GFR Calculator - Estimated Glomerular Filtration Rate
Estimate kidney function (eGFR) from age, sex, and serum creatinine using the CKD-EPI 2021 race-free equation. Includes CKD stage classification.
🫘 What is Estimated Glomerular Filtration Rate (eGFR)?
Estimated glomerular filtration rate (eGFR) is a calculated measure of how well the kidneys are filtering waste from the blood, expressed in millilitres per minute per 1.73 square metres of body surface area (mL/min/1.73m²). Rather than measuring GFR directly, which requires a complex and expensive clinical procedure involving an injected filtration marker, eGFR is estimated from a routine blood test result (serum creatinine) combined with age and sex, using a validated statistical equation. It is the primary number doctors use to detect, stage, and monitor chronic kidney disease.
This calculator uses the CKD-EPI 2021 creatinine equation, published by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and now the standard equation recommended by the National Kidney Foundation and American Society of Nephrology. It is used in everyday clinical practice every time a doctor orders a "comprehensive metabolic panel" or "basic metabolic panel" blood test, since most labs now report an eGFR automatically alongside the raw serum creatinine value. It is also used before prescribing certain medications that are cleared by the kidneys and need dose adjustment when kidney function is reduced, and to decide when a patient should be referred to a kidney specialist (nephrologist).
A common misconception is that a single eGFR reading, by itself, diagnoses chronic kidney disease. In practice, a clinical CKD diagnosis requires either persistently reduced eGFR (typically below 60 for at least 3 months) or other evidence of kidney damage, such as protein in the urine, confirmed with repeat testing and full clinical context. Another common misconception is that all people with the same eGFR number have identical kidney health; the equation is a population-based estimate, and individual results can be affected by muscle mass, hydration, diet, and recent illness. A related and important change: the 2021 version of this equation removed an earlier race-based coefficient, so the same formula and coefficients now apply to every adult regardless of race.
This calculator computes eGFR from age, sex, and serum creatinine using the exact CKD-EPI 2021 race-free formula, and automatically classifies the result into the standard G1 through G5 chronic kidney disease stages used in clinical guidelines, so you can see both the number and what it typically means in context.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1: Male, Age 60, Normal Creatinine
Male, age 60, Scr = 1.0 mg/dL
Example 2: Female, Age 45, Low-Normal Creatinine
Female, age 45, Scr = 0.6 mg/dL
Example 3: Male, Age 70, Elevated Creatinine
Male, age 70, Scr = 2.5 mg/dL
❓ Frequently Asked Questions
🔗 Related Calculators
What is eGFR and why does it matter?
Estimated glomerular filtration rate (eGFR) approximates how many millilitres of blood the kidneys filter per minute, normalised to a standard body size (mL/min/1.73m²). It is the single most widely used measure of overall kidney function, used to detect, stage, and monitor chronic kidney disease (CKD) and to guide dosing of many medications that are cleared by the kidneys.
What is the CKD-EPI 2021 equation?
The CKD-EPI 2021 creatinine equation is eGFR = 142 × (Scr/k)^α × 0.9938^Age × (1.012 if female), where Scr is serum creatinine in mg/dL, k is 0.7 for females and 0.9 for males, and α depends on whether Scr is below or above k. It was published by the CKD-EPI collaboration in 2021 specifically to remove the previous race coefficient, so the same equation now applies to all adults.
Why was the race coefficient removed from the GFR equation?
Earlier CKD-EPI and MDRD equations included a coefficient that assigned a higher eGFR to patients coded as Black, based on population-level average creatinine differences. Medical organisations including the National Kidney Foundation and American Society of Nephrology concluded that using race as a proxy in an individual clinical calculation was scientifically unsound and could delay diagnosis or specialist referral for some patients, so the 2021 equation uses only age, sex, and serum creatinine.
What are the CKD stages based on eGFR?
Stage G1 is eGFR 90 or above (normal or high function, but only a CKD stage if kidney damage markers are also present). G2 is 60-89 (mildly decreased). G3a is 45-59 and G3b is 30-44 (moderately decreased). G4 is 15-29 (severely decreased). G5 is below 15 (kidney failure, often requiring dialysis or transplant). All ranges are in mL/min/1.73m².
What is a normal eGFR value?
A normal eGFR for a healthy young adult is typically 90 mL/min/1.73m² or higher. eGFR naturally declines with age; a healthy 70-year-old may have an eGFR in the 60s or 70s without any kidney disease. A single eGFR below 60 for 3 or more months is generally required to diagnose chronic kidney disease, alongside other clinical findings.
How does serum creatinine relate to eGFR?
Serum creatinine (Scr) is a waste product from muscle metabolism that healthy kidneys filter out efficiently. As kidney function declines, creatinine builds up in the blood, so a higher Scr corresponds to a lower estimated eGFR. Because creatinine is also affected by muscle mass, age, and sex, the CKD-EPI equation adjusts for these factors rather than using raw creatinine alone.
Why does eGFR decrease with age even in healthy people?
The CKD-EPI equation includes a term, 0.9938 raised to the power of age, that reduces the estimated eGFR slightly for every additional year of age. This reflects the well-documented average decline in kidney filtering capacity that occurs even in people without kidney disease, roughly a few mL/min/1.73m² lost per decade after young adulthood.
Why do male and female use different constants in the equation?
Average serum creatinine differs between men and women partly because of differences in average muscle mass, since creatinine is a byproduct of muscle metabolism. The equation uses k = 0.9 mg/dL for males and k = 0.7 mg/dL for females as reference creatinine values, plus a 1.012 multiplier for females, to produce comparable eGFR estimates across sexes at a given true kidney function level.
Can this calculator diagnose chronic kidney disease?
No. This calculator estimates eGFR from a single set of inputs for educational purposes only. A clinical CKD diagnosis requires a doctor to confirm reduced eGFR or other markers of kidney damage (such as protein in the urine) persisting for at least 3 months, alongside your full medical history. Always have blood and urine test results interpreted by a qualified physician or nephrologist.
What factors can make this eGFR estimate inaccurate?
Serum creatinine, and therefore any eGFR estimated from it, can be affected by very high or low muscle mass (bodybuilders, amputees, or people with muscle-wasting conditions), a recent high-protein meal, dehydration, certain medications, pregnancy, and acute illness. In these situations a doctor may use an alternative marker such as cystatin C, or a direct measured GFR test, for a more accurate result.
What should I do if my eGFR result falls in a low stage?
Do not self-diagnose or change any medication based on this calculator. Share the result with your doctor, who can confirm it with repeat testing, check for protein in your urine, review your medication list for kidney-affecting drugs, and refer you to a nephrologist if needed. Many causes of reduced eGFR, such as dehydration or a temporary medication effect, are reversible if caught early.