eGFR Kidney Function Calculator

Overview: What This eGFR Calculator Does

This calculator estimates your estimated glomerular filtration rate (eGFR), a common measure of how well your kidneys filter waste products from the blood. It uses the 2009 CKD-EPI creatinine equation, which incorporates your age, serum creatinine level, sex assigned at birth, and whether you identify as Black.

The result is expressed in milliliters per minute per 1.73 square meters (mL/min/1.73 m²), which is a standard way of comparing kidney function across people of different body sizes. This tool is intended for adult users and for educational purposes only. It cannot diagnose disease or replace professional medical advice, testing, or treatment.

If your result is outside the range you expect, or if you have symptoms or risk factors for kidney disease (such as diabetes, high blood pressure, or a family history of kidney problems), discuss your numbers with a qualified health professional.

What Is eGFR and Why It Matters

Your kidneys continuously filter your blood, removing waste products, drugs, and excess fluid. The glomerular filtration rate (GFR) is the amount of blood filtered per minute by tiny filtering units in the kidneys called glomeruli. Because directly measuring GFR is complex and invasive, laboratories usually report an estimated GFR (eGFR) based on blood tests.

eGFR helps clinicians:

• Screen for chronic kidney disease (CKD) in people with risk factors.
• Stage the severity of CKD when present.
• Monitor changes in kidney function over time.
• Adjust medication doses that are cleared by the kidneys.

A persistently reduced eGFR (typically below 60 mL/min/1.73 m² for at least three months) is one of the criteria used to define chronic kidney disease. However, a single low result, especially from an online calculator, is not enough to make a diagnosis.

How the CKD-EPI Equation Works

This calculator uses the 2009 CKD-EPI creatinine-based equation, which was developed to give more accurate estimates of kidney function, especially when true GFR is above 60 mL/min/1.73 m². It relies on a blood test called serum creatinine, a waste product generated by muscle metabolism and cleared by the kidneys.

The CKD-EPI formula adjusts for differences in creatinine production and clearance associated with sex, age, and race. In simplified mathematical form, it can be written as:

Where:

• Scr = serum creatinine in milligrams per deciliter (mg/dL).
• κ (kappa) = 0.7 for females and 0.9 for males.
• α (alpha) = −0.329 for females and −0.411 for males.
• Age = age in years.
• Adj (adjustment factor) = 1.018 for females and 1.159 for individuals who identify as Black. If both apply, the factors are multiplied.

The min and max functions in the equation handle how creatinine values above or below a threshold affect the final estimate. The result is normalized to a body surface area of 1.73 m², a historical “average” adult size used in kidney research.

This equation was validated in large research cohorts, but like any model, it provides an estimate, not a direct measurement of true GFR.

How to Use the Calculator

To use this tool:

1. Enter your age in years. The calculator is designed for adults (typically 18 years and older).
2. Enter your most recent serum creatinine in mg/dL, as reported by your laboratory. Many adults have values that fall roughly between 0.6 and 1.3 mg/dL, but normal ranges vary.
3. Select your sex assigned at birth, because this affects typical muscle mass and creatinine generation.
4. Indicate whether you identify as Black, reflecting how the original CKD-EPI study modeled average creatinine production among different groups.
5. Submit the form to see your estimated GFR in mL/min/1.73 m².

For the most meaningful comparison, try to use values from the same laboratory over time, because testing methods and reference ranges can differ.

Interpreting Your eGFR Result

Healthy kidney function depends on many factors, including age. eGFR tends to decline gradually with aging, even in people without kidney disease. The table below summarizes commonly used eGFR ranges and how they are often described in clinical practice. These stages are usually applied only when reduced values are persistent and interpreted together with urine tests, imaging, and medical history.

*Stage labels are simplified and for general education. Only a clinician can formally diagnose chronic kidney disease.

Points to keep in mind when viewing your result:

• One value is not a trend. A single low or high eGFR should not be used alone to make decisions. Repeated testing over time is usually required.
• Age matters. An eGFR of 65 may be acceptable for an older adult but more concerning in a younger person.
• Context is crucial. The same eGFR value may have different implications depending on blood pressure, diabetes status, urine findings, and imaging results.
• Talk to your clinician. If your eGFR is below about 60 mL/min/1.73 m² or you have other risk factors, review the result with a healthcare professional.

Worked Example

The following example shows how the CKD-EPI equation might be applied in practice. Your calculator result will be computed automatically; you do not need to perform these steps yourself.

Example person:

• Age: 55 years
• Sex assigned at birth: Female
• Race: Not Black
• Serum creatinine: 1.1 mg/dL

Stepwise application:

1. Set κ = 0.7 and α = −0.329 (for females).
2. Compute Scr/κ = 1.1 / 0.7 ≈ 1.57.
3. Determine min(Scr/κ, 1) = min(1.57, 1) = 1.
4. Determine max(Scr/κ, 1) = max(1.57, 1) = 1.57.
5. Calculate the creatinine terms:
   • [min(Scr/κ, 1)]^α = 1^−0.329 = 1.
   • [max(Scr/κ, 1)]^−1.209 ≈ 1.57^−1.209 (a value < 1 that lowers the eGFR).
6. Calculate the age term: 0.993^Age = 0.993⁵⁵, which is also less than 1 and slightly reduces the estimate.
7. Apply adjustment factors: 1.018 for female and 1.0 for not Black, so overall Adj ≈ 1.018.

When all the steps are combined numerically, the eGFR might be, for example, around 58–60 mL/min/1.73 m² (exact value depends on rounding). This would often fall into the mildly to moderately decreased range and would usually prompt discussion with a clinician, especially if persistent on repeat testing.

Your own result may differ even with similar inputs because of differences in lab methods, rounding, or use of updated equations.

Limitations and Assumptions of This Calculator

While eGFR is widely used and very helpful, it has important limitations:

• Creatinine depends on muscle mass. People with very low muscle mass (for example, frail older adults, some people with chronic illness, or those with amputations) may have deceptively low creatinine and a falsely high eGFR. Very muscular individuals may have higher creatinine and a falsely low eGFR.
• Diet and medications can affect creatinine. High meat intake, some supplements, and certain drugs can change creatinine levels independently of kidney function.
• Acute illness is different from chronic disease. Dehydration, infections, or sudden loss of blood flow to the kidneys can cause temporary changes in creatinine and eGFR. Chronic kidney disease is defined by persistent abnormalities over at least three months.
• Adults only. The CKD-EPI equation is not validated for children. Pediatric kidney function is usually assessed with different formulas.
• Population-based equation. The formula was derived from large groups of people; individual results can vary.

Race Adjustment and Evolving Practice

This calculator uses the original 2009 CKD-EPI creatinine-based equation, which includes a race coefficient for individuals who identify as Black. The original research observed that, on average, Black participants had higher creatinine levels at the same measured GFR, likely reflecting differences in average muscle mass or other factors. This led to an adjustment that increases eGFR estimates for Black individuals.

However, many institutions and professional societies have raised concerns about the use of race in medical algorithms. As a result:

• Some laboratories have moved to race-free CKD-EPI equations.
• Others may use equations that combine creatinine with another blood marker called cystatin C.
• Different calculators and labs may therefore give different eGFR values for the same person.

When comparing your calculator result to a value from your lab report, confirm which equation and which units were used. Always rely on the interpretation provided by your healthcare team.

Assumptions Behind the Equation

The CKD-EPI formula assumes:

• Your creatinine level is stable (not rapidly rising or falling).
• Your laboratory uses a standardized creatinine assay that is calibrated similarly to the methods used in the research studies.
• Your body composition falls reasonably within the ranges seen in the original study populations.

If these assumptions are not met (for example, in severe liver disease, during pregnancy, or with very unusual body size), the eGFR may be less accurate. In such situations, clinicians may rely more heavily on other tests or direct measurements.

Maintaining Kidney Health

Protecting your kidneys can reduce the risk of chronic kidney disease or slow its progression. General strategies often recommended by clinicians include:

• Manage blood pressure. Keeping blood pressure within a target range is one of the most important ways to protect kidney function.
• Control blood sugar. For people with diabetes, good glucose control can substantially reduce the risk of kidney damage.
• Use pain relievers cautiously. Frequent or high-dose use of some over-the-counter pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs), may harm the kidneys, especially in people with existing kidney problems.
• Avoid smoking and tobacco. Smoking can worsen blood vessel damage, including in the kidneys.
• Stay hydrated. For most people, drinking enough fluids to avoid thirst and dark urine supports overall kidney health, unless a clinician has advised fluid restriction.
• Review medications regularly. Some prescription or herbal products can affect the kidneys. Check with your clinician or pharmacist, especially if you already have reduced kidney function.
• Schedule routine checkups. People with diabetes, high blood pressure, heart disease, or a family history of kidney failure may benefit from periodic blood and urine tests.

Any changes to medications, diet, or lifestyle should be discussed with a healthcare professional who knows your full medical history.

Important Safety Notes

• This calculator is for informational and educational purposes only.
• It is intended for adults and is not validated for children or pregnant individuals.
• Do not start, stop, or change medications based solely on an eGFR you calculate here.
• If your result is significantly lower than expected, if you have symptoms such as swelling, fatigue, shortness of breath, or changes in urination, or if you have known kidney disease, seek personalized advice from a qualified clinician.

Your healthcare provider can explain how your eGFR fits with other test results and what, if anything, you should do next.