Estimate glomerular filtration rate using the CKD-EPI 2021 equation. GFR is the primary measure of kidney function — the number your nephrologist tracks.
GFR measures how well your kidneys filter blood — in mL/min/1.73m². Normal is 90+. Below 60 sustained for 3+ months = chronic kidney disease per KDIGO criteria. This calculator uses the CKD-EPI 2021 equation, which removed the race variable from earlier versions.
Written by Ash K · Last updated: June 2026 · Sources cited below
Your GFR (glomerular filtration rate) measures how well your kidneys filter waste from your blood. It's the single most important number in kidney health — the one your nephrologist uses to diagnose chronic kidney disease (CKD) stages and track progression.
Enter your creatinine level, age, and sex. This calculator uses the CKD-EPI 2021 equation — the current standard recommended by KDIGO and NKF, which removed the race variable from earlier versions.
Key Takeaway: GFR measures how many milliliters of blood your kidneys filter per minute. Normal GFR is 90+ mL/min/1.73m². GFR below 60 sustained for 3+ months indicates chronic kidney disease. The CKD-EPI 2021 equation — used by this calculator — is the current clinical standard.
GFR stands for glomerular filtration rate. "Glomerular" refers to the glomeruli — tiny filtering units in your kidneys (about 1 million per kidney). Each filters blood through a mesh of capillaries, removing waste products (creatinine, urea, toxins) while retaining proteins and blood cells.
Your GFR reflects total kidney filtration capacity. Higher = better filtration. Lower = declining kidney function. The number is estimated from your blood creatinine level, since creatinine is produced at a roughly constant rate and cleared almost entirely by the kidneys.
| GFR (mL/min/1.73m²) | Stage | Kidney Function | What it means |
|---|---|---|---|
| 90+ | G1 | Normal or high | Healthy kidneys (if no other markers of damage) |
| 60–89 | G2 | Mildly decreased | May be normal for age; monitor if other risk factors |
| 45–59 | G3a | Mild-to-moderate decrease | CKD confirmed; monitor progression |
| 30–44 | G3b | Moderate-to-severe decrease | Specialist referral typically recommended |
| 15–29 | G4 | Severely decreased | Preparation for possible dialysis or transplant |
| Below 15 | G5 | Kidney failure | Dialysis or transplant generally required |
Source: KDIGO 2024 Clinical Practice Guideline for CKD.
Warning: GFR below 60 sustained for 3 or more months meets the diagnostic criteria for chronic kidney disease. However, a single GFR below 60 can reflect dehydration, medication effects, or lab variation — not necessarily CKD. Your provider will repeat the test before diagnosing.
This calculator uses the CKD-EPI 2021 equation published by Inker et al. in the New England Journal of Medicine (2021). This version removed the race coefficient that was present in the original 2009 equation, following recommendations from a joint NKF-ASN task force.
The formula uses three variables: serum creatinine, age, and sex. It is more accurate than the older MDRD equation across all GFR ranges, particularly above 60 mL/min where MDRD consistently underestimates GFR.
Note: The 2021 equation removed race as a variable because race is a social construct, not a biological one. Individual variation in creatinine production relates to muscle mass, diet, and health — not race. Using race in the equation led to systematic overestimation of GFR in Black patients, potentially delaying referral to nephrology.
Factors That Can Temporarily Affect GFR Readings
Creatinine level is the direct input. Creatinine is a waste product of muscle metabolism, so anything that changes muscle mass or creatinine production affects the estimate:
Muscle mass — highly muscular individuals produce more creatinine, which can make GFR appear lower than actual kidney function. Dehydration temporarily concentrates creatinine, lowering estimated GFR. Medications (trimethoprim, cimetidine) can raise creatinine without affecting actual kidney function. High-protein meals can temporarily raise creatinine.
Age — GFR naturally declines with age. A GFR of 75 in a 25-year-old is concerning; a GFR of 75 in a 75-year-old may be age-appropriate. The KDIGO guidelines acknowledge that mild GFR decline with aging is physiological, not pathological.
For age-specific normal ranges, see our normal GFR by age guide.
Tip: If your creatinine or GFR result seems inconsistent with your health (e.g., you're a muscular athlete with an unexpectedly low GFR), ask your provider about cystatin C — an alternative biomarker unaffected by muscle mass. Cystatin C-based GFR estimation is recommended by KDIGO as a confirmatory test.
KDIGO guidelines recommend referral to nephrology when GFR falls below 30 (Stage G4), or at higher GFR levels if there is rapid decline (sustained drop of more than 5 mL/min/year), persistent proteinuria, hematuria of renal origin, or CKD with difficult-to-control hypertension.
Bottom Line: GFR is the primary measure of kidney function. Normal is 90+. Below 60 for 3+ months = CKD. This calculator uses the current CKD-EPI 2021 equation (no race variable). A single value doesn't diagnose anything — your provider interprets GFR alongside urinalysis, imaging, and clinical context.
What GFR level indicates kidney disease?
GFR below 60 mL/min/1.73m² sustained for 3 or more months meets KDIGO diagnostic criteria for chronic kidney disease. A single reading below 60 requires confirmation with repeat testing.
What is a normal GFR for my age?
GFR naturally declines approximately 1 mL/min/year after age 40. At age 30, normal GFR is typically 90–120. At age 70, 60–90 may be age-appropriate. See our normal GFR by age guide for detailed ranges.
Is the GFR calculator accurate?
The CKD-EPI 2021 equation estimates GFR within ±20–30% of measured GFR for most people. It's less accurate for extremes of body composition (very muscular or very underweight). For greater accuracy, your provider can order a cystatin C-based GFR or a measured GFR using iohexol clearance.
What affects GFR besides kidney function?
Dehydration, high-protein meals, muscle mass, certain medications (trimethoprim, cimetidine), and acute illness can all affect creatinine levels and therefore estimated GFR without reflecting true kidney function changes.
This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your health.