Your glomerular filtration rate (GFR) tells you how well your kidneys filter waste from your blood. Enter your serum creatinine level, age, and sex into the calculator above to get an estimated GFR (eGFR) in seconds.
This eGFR calculator uses the recommended 2021 CKD-EPI equations to estimate glomerular filtration rate for adults 18 and older. It also supports the MDRD GFR equation and a pediatric option for children. Use the result as a screening estimate, not a diagnosis. Always confirm findings with your doctor.
How the eGFR Calculator Works to Estimate GFR
The calculator takes a few lab values and personal details, then applies a validated formula to estimate how many milliliters of blood your kidneys clean per minute.
Here is what you need to enter:
- Serum creatinine (mg/dL or µmol/L). This comes from a standard blood test.
- Age in years.
- Sex assigned at birth. The 2021 CKD-EPI equation uses sex as a biological variable in the formula.
- Cystatin C (mg/L), if available. Adding this protein marker can improve accuracy.
Once you click calculate, the tool plugs your inputs into the selected equation. The result is your eGFR, expressed in mL/min/1.73 m², which is normalized to body surface area. A higher number means better kidney function.
The eGFR is calculated using standardized creatinine values. If your lab does not use an assay traceable to the international reference method, the estimate may be less reliable.
Glomerular Filtration Rate and Why It Matters for Kidney Health
GFR stands for glomerular filtration rate. It measures the volume of blood your kidneys filter through tiny structures called glomeruli each minute. Think of it as a speedometer for kidney function.
Healthy kidneys clean your blood efficiently, removing waste products like creatinine and urea while keeping useful proteins in circulation. When GFR drops, waste builds up. Over time, a sustained low GFR signals chronic kidney disease (CKD).
Knowing your estimated GFR helps you and your doctor:
- Detect early loss of kidney function before symptoms appear
- Determine which stage of chronic kidney disease applies
- Decide whether to adjust medications cleared by the kidneys
- Track whether treatment is helping slow the progression of CKD
GFR is considered the best single measure of kidney function by the National Kidney Foundation and the American Society of Nephrology. A single blood test for serum creatinine is usually enough to estimate it.
Normal GFR Levels by Age and CKD Stage
A normal GFR for a healthy young adult is roughly 90 to 120 mL/min/1.73 m². GFR naturally declines with age, so a reading of 70 in a 75-year-old may not indicate disease on its own.
Here is a general reference for normal GFR levels by age range:
| Age range | Typical average GFR (mL/min/1.73 m²) |
|---|---|
| 20–29 | 116 |
| 30–39 | 107 |
| 40–49 | 99 |
| 50–59 | 93 |
| 60–69 | 85 |
| 70+ | 75 |
These are population averages. Individual results vary based on muscle mass, diet, hydration, and other factors.
CKD stages map directly to GFR levels:
| CKD Stage | GFR range (mL/min/1.73 m²) | Description |
|---|---|---|
| 1 | 90 or above | Normal or high GFR with evidence of kidney damage |
| 2 | 60–89 | Mildly decreased GFR with evidence of kidney damage |
| 3a | 45–59 | Mild to moderate decrease |
| 3b | 30–44 | Moderate to severe decrease |
| 4 | 15–29 | Severe decrease |
| 5 | Below 15 | Kidney failure |
Stage 1 CKD requires both a GFR of 90 or above and separate evidence of kidney damage, such as albuminuria or imaging findings. GFR alone does not confirm CKD at that level.
2021 CKD-EPI Equations for Adult eGFR Calculator
In 2021, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) updated its equations to estimate GFR without using a race variable. This change, endorsed by the National Kidney Foundation and the American Society of Nephrology, applies to all adults 18 and older.
The 2021 CKD-EPI equations are now the recommended standard for clinical labs and calculators in the United States.
CKD-EPI Creatinine Equation
The CKD-EPI creatinine equation uses serum creatinine, age, and sex. It is the most widely available option because creatinine is included in routine metabolic panels.
The formula adjusts coefficients based on sex and whether the amount of creatinine falls above or below a sex-specific threshold (0.7 mg/dL for females, 0.9 mg/dL for males). The equation assumes a standardized creatinine assay traceable to isotope dilution mass spectrometry (IDMS).
This version works well for most adults. Accuracy drops in people with very high or very low muscle mass, because creatinine production depends partly on muscle.
CKD-EPI Cystatin C Equation
Cystatin C is a small protein produced by nearly all cells. Unlike creatinine, its blood level is not strongly influenced by muscle mass or diet.
The CKD-EPI cystatin C equation uses cystatin C, age, and sex. Some clinicians prefer it for patients where creatinine-based estimates may be unreliable:
- People with amputations or muscle-wasting conditions
- Those on very high or very low protein diets
- Patients with decreased GFR who need a confirmatory estimate
A combined creatinine-cystatin C equation also exists and is generally the most accurate of the three. If your lab provides both markers, the calculator can use the combined formula for a more precise eGFR value.
MDRD GFR Equation and When to Use It
The Modification of Diet in Renal Disease (MDRD) equation was developed from the Diet in Renal Disease Study (Levey et al.). For years it was the primary formula used to estimate GFR in clinical practice.
The MDRD equation uses four variables: serum creatinine, age, sex, and (in the original version) race. It performs best when GFR is below 60 mL/min/1.73 m².
Key limitations of the MDRD GFR equation:
- It tends to underestimate GFR in people with near-normal kidney function (GFR above 60).
- It was developed in a population with known renal disease, so it is less validated for general screening.
- Older versions used a race coefficient that has since been removed from updated recommendations.
The 2021 CKD-EPI equations have largely replaced the MDRD equation for routine clinical use. However, some labs still report MDRD-based results, and the calculator here includes it for reference.
If your most recent available eGFR was calculated using the MDRD equation, you can compare it to a CKD-EPI result by running both in this tool.
Pediatric GFR Calculator: Estimating Kidney Function in Children
GFR in children cannot be estimated with adult equations. Body size, muscle mass, and creatinine production change rapidly during growth.
The most common formula for pediatric GFR estimation is the Schwartz equation (sometimes called the "bedside Schwartz"), which uses:
- Serum creatinine (standardized assay)
- Height in centimeters
The revised bedside Schwartz formula is:
eGFR = 0.413 × (height in cm / serum creatinine in mg/dL)
This equation is validated for use in children aged 1 to 17. For infants under one year, different reference ranges and methods apply. Always work with a pediatric nephrologist for interpretation.
Normal GFR in children reaches adult-level values (around 90 to 120 mL/min/1.73 m²) by approximately age 2. Values below 60 sustained over three months meet criteria for CKD in children, just as in adults.
eGFR Calculator for Adults vs. Pediatric GFR Calculator
The adult eGFR calculator and the pediatric GFR calculator serve the same purpose but use different equations and inputs.
| Feature | Adult eGFR calculator | Pediatric GFR calculator |
|---|---|---|
| Age range | 18 and older | 1–17 |
| Primary equation | 2021 CKD-EPI (creatinine or cystatin C) | Bedside Schwartz |
| Inputs | Creatinine, age, sex (± cystatin C) | Creatinine, height |
| Race variable | Removed in 2021 update | Not used |
Do not use the adult equations for children, and do not use the Schwartz equation for adults. Applying the wrong formula will produce misleading GFR estimates.
If a teenager is close to 18, some clinicians compare both results. The calculator flags which equation was applied so there is no confusion.
What Your eGFR Estimate Means for Chronic Kidney Disease
An eGFR value gives you a snapshot. A single reading is not a diagnosis. CKD is defined as abnormal kidney structure or function present for more than three months.
GFR Levels and CKD Stages
To classify CKD, clinicians look at two things together:
- eGFR value. Determines the stage (see the table above).
- Evidence of kidney damage. This includes albuminuria (protein in urine), abnormal urine sediment, imaging abnormalities, a history of kidney transplant, or biopsy findings.
A GFR below 60 for three or more months qualifies as CKD even without other markers. A GFR above 60 only counts as CKD if there is separate evidence of kidney damage, such as persistent albuminuria.
Staging matters because it guides treatment. Patients with chronic kidney disease at stage 3b or below may need dietary changes, blood pressure targets, and closer lab monitoring to slow the progression of CKD.
When to See a Nephrologist
Consider asking your doctor for a referral to nephrology if:
- Your eGFR is below 30 (CKD stage 4 or 5)
- Your eGFR is dropping rapidly (more than 5 mL/min/1.73 m² per year)
- You have persistent albuminuria with an albumin-to-creatinine ratio above 300 mg/g
- The cause of kidney function decline is unclear
- You have CKD complicated by difficult-to-control hypertension or anemia
Early referral to a kidney doctor can improve outcomes. Patients referred to nephrology before reaching stage 5 have better preparation for dialysis or kidney transplant if needed.
Serum Creatinine, Albuminuria, and Other Inputs the GFR Calculator Uses
Understanding each input helps you interpret results.
Serum creatinine is a waste product from normal muscle metabolism. Your kidneys filter it out. When kidney function drops, the amount of creatinine in your blood rises. Labs measure it using standardized creatinine assays calibrated to international reference materials.
Cystatin C is an alternative filtration marker. It is less affected by muscle mass, diet, or exercise than creatinine. Not every routine blood test includes it, so you may need to request it.
Age matters because GFR naturally declines over time. The equations account for this.
Sex influences creatinine production. Males typically have higher muscle mass and higher baseline creatinine levels.
Albuminuria is not an input to the GFR equation itself, but it is essential for CKD classification. Your doctor measures it with a urine test. Persistent albuminuria (albumin-to-creatinine ratio above 30 mg/g on two or more samples) is a key marker of kidney damage.
Height is required only for the pediatric GFR calculator (Schwartz equation).
Limitations of Using a Calculator to Estimate Glomerular Filtration Rate
Every GFR estimate has boundaries. Keep these in mind:
- It is an estimate, not a measurement. True GFR requires an inulin clearance test or similar procedure. Equations estimate GFR using surrogate markers.
- Muscle mass extremes reduce accuracy. Bodybuilders, amputees, and people with severe malnutrition may get misleading creatinine-based results. Cystatin C equations can help in these cases.
- Acute changes are not captured. These equations assume stable kidney function. In acute renal failure, creatinine levels change rapidly and the eGFR calculation lags behind actual function.
- Diet and supplements matter. High-protein meals or creatine supplements can temporarily raise serum creatinine, lowering the eGFR value artificially.
- Certain medications interfere. Some drugs (like trimethoprim or cimetidine) block creatinine secretion in the kidney tubules, raising blood creatinine without a real change in GFR.
- The equation was developed in specific populations. The 2021 CKD-EPI equations were validated primarily in U.S. and European cohorts. Accuracy may vary in other populations.
No online calculator replaces clinical judgment. Use your eGFR as a planning tool and discuss results with your healthcare provider.
GFR Calculator, eGFR Calculator, and MDRD GFR: Common Questions
Is the 2021 CKD-EPI the Same as the MDRD GFR Equation?
No. The 2021 CKD-EPI and the MDRD equation are different formulas developed by different research groups.
The MDRD equation (Levey et al.) came from the Modification of Diet in Renal Disease Study. It works best when GFR is below 60 but tends to underestimate higher values.
The 2021 CKD-EPI equations (Inker, Eneanya, Coresh J, et al., published in Ann Intern Med and the New England Journal of Medicine) were developed across more diverse populations and removed the race variable. They are more accurate across a wider GFR range and are now the recommended standard.
Can This GFR Calculator Replace a Kidney Function Blood Test?
No. The calculator requires lab results as inputs. You still need a blood test to measure serum creatinine or cystatin C.
The calculator automates the math so you do not have to compute the equation by hand. It is a convenience tool, not a substitute for laboratory evaluation.
What Is a Normal GFR for Someone with Diabetes or Hypertension?
The same GFR thresholds apply regardless of whether you have diabetes and hypertension. A GFR above 90 is considered normal, and below 60 suggests moderate kidney impairment.
However, people with diabetes or hypertension face a higher risk of kidney damage even when GFR is still normal. That is why guidelines recommend regular screening with both eGFR and urine albumin testing for these patients. Catching early changes lets you and your doctor act sooner to protect kidney health.
How Often Should I Estimate GFR If I Have CKD Risk Factors?
If you have risk factors for CKD (diabetes, hypertension, family history of kidney disease, or age over 60), most guidelines recommend checking eGFR at least once a year.
If you already have a diagnosis of CKD, your doctor may order labs more frequently. Patients with CKD stage 3 or higher often have creatinine and eGFR checked every 3 to 6 months. The goal is to track trends over time, since a single eGFR value is less informative than a pattern of results.