eGFR Calculator – Estimated Glomerular Filtration Rate
Free eGFR calculator using the 2021 CKD-EPI formula. Estimate kidney function from serum creatinine, age, and sex. Check your CKD stage and understand your results.
What Is eGFR and Why Is It Important?
eGFR — Estimated Glomerular Filtration Rate — is the best measure of kidney function available through a routine blood test. It estimates how much blood your kidneys filter per minute per 1.73 m² of body surface area. Healthy kidneys filter approximately 90–120 mL of blood per minute. As kidney disease progresses, this rate falls.
The "glomeruli" are the tiny filtering units inside each kidney — you have approximately 1 million of them per kidney. When the glomeruli are damaged (by diabetes, high blood pressure, infection, medications, or other conditions), the filtration rate drops, and waste products accumulate in the blood.
Why this matters:
- An estimated 850 million people worldwide have chronic kidney disease (CKD)
- Most people have NO symptoms until CKD is in stage 3 or later (eGFR below 60)
- eGFR is the primary marker for CKD staging, treatment decisions, and medication dosing
- Many medications (metformin, NSAIDs, certain antibiotics) are contraindicated or dose-adjusted below specific eGFR thresholds
- Kidney disease is the 10th leading cause of death globally and a major driver of cardiovascular risk
eGFR is calculated from a routine blood test for serum creatinine — a waste product of muscle metabolism that the kidneys filter out. When kidneys aren't working well, creatinine builds up in the blood, and eGFR (calculated from this level) falls.
eGFR Formula: The 2021 CKD-EPI Equation
This calculator uses the 2021 CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation — the current gold standard, updated in 2021 to remove the race coefficient (which was previously a factor for Black patients).
The 2021 CKD-EPI formula (in mg/dL):
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(−1.200) × 0.9938^Age × 1.012 [if female]
Where:
- Scr = serum creatinine in mg/dL
- κ = 0.7 for females, 0.9 for males
- α = −0.241 for females, −0.302 for males
- min() = the minimum of Scr/κ or 1
- max() = the maximum of Scr/κ or 1
- The 1.012 multiplier applies only to females
Example (male, age 55, creatinine 1.2 mg/dL):
- κ = 0.9, α = −0.302
- Scr/κ = 1.2/0.9 = 1.333 → min = 1, max = 1.333
- eGFR = 142 × 1^(−0.302) × 1.333^(−1.200) × 0.9938^55
- = 142 × 1 × 0.756 × 0.713 = 76.5 mL/min/1.73m²
To convert creatinine from µmol/L to mg/dL: divide by 88.4.
Why the 2021 update? The previous 2009 CKD-EPI equation included a race multiplier that produced higher eGFR estimates for Black patients — which potentially underestimated kidney disease severity and delayed care. The 2021 formula removes this race variable, providing a single equation that applies to all patients. Most major US medical centers adopted the 2021 formula by 2022.
CKD Stages: What Does Your eGFR Mean?
Kidney disease is classified into 5 stages based on eGFR, combined with markers of kidney damage (proteinuria, abnormal urinalysis, imaging, or biopsy):
| CKD Stage | eGFR (mL/min/1.73m²) | Kidney Function | Action |
|---|---|---|---|
| G1 (Normal or High) | ≥90 | Normal or high (only CKD if other damage markers present) | Treat underlying conditions, optimize BP/glucose |
| G2 (Mildly Decreased) | 60–89 | Mildly reduced | Monitor annually, lifestyle modification |
| G3a (Mildly-Moderately Decreased) | 45–59 | Mild to moderate reduction | Nephrology referral recommended, medication review |
| G3b (Moderately-Severely Decreased) | 30–44 | Moderate to severe | Nephrology follow-up, dietary phosphorus/protein adjustment |
| G4 (Severely Decreased) | 15–29 | Severely reduced | Prepare for kidney replacement therapy discussion |
| G5 (Kidney Failure) | <15 | Kidney failure | Dialysis or transplant evaluation |
Important: A single eGFR measurement does not diagnose CKD. By definition, CKD requires evidence of kidney damage or reduced GFR for more than 3 months. A temporary dip in eGFR from dehydration, acute illness, or new medication does not constitute CKD.
The "albuminuria" dimension: eGFR alone doesn't tell the whole story. Kidney disease staging also includes albuminuria — protein in the urine. A patient with eGFR 75 but significant proteinuria (A3 category: >300 mg/g) has a worse prognosis than eGFR 75 with normal protein levels. Always review eGFR alongside urine protein results.
Normal eGFR by Age: What's Expected?
eGFR naturally declines with age — this is a normal part of aging, not a disease. The typical age-related decline:
| Age Group | Average eGFR (mL/min/1.73m²) | Notes |
|---|---|---|
| Under 40 | 120–130 | Peak kidney function |
| 40–49 | 105–115 | Gradual decline begins |
| 50–59 | 90–105 | ~1 mL/min/year decline |
| 60–69 | 75–90 | Accelerating in some |
| 70–79 | 60–75 | Often borderline Stage 2 |
| 80+ | 45–60 | Many healthy elderly in Stage 3a by formula |
This age-related decline is why "Stage G3a" in a healthy 82-year-old with no proteinuria and normal creatinine trajectory means something very different from Stage 3a in a 45-year-old with diabetes. Context matters. An 80-year-old with stable eGFR of 50 for 10 years is fundamentally different from a 50-year-old whose eGFR has dropped from 90 to 50 over 2 years.
What Causes Low eGFR?
eGFR can be reduced by acute (temporary) or chronic (permanent) causes:
Acute causes (reversible with treatment):
- Dehydration: The most common cause of a temporary eGFR dip in otherwise healthy people. Drink 2–3L of water and retest.
- NSAIDs (ibuprofen, naproxen): Reduce blood flow to the kidneys with regular use. Avoid chronic use if you have CKD.
- ACE inhibitors/ARBs in setting of dehydration: These blood pressure medications reduce filtration pressure; safe when hydrated.
- Urinary obstruction: Kidney stones, enlarged prostate, or tumors blocking urine flow can cause acute kidney injury.
- Sepsis or severe illness: Acute kidney injury (AKI) in critically ill patients; often reversible.
Chronic causes (CKD):
- Diabetes mellitus (Type 1 and 2): #1 cause of CKD worldwide. High blood glucose damages glomerular capillaries (diabetic nephropathy).
- Hypertension: #2 cause. Persistent high blood pressure damages small blood vessels in kidneys.
- Glomerulonephritis: Immune-mediated kidney inflammation; includes IgA nephropathy, lupus nephritis, and others.
- Polycystic kidney disease (PKD): Genetic condition; cysts replace functional kidney tissue over decades.
- Chronic UTIs or recurrent kidney infections
- Long-term use of nephrotoxic medications: Lithium, calcineurin inhibitors, some chemotherapy agents.
How to Protect Your Kidneys: Evidence-Based Prevention
Kidney disease is largely preventable and its progression can be slowed significantly:
- Control blood pressure: Target below 130/80 mmHg. RAAS inhibitors (ACE inhibitors, ARBs) have specific kidney-protective effects beyond BP reduction and are first-line for CKD with proteinuria.
- Control blood sugar: Intensive glycemic control reduces diabetic nephropathy progression. Every 1% reduction in HbA1c reduces microvascular complications (including nephropathy) by 25–40%.
- SGLT2 inhibitors: Medications like empagliflozin and dapagliflozin have demonstrated landmark reductions in CKD progression (30–50% reduction in kidney failure) in multiple large trials. Now recommended for CKD with or without diabetes in many guidelines.
- Avoid nephrotoxins: NSAIDs, contrast dye (with precautions), aminoglycoside antibiotics, and herbal supplements (some traditional remedies contain aristolochic acid — highly nephrotoxic).
- Stay hydrated: Chronic mild dehydration stresses the kidneys over decades. 8–10 cups of water daily is reasonable for most adults.
- Low-sodium diet: Reduces blood pressure and proteinuria. Target <2,300 mg sodium/day (about 1 teaspoon of salt).
- Moderate protein intake: High-protein diets (especially animal protein) increase filtration demand. For CKD stage 3+, protein restriction of 0.6–0.8 g/kg/day may slow progression.
- Regular exercise: Aerobic exercise reduces cardiovascular risk (the #1 cause of death in CKD patients) and modestly improves eGFR over time.
- Quit smoking: Smoking accelerates CKD progression — smokers with CKD lose eGFR 2–4× faster than non-smokers.
eGFR and Exercise: What Runners Need to Know
Running and intense exercise have complex, mostly beneficial effects on kidney function:
Acute effects (temporary, normal): During intense exercise, blood is redirected to working muscles, temporarily reducing kidney perfusion by 20–40%. This can transiently lower eGFR and increase creatinine levels for 12–48 hours after hard runs. Always avoid getting bloodwork done immediately after a race or hard workout — wait at least 48 hours for an accurate creatinine/eGFR reading.
Exercise-induced proteinuria: Temporary protein in urine after hard exercise is common and benign in healthy athletes. It resolves within hours. Persistent proteinuria (at rest, not after exercise) is the clinically significant finding that warrants investigation.
Rhabdomyolysis: Extreme exercise (ultra-marathon finishing, military selection) can cause rhabdomyolysis — muscle breakdown that releases myoglobin, which can block kidney tubules. Warning signs: dark (cola-colored) urine, extreme muscle pain, significantly elevated creatine kinase (CK). Requires urgent IV hydration and medical evaluation.
Long-term benefits: Regular moderate aerobic exercise (running 3–5x/week) is associated with better kidney function preservation over decades, improved blood pressure, and cardiovascular outcomes — all of which reduce CKD progression risk. Runners have lower rates of CKD than sedentary individuals in epidemiological studies.
"The elimination of race from GFR estimation equations is an important step toward reducing health disparities and ensuring equitable care for all patients with kidney disease."
💡 Did you know?
- You can lose up to 90% of kidney function before experiencing significant symptoms. The kidneys have enormous reserve capacity — this is why early detection through eGFR testing is so important.
- Each kidney contains approximately 1 million nephrons (filtering units). You're born with all you'll ever have — kidneys cannot regenerate nephrons once they're lost.
- The average creatinine level varies by muscle mass. A muscular male bodybuilder may have a creatinine of 1.3 mg/dL with perfectly normal kidney function, while an elderly woman with very little muscle mass might have CKD with a creatinine of only 0.9 mg/dL. This is why eGFR (which adjusts for age and sex) is more informative than raw creatinine.
Frequently Asked Questions
What is a normal eGFR level?
For adults under 60, a normal eGFR is typically 90 mL/min/1.73m² or above. For adults over 70, values of 60–75 may be normal age-related decline without disease. eGFR below 60 for more than 3 months, combined with other markers of kidney damage, indicates chronic kidney disease (CKD Stage 3 or higher). A single low eGFR reading is not diagnostic — confirm with a repeat test 3+ months later.
What creatinine level indicates kidney disease?
There is no single creatinine threshold — it must be interpreted in context of age, sex, muscle mass, and trends over time. Generally: creatinine above 1.2 mg/dL (106 µmol/L) in women or above 1.5 mg/dL (133 µmol/L) in men warrants investigation. A rapidly rising creatinine (doubling over weeks) is an emergency regardless of absolute value. The eGFR formula provides a more clinically useful interpretation than raw creatinine alone.
Can eGFR improve?
Yes, especially if the cause is treatable. Correcting dehydration, stopping nephrotoxic medications, treating urinary obstruction, optimizing blood pressure, and controlling blood sugar can all improve eGFR substantially. In early CKD (stages 1–3), aggressive risk factor control can stabilize eGFR and sometimes improve it. Advanced CKD (stages 4–5) generally involves irreversible loss of nephrons, where the goal is to slow further decline rather than reverse it.
How is eGFR different from GFR?
GFR (Glomerular Filtration Rate) is the actual filtration rate, measured using clearance techniques with inulin or iohexol infusion — highly accurate but invasive and expensive. eGFR ("estimated" GFR) is calculated from the creatinine blood test using a validated mathematical formula (CKD-EPI 2021). It is less precise for any individual (accuracy of ±15–20 mL/min) but practical for routine clinical use. True GFR measurements are reserved for living donor kidney evaluation and research settings.
Should I avoid protein before an eGFR test?
Avoid very high protein meals (large steaks, protein shakes) in the 24 hours before a blood test — these temporarily raise creatinine levels. A normal diet is fine. More importantly, avoid intense exercise for 48 hours before the test, as exercise transiently raises creatinine. Fasting is not required for a creatinine/eGFR blood test.
When should I see a nephrologist about my eGFR?
Referral guidelines vary, but generally: eGFR below 45 (Stage 3b or lower); eGFR decline of more than 5 mL/min/year; significant proteinuria (urine albumin-to-creatinine ratio above 300 mg/g); unexplained hematuria (blood in urine); eGFR below 30 regardless of trend. Your primary doctor can manage early CKD (stages 1–3a) with risk factor control; stages 3b–5 typically benefit from nephrology co-management.