What is a normal GFR?

A normal GFR is generally considered to be 90 mL/min/1.73m² or higher, though GFR naturally declines with age. For a healthy young adult, typical values range from 90–120 mL/min/1.73m².

In some cases, yes. Certain causes of kidney function decline (such as dehydration, urinary tract obstruction, or medication effects) are reversible with appropriate treatment. However, in chronic kidney disease, GFR loss is typically progressive.

What is the difference between CKD-EPI and MDRD?

CKD-EPI is a newer equation generally considered more accurate, especially at higher GFR values. MDRD was the standard for many years but tends to underestimate GFR in people with near-normal kidney function. The CKD-EPI equation is now recommended by most nephrology guidelines.

Do I need to fast before the test?

No fasting is required for a serum creatinine test. However, you should avoid eating large amounts of cooked meat before the test, as it can temporarily increase creatinine levels.

At what GFR level do symptoms appear?

Most people with CKD stages 1–3 do not experience noticeable symptoms. Symptoms such as fatigue, swelling, changes in urination, and shortness of breath typically do not appear until stage 4 or 5, when kidney function is severely reduced.

GFR Calculator

Age (years)

Serum Creatinine (mg/dL)

Gender

Introduction

The Glomerular Filtration Rate (GFR) is the gold standard measurement for assessing kidney function. It represents the volume of blood filtered by the glomeruli — the tiny filtering units in the kidneys — per unit of time, typically expressed in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73m²). A healthy adult typically has a GFR between 90 and 120 mL/min/1.73m², though this value naturally declines with age and varies by individual factors.

GFR is critically important because it serves as the primary indicator of overall kidney health and is used to stage chronic kidney disease (CKD). When the kidneys are damaged or functioning poorly, the GFR drops, indicating that the kidneys are not effectively filtering waste products, excess fluids, and electrolytes from the blood. Early detection of reduced GFR is essential because CKD often progresses silently without noticeable symptoms until it reaches advanced stages, at which point treatment options become significantly more limited.

This calculator estimates GFR using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, which is currently the most widely recommended formula by nephrology organizations worldwide, as well as the older MDRD (Modification of Diet in Renal Disease) study equation. The CKD-EPI equation was developed in 2009 and has been shown to be more accurate than the MDRD equation, particularly in individuals with higher GFR values and without kidney disease.

How to Use

Using the GFR Calculator is straightforward and requires only a few inputs:

Enter Your Age: Input your age in years. GFR naturally declines with age due to normal physiological changes in kidney structure and function. Age is a critical variable in all GFR estimation equations.
Enter Your Serum Creatinine Level: Input your most recent serum creatinine measurement in milligrams per deciliter (mg/dL). Creatinine is a waste product generated from muscle metabolism and is filtered by the kidneys. Higher creatinine levels generally indicate lower kidney function. For reference, normal serum creatinine ranges are approximately 0.7–1.3 mg/dL for adult males and 0.6–1.1 mg/dL for adult females.
Select Your Gender: Choose between Male or Female. Gender affects GFR estimation because average muscle mass and creatinine production differ between males and females. Males typically produce more creatinine due to greater muscle mass, which is why gender-specific coefficients are applied in the formulas.
Review Your Results: The calculator will display your estimated GFR value in mL/min/1.73m² along with the corresponding CKD stage classification. Higher values indicate better kidney function.

For the most accurate results, use a recent blood test result for serum creatinine. If your creatinine is reported in micromoles per liter (μmol/L), you can convert it to mg/dL by dividing by 88.4.

Example Calculation

A 55-year-old male with a serum creatinine of 1.2 mg/dL:

CKD-EPI estimate: approximately 72 mL/min/1.73m²
MDRD estimate: approximately 69 mL/min/1.73m²
Classification: Mild decrease (Stage 2 CKD)

A 65-year-old female with a serum creatinine of 1.5 mg/dL:

CKD-EPI estimate: approximately 42 mL/min/1.73m²
MDRD estimate: approximately 39 mL/min/1.73m²
Classification: Moderate decrease (Stage 3 CKD)

Formulas and Calculations

The GFR Calculator uses two established equations for estimating kidney function from serum creatinine levels.

CKD-EPI 2021 Equation (Combined)

The CKD-EPI equation was developed using data from multiple studies and provides more accurate GFR estimates than the MDRD equation across a wider range of GFR values and patient populations:

\text{GFR} = 142 \times \left(\frac{\text{Scr}}{\kappa}\right)^{\alpha} \times (0.9938)^{\text{Age}} \times [1.012 \text{ if female}]

Where:

Scr = serum creatinine in mg/dL
κ (kappa) = 0.9 for males, 0.7 for females
α (alpha) = -0.302 for males, -0.241 for females (when Scr ≤ κ); -1.200 for males, -1.209 for females (when Scr > κ)
Age = patient age in years
Gender factor: multiply by 1.012 if female

MDRD Study Equation (4-variable)

The Modification of Diet in Renal Disease (MDRD) equation was developed in the 1990s and was the standard GFR estimating equation before CKD-EPI. It remains widely used in clinical practice:

\text{GFR} = 175 \times (\text{Scr})^{-1.154} \times (\text{Age})^{-0.203} \times [0.742 \text{ if female}]

Where:

Scr = serum creatinine in mg/dL
Age = patient age in years
The result is automatically adjusted for body surface area (normalized to 1.73m²)

Interpretation of Variables

Serum Creatinine (Scr): A breakdown product of creatine phosphate in muscle. It is produced at a relatively constant rate and freely filtered by the glomerulus. Elevated levels indicate reduced filtration capacity.
Age: Kidney function naturally declines with age due to decreased nephron mass and reduced renal blood flow. On average, GFR declines by approximately 1 mL/min/1.73m² per year after age 40.
Gender Coefficient: The 0.742 multiplier for females accounts for lower average muscle mass and creatinine production compared to males.

Additionally, for patients where creatinine-based estimates may be unreliable, cystatin C provides an alternative filtration marker. The CKD-EPI cystatin C equation is: GFR = 133 × (Scys)^(-0.499) × (0.996)^Age × [0.932 if female], where Scys = serum cystatin C in mg/L. This equation may be more accurate in certain populations, including the elderly, obese individuals, and those with unusual muscle mass.

Reference Tables

CKD Classification by GFR Level

Stage	GFR (mL/min/1.73m²)	Description	Clinical Significance
G1	≥ 90	Normal or High	Kidney function is normal, but other signs of kidney damage may be present
G2	60–89	Mild Decrease	Slightly below normal; may indicate early kidney disease
G3a	45–59	Mild to Moderate	Moderate impairment; increased risk of complications
G3b	30–44	Moderate to Severe	Significant impairment; referral to nephrologist recommended
G4	15–29	Severe Decrease	Severe impairment; prepare for kidney replacement therapy
G5	< 15	Kidney Failure	End-stage renal disease; dialysis or transplant required

Serum Creatinine Reference Ranges

Population	Typical Range (mg/dL)	Notes
Adult Males	0.7–1.3	Higher due to greater muscle mass
Adult Females	0.6–1.1	Lower due to less muscle mass
Older Adults	0.6–1.2	May not rise despite declining GFR due to reduced muscle mass

GFR Thresholds and Clinical Actions

GFR Level	Recommended Actions
≥ 90 mL/min	Monitor annually if risk factors present
60–89 mL/min	Evaluate for kidney damage markers; monitor every 6–12 months
45–59 mL/min	Nephrology consultation; monitor every 6 months
30–44 mL/min	Nephrology referral; monitor every 3–6 months
15–29 mL/min	Prepare for kidney replacement therapy; monitor every 1–3 months
< 15 mL/min	Initiate dialysis evaluation or transplant workup

Limitations

Estimation, Not Measurement: This calculator provides an estimate of GFR based on mathematical equations, not a direct measurement. Measured GFR (mGFR) using techniques like inulin clearance or iothalamate clearance is more accurate but is complex, expensive, and not routinely performed in clinical settings.
Creatinine Limitations: The estimates rely on serum creatinine, which can be influenced by factors unrelated to kidney function. Individuals with high muscle mass (athletes, bodybuilders) may have elevated creatinine levels despite normal kidney function. Conversely, elderly individuals or those with low muscle mass (cachexia, amputation) may have deceptively low creatinine levels despite significant kidney impairment.
Dietary Effects: High-protein diets, creatine supplementation, and certain foods (cooked meat) can temporarily elevate serum creatinine, potentially underestimating GFR. Similarly, very low protein diets or severe liver disease may lower creatinine independent of kidney function.
Race and Ethnicity: Some GFR estimating equations historically included race-based coefficients, which has been controversial. The CKD-EPI 2021 equation has removed the race coefficient, but accuracy may still vary across different population groups.
Acute Kidney Injury: These equations are designed to estimate GFR in steady-state conditions and may not accurately reflect rapidly changing kidney function in acute kidney injury (AKI) settings.
Body Size and Composition: The equations normalize results to a standard body surface area of 1.73m², which may not accurately reflect kidney function in individuals who are significantly underweight, obese, or have unusual body composition.
Drugs and Substances: Certain medications (trimethoprim, cimetidine) can block creatinine secretion in the kidney tubules, artificially elevating serum creatinine and underestimating GFR.
Pregnancy: GFR naturally increases by approximately 50% during pregnancy. These equations have not been validated for use in pregnant women and should not be used for that population.

Practical Tips

Consult Your Doctor: Always discuss your GFR results with a healthcare professional. GFR is just one piece of the puzzle — actual kidney health assessment also considers urine tests, imaging, blood pressure, and clinical history. Your doctor may recommend additional testing such as urine albumin-to-creatinine ratio (ACR) or imaging studies.
Use Recent Lab Results: For the most accurate estimate, use your most recent serum creatinine measurement. Kidney function can change over time based on hydration, medications, and other factors. Creatinine levels can fluctuate day to day.
Consider Multiple Estimates: Some clinicians recommend using both the CKD-EPI and MDRD equations together, as well as cystatin C-based estimates, to get a more complete picture of kidney function. Discrepancies between estimates may warrant further investigation.
Track Trends: A single GFR number provides limited information. Tracking your GFR over time (along with urine albumin and other markers) is more informative for assessing disease progression. Regular monitoring allows early detection of worsening kidney function.
Know Your Numbers: Understanding your GFR helps you make informed decisions about your health, follow appropriate monitoring schedules, and communicate effectively with your healthcare provider. Keep a record of your GFR results over time.
Medication Adjustments: Many medications require dose adjustments based on kidney function. If your GFR is below 60 mL/min/1.73m², inform your healthcare provider so they can review your medications and make appropriate adjustments.

Frequently Asked Questions

What is a normal GFR?: A normal GFR is generally considered to be 90 mL/min/1.73m² or higher, though GFR naturally declines with age. For a healthy young adult, typical values range from 90–120 mL/min/1.73m².
Can GFR improve?: In some cases, yes. Certain causes of kidney function decline (such as dehydration, urinary tract obstruction, or medication effects) are reversible with appropriate treatment. However, in chronic kidney disease, GFR loss is typically progressive.
What is the difference between CKD-EPI and MDRD?: CKD-EPI is a newer equation generally considered more accurate, especially at higher GFR values. MDRD was the standard for many years but tends to underestimate GFR in people with near-normal kidney function. The CKD-EPI equation is now recommended by most nephrology guidelines.
Do I need to fast before the test?: No fasting is required for a serum creatinine test. However, you should avoid eating large amounts of cooked meat before the test, as it can temporarily increase creatinine levels.
At what GFR level do symptoms appear?: Most people with CKD stages 1–3 do not experience noticeable symptoms. Symptoms such as fatigue, swelling, changes in urination, and shortness of breath typically do not appear until stage 4 or 5, when kidney function is severely reduced.

References

Levey, A.S., et al. (2009). "A New Equation to Estimate Glomerular Filtration Rate." Annals of Internal Medicine, 150(9), 604–612.
Levey, A.S., et al. (1999). "A More Accurate Method to Estimate Glomerular Filtration Rate from Serum Creatinine: A New Prediction Equation." Annals of Internal Medicine, 130(6), 461–470.
National Kidney Foundation. (2002). "K/DOQI Clinical Practice Guidelines for Chronic Kidney Disease." American Journal of Kidney Diseases, 39(2), S1–S266.
Inker, L.A., et al. (2021). "New GFR and Albuminuria Equations for CKD." American Journal of Kidney Diseases, 77(6), 800–816.
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). (2023). "Your Kidneys & How They Work."
Stevens, L.A., et al. (2006). "Assessing Kidney Function — Measured and Estimated Glomerular Filtration Rate." New England Journal of Medicine, 354(23), 2473–2483.

Last updated: May 24, 2026