 to 299 mg/g
A3: 300 mg/g or higher
A person can have an eGFR above 60 and still have chronic kidney disease if there is persistent evidence of kidney damage, such as significant albuminuria.
This is why an eGFR result should not be viewed as a complete kidney health report.
What Does Serum Creatinine Have to Do With GFR?
Serum creatinine is one of the main laboratory measurements used in creatinine based eGFR equations.
Creatinine comes from normal muscle metabolism and is removed from the bloodstream through the kidneys.
If kidney filtration decreases, creatinine often increases.
But there is an important catch.
A person with more muscle may naturally produce more creatinine. A person with very low muscle mass may produce less.
Diet, certain medicines, and other factors can also influence creatinine without representing a true change in filtration.
NIDDK recommends using standardized creatinine values with the appropriate eGFR equation because the accuracy of the estimate depends partly on the laboratory measurement.
Why Can Two GFR Calculators Give Different Results?
Different GFR Calculator results do not automatically mean one calculator is broken.
The underlying equation may be different.
For example, an older CKD EPI equation may produce a somewhat different result from the 2021 CKD EPI equation.
Other possibilities include different creatinine values, different age inputs, rounding differences, or differences in how the equation is implemented.
The National Kidney Foundation notes that for many patients, the 2021 equation produces similar values to older equations, but some results can differ by more than 10 percent, particularly at higher eGFR values and younger adult ages.
This is another reason to avoid comparing numbers from different calculators without checking the method.
Worked GFR Calculation Examples
The CalculatorKits page currently provides several examples based on its displayed equation.
Example 1: Higher estimated GFR
Age: 40
Serum creatinine: 0.9 mg/dL
Using the displayed CalculatorKits method, the result is approximately:
95 mL/min/1.73 m²
The CalculatorKits page places this in its normal kidney function example.
Remember that a value above 90 does not by itself prove that everything about kidney health is normal.
Example 2: Mildly decreased estimate
Age: 65
Serum creatinine: 1.2 mg/dL
The CalculatorKits example produces approximately:
72 mL/min/1.73 m²
That falls within the G2 range under current KDIGO classification. However, G2 alone does not establish CKD without evidence of kidney damage.
Example 3: Lower estimated GFR
Age: 55
Serum creatinine: 2.5 mg/dL
The CalculatorKits example produces approximately:
28 mL/min/1.73 m²
That falls within the current G4 range.
A result in this range deserves professional medical interpretation rather than relying on an online calculator alone.
These examples are mathematical illustrations, not predictions about actual patients.
Can GFR Change Over Time?
Yes.
eGFR can change because kidney function changes, but individual results can also vary because serum creatinine itself changes.
An illness, changes in hydration, medications, muscle activity, and other factors may influence creatinine and therefore the estimated GFR.
This is why healthcare professionals often look at trends rather than treating one result as definitive.
For someone with kidney disease, keeping a record of eGFR and urine albumin results can make it easier to identify meaningful changes.
The National Kidney Foundation specifically encourages tracking GFR and albuminuria over time.
Does Age Affect GFR?
Yes.
GFR generally declines with age, which is one reason age is part of the eGFR equation.
This does not mean that every lower eGFR in an older adult is harmless.
Instead, age is one part of the interpretation.
A 70 year old and a 25 year old with the same serum creatinine can have different eGFR estimates because the equation accounts for age.
Current CKD assessment still depends on the complete clinical picture rather than age alone.
Is a GFR Below 60 Always Kidney Disease?
Not necessarily from a single measurement.
KDIGO defines chronic kidney disease as abnormalities of kidney structure or function that are present for at least three months and have implications for health.
One route is an eGFR below 60 for at least three months.
Another is evidence of kidney damage, such as albuminuria, that persists for at least three months.
So if an online calculator gives you an eGFR of 55, that result does not by itself prove that you have CKD.
A healthcare professional may review previous results, repeat testing, check urine albumin, and investigate possible causes.
Who Should Be Careful With a General GFR Calculator?
A general online calculator may be less appropriate as a stand alone estimate in certain situations.
Extra care may be needed with:
- Very low or very high muscle mass
- Amputation
- Major changes in diet
- Certain medications
- Acute illness
- Pregnancy
- Children
- Rapidly changing kidney function
- People close to a clinical decision threshold
NIDDK notes that both creatinine and cystatin C can be used to estimate GFR and that the combined creatinine and cystatin C equation is more accurate than creatinine alone in many situations. It can be particularly useful when the estimate is close to an important clinical decision point.
This is one reason a laboratory reported eGFR may be more appropriate for clinical care than a general online calculation.
GFR Calculator and Medication Decisions
This point deserves special attention.
Do not use an online GFR Calculator to decide whether to start, stop, or change a medication.
Some medicines require kidney function to be considered when dosing, but the appropriate calculation may depend on the medication and clinical situation.
The National Kidney Foundation notes that drug dosing decisions should generally use a body surface area adjusted eGFR value expressed in mL/min rather than simply relying on the standardized eGFR value in mL/min/1.73 m².
That distinction is easy to miss.
If medication dosing is involved, follow the calculation and guidance used by your healthcare professional or pharmacist.
Common Mistakes When Using a GFR Calculator
Entering the wrong creatinine value
Always use the serum creatinine value from the relevant laboratory report.
Mixing units
The CalculatorKits tool asks for creatinine in mg/dL. Do not enter a value reported in µmol/L without converting it correctly.
NIDDK lists a conversion of creatinine from µmol/L to mg/dL by dividing by 88.4.
Assuming one result proves CKD
Chronic kidney disease requires persistence or other evidence of kidney damage.
Ignoring albuminuria
GFR is only one dimension of kidney assessment.
Comparing different equations without checking them
An older equation and a newer equation can produce different results.
Using an online result for medication dosing
Clinical decisions should not be based on a general online calculator.
Treating a normal result as proof that everything is fine
Kidney health involves more than GFR.
Accuracy and Limitations
The mathematical calculation can be performed accurately, but the result is still an estimate.
Several sources of uncertainty exist. The creatinine measurement itself has limitations.
The equation is a population based prediction rather than a direct measurement.
Individual muscle mass and diet can influence creatinine.
Acute changes in kidney function can make creatinine based estimates less reliable.
The equation used by a website may also be outdated.
This last point is particularly important for the current CalculatorKits tool. The live page displays the older CKD EPI equation with a race adjustment, while current NIDDK and National Kidney Foundation recommendations use the 2021 CKD EPI equations without race.
For an educational calculation, that distinction can be explained transparently. For clinical decisions, use the current equation reported by your laboratory or recommended by your healthcare professional.
When Should You Talk to a Healthcare Professional?
Discuss your kidney test results with a healthcare professional when:
- Your eGFR is repeatedly below 60
- Your urine albumin is elevated
- Your eGFR is falling over time
- You have diabetes or high blood pressure
- You have a history of kidney disease
- You have a family history of kidney disease
- Your laboratory report contains an unexpected result
- You have symptoms or other health concerns
People with diabetes and hypertension are among those who commonly need kidney screening because these conditions can increase the risk of chronic kidney disease.
If your laboratory report already includes an eGFR, use that value as the starting point for discussion rather than replacing it with a different online calculation.
Frequently Asked Questions
What is a GFR Calculator?
A GFR Calculator estimates glomerular filtration rate using information such as age, sex, and serum creatinine. It provides an estimated kidney filtration value rather than directly measuring GFR.
What is a normal GFR?
An eGFR of 90 or higher falls within the G1 category. However, G1 alone does not guarantee that there is no kidney disease, and lower GFR values can also occur without CKD when there is no other evidence of kidney damage.
What does eGFR mean?
eGFR means estimated glomerular filtration rate. It is an estimate of kidney filtration based on a mathematical equation and laboratory measurements.
What creatinine level is used for eGFR?
Creatinine is measured from a blood sample. The result is entered into an appropriate eGFR equation along with age and sex.
Is eGFR the same as measured GFR?
No. eGFR is calculated from an equation, while measured GFR requires specialized testing. Measured GFR is more direct but is not practical for routine use.
Can GFR improve?
Yes, an eGFR value can change over time. Improvement can occur when a temporary factor affecting kidney function or creatinine is resolved, although the explanation depends on the underlying cause.
Is a GFR below 60 kidney disease?
A single result below 60 does not automatically establish chronic kidney disease. CKD requires reduced GFR or another marker of kidney damage that persists for at least three months.
Why is my GFR different on another website?
Different websites may use different CKD EPI versions, creatinine values, rounding rules, or other assumptions. Current and older equations can also produce different estimates.
Does race affect the current eGFR equation?
Current recommended adult CKD EPI equations do not use a race coefficient. NIDDK and the National Kidney Foundation recommend the 2021 equations without race.
Can I use a GFR Calculator to adjust medication?
No. Do not change medication dosage based on an online calculator. Medication related kidney function decisions should be made using the appropriate clinical method and professional guidance.
Key Takeaways
A GFR Calculator provides an estimate of kidney filtration from information such as age, sex, and serum creatinine.
The result is usually expressed in mL/min/1.73 m² and is useful for understanding kidney function.
Current KDIGO categories range from G1 at 90 or higher to G5 below 15. However, an eGFR category alone does not diagnose chronic kidney disease.
The CalculatorKits page currently displays an older CKD EPI equation that includes a race factor. Current NIDDK and National Kidney Foundation guidance recommends the 2021 CKD EPI equations without race for adults.
Creatinine, age, sex, muscle mass, medications, diet, and other factors can affect the estimate.
Urine albumin is also important when assessing kidney health.
Do not use a calculator result to diagnose CKD or change medication.
For clinical decisions, use current laboratory reported eGFR and professional medical interpretation.
Related Health Tools
Blood Pressure Calculator
Review systolic and diastolic blood pressure readings and understand the general adult blood pressure categories. Blood pressure is closely relevant to kidney health because hypertension is an important CKD risk factor.
Blood Sugar Calculator
Review common fasting, post meal, random glucose, and HbA1c results. Blood glucose is relevant to kidney health because diabetes is a major risk factor for chronic kidney disease.
Body Surface Area Calculator
Estimate body surface area using height and weight. BSA can be relevant in some clinical calculations and is distinct from the standardized 1.73 m² body surface area used for reporting eGFR.
BMI Calculator
Calculate BMI from height and weight and review the standard adult BMI categories as another general health measurement.
References
- National Institute of Diabetes and Digestive and Kidney Diseases, eGFR Equations for Adults
Provides the current 2021 CKD EPI equations for adults, including the creatinine equation and the combined creatinine and cystatin C equation.
NIDDK: eGFR Equations for Adults - National Kidney Foundation, CKD EPI Creatinine Equation 2021
Explains the current adult equation, its constants, units, and clinical use without a race coefficient.
National Kidney Foundation: CKD EPI Creatinine Equation - National Kidney Foundation, eGFR Calculator
Explains eGFR, current clinical use, CKD assessment, albuminuria, and the distinction between standardized and body surface area adjusted values.
National Kidney Foundation: eGFR Calculator - KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease
Provides the current GFR and albuminuria categories and explains that chronic kidney disease requires abnormalities to persist for at least three months.
KDIGO 2024 CKD Guideline - National Kidney Foundation, Recommendations for Implementing the 2021 CKD EPI Equation
Explains the transition from older equations to the 2021 equation without race and discusses differences between older and newer eGFR estimates.
National Kidney Foundation: 2021 CKD EPI Implementation Guidance - NIDDK, Identifying and Evaluating Patients With Chronic Kidney Disease
Explains the role of eGFR, urine albumin testing, and persistence when evaluating chronic kidney disease.
NIDDK: Evaluate Chronic Kidney Disease
Medical Disclaimer
This article and the CalculatorKits GFR Calculator are provided for general educational purposes only. A GFR or eGFR result is an estimate of kidney filtration and does not by itself diagnose chronic kidney disease or determine treatment. Kidney health assessment may also require urine albumin testing, repeat measurements, medical history, and other laboratory or clinical information. Do not use an online calculator to change medication or make treatment decisions. If you have an abnormal kidney test result or concerns about kidney health, discuss them with a qualified healthcare professional.
Written and reviewed by the CalculatorKits Editorial Team
Last Updated: September 6, 2026