GFR Calculator — Estimate Kidney Function (CKD-EPI 2021)
This eGFR calculator uses the CKD-EPI 2021 race-free equation to estimate your Glomerular Filtration Rate from serum creatinine, age, and biological sex. Enter your values to see your eGFR in mL/min/1.73 m² and your CKD stage (G1–G5). A normal eGFR is 90 or above; values below 60 for more than 3 months may indicate Chronic Kidney Disease.
Medical Disclaimer
This tool is for informational purposes only. eGFR is an estimate, not a diagnosis. CKD requires at least two measurements separated by 3 months, plus clinical evaluation. Consult your healthcare provider for medical advice.
Glomerular Filtration Rate (eGFR) Calculator
Enter your serum creatinine, age, and sex to estimate your GFR using the CKD-EPI 2021 (race-free) equation.
Normal range: 0.6–1.2 mg/dL (male), 0.5–1.1 mg/dL (female)
The CKD-EPI 2021 equation uses biological sex for accuracy. Select the sex assigned at birth or as determined by your lab.
Frequently Asked Questions
What is eGFR and why does it matter?
eGFR (estimated Glomerular Filtration Rate) measures how well your kidneys filter waste from your blood, expressed in mL/min/1.73 m². A normal eGFR is above 90. Lower values indicate reduced kidney function and may signal Chronic Kidney Disease (CKD). eGFR is the primary test used to detect and stage CKD.
What is the CKD-EPI 2021 equation?
The CKD-EPI 2021 equation is the current gold-standard formula for estimating GFR from serum creatinine, age, and sex. Published by Inker et al. in the New England Journal of Medicine (2021), it removed the race coefficient used in the earlier 2009 version to improve equity and accuracy across diverse populations.
What is a normal GFR level?
A normal eGFR for a healthy adult is 90 mL/min/1.73 m² or higher (CKD Stage G1). eGFR naturally declines with age — values of 60–89 (Stage G2) may be normal in older adults without other signs of kidney damage. An eGFR consistently below 60 for more than 3 months indicates Chronic Kidney Disease.
What are the CKD stages based on GFR?
CKD is staged G1 through G5: G1 (eGFR ≥90, normal or high), G2 (60–89, mildly decreased), G3a (45–59, mildly to moderately decreased), G3b (30–44, moderately to severely decreased), G4 (15–29, severely decreased), G5 (<15, kidney failure). Stages G3b and above warrant nephrology referral.
What serum creatinine level is dangerous?
There is no single dangerous creatinine level — context matters. For most adult males, creatinine above 1.2 mg/dL, and for females above 1.1 mg/dL, may indicate reduced kidney function. A creatinine of 2.0 mg/dL typically corresponds to roughly 50% reduction in kidney function. Values above 4–5 mg/dL usually indicate severely impaired kidney function requiring urgent medical attention.
How does age affect GFR?
GFR naturally declines with age, typically by about 1 mL/min/year after age 40. A 70-year-old with an eGFR of 65 may have age-related decline rather than disease. However, any eGFR below 60 — regardless of age — requires evaluation for CKD, especially if accompanied by proteinuria or other markers of kidney damage.
Why does sex affect the GFR calculation?
The CKD-EPI 2021 equation uses biological sex because creatinine production correlates with muscle mass, which differs on average between males and females. Females have a lower creatinine threshold (kappa = 0.7 vs 0.9) and a 1.2% sex multiplier that accounts for systematic differences in creatinine excretion.
What symptoms are associated with low GFR?
Early CKD (G1–G3) often has no symptoms. Advanced CKD (G4–G5) may cause fatigue, swollen ankles/feet, shortness of breath, nausea, foamy urine (proteinuria), decreased urine output, and high blood pressure. If you have these symptoms along with a low eGFR, seek medical evaluation promptly.
How to Calculate eGFR (CKD-EPI 2021 Equation)
What is eGFR?
The estimated Glomerular Filtration Rate (eGFR) measures how well your kidneys filter waste and excess fluids from your blood. It is expressed in milliliters per minute per 1.73 m² of body surface area (mL/min/1.73 m²).
A higher eGFR indicates better kidney function. Normal eGFR for a healthy young adult is typically above 90 mL/min/1.73 m². eGFR naturally declines with age — a value slightly below 60 in an older adult may require further evaluation but does not always indicate kidney disease.
eGFR is calculated from serum creatinine — a waste product of muscle metabolism that the kidneys filter out. When kidneys are impaired, creatinine accumulates in the blood, causing eGFR to fall.
CKD-EPI 2021 Equation
This calculator uses the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2021 creatinine equation, which is the current standard recommended by KDIGO (Kidney Disease: Improving Global Outcomes) guidelines. The 2021 revision removed the race coefficient present in the earlier 2009 equation.
eGFR = 142 × min(Scr/κ, 1)α × max(Scr/κ, 1)−1.200 × 0.9938&sup(Age) × Sex
Scr = Serum creatinine (mg/dL)
κ = 0.7 (female) or 0.9 (male)
α = −0.241 (female) or −0.302 (male)
Sex multiplier = 1.012 (female) or 1.000 (male)
Source: Inker LA, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. N Engl J Med.2021;385(19):1737–1749.
CKD Stages (G1–G5)
Chronic Kidney Disease (CKD) is classified into five stages based on eGFR. These stages guide clinical management and monitoring frequency.
| Stage | eGFR (mL/min/1.73 m²) | Description | Management |
|---|---|---|---|
| G1 | ≥ 90 | Normal or high | Monitor annually if risk factors present |
| G2 | 60–89 | Mildly decreased | Monitor annually; address risk factors |
| G3a | 45–59 | Mildly to moderately decreased | Monitor every 6 months |
| G3b | 30–44 | Moderately to severely decreased | Nephrology referral recommended |
| G4 | 15–29 | Severely decreased | Prepare for kidney replacement therapy |
| G5 | < 15 | Kidney failure | Dialysis or transplant evaluation |
CKD diagnosis requires eGFR below 60 mL/min/1.73 m² OR evidence of kidney damage (e.g., proteinuria, abnormal imaging) persisting for ≥ 3 months.
Creatinine Reference Ranges
Serum creatinine is the primary input for eGFR calculation. Normal ranges vary by sex, age, and muscle mass.
| Group | Normal Range (mg/dL) | Notes |
|---|---|---|
| Adult male | 0.7–1.2 | Higher due to greater muscle mass |
| Adult female | 0.5–1.1 | Lower average muscle mass |
| Elderly (>65) | May be lower | Less muscle; “normal” Scr may mask reduced GFR |
| Athletes | May be higher | High muscle mass increases creatinine production |
Tip:A single creatinine measurement can appear “normal” even in early kidney disease. Trending creatinine over time — and looking at the rate of change — is more informative than a one-time value.
When to See a Doctor
An eGFR result below certain thresholds — or a rapid decline — warrants medical evaluation:
- eGFR below 60 (Stage G3a or lower): Suggests possible CKD. Requires repeat testing, urine albumin measurement, and evaluation of underlying causes.
- eGFR below 30 (Stage G4): Nephrology referral is strongly recommended to plan for kidney replacement therapy if needed.
- eGFR below 15 (Stage G5): Urgent evaluation for dialysis or kidney transplant.
- Rapid decline (>5 mL/min/year): Even within “normal” ranges, rapid loss of kidney function requires investigation.
- Symptoms of kidney disease: Swelling in legs/ankles, foamy urine, persistent fatigue, or high blood pressure alongside low eGFR.
People with diabetes, hypertension, cardiovascular disease, or a family history of kidney disease should have eGFR checked regularly — at minimum annually.
Medical Disclaimer
This calculator is for informational purposes only and does not constitute medical advice.
- eGFR is an estimate, not a direct measurement of kidney filtration.
- The CKD-EPI 2021 equation is validated for adults; it should not be used for children.
- Results can be affected by diet, medications, hydration status, and muscle mass.
- A single eGFR value is not sufficient to diagnose CKD — repeat testing over 3 months is required.
- Always consult a qualified healthcare professional for interpretation and clinical decisions.
Sources: KDIGO 2012 Clinical Practice Guideline for CKD, NKF/ASN Task Force 2021 (Inker et al., N Engl J Med 2021).
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