GFR Calculator

About the GFR Calculator

A GFR calculator estimates the glomerular filtration rate (eGFR) — the primary measure of kidney function used worldwide to diagnose and stage chronic kidney disease (CKD). The eGFR represents how many millilitres of blood the kidneys filter per minute per 1.73 m² of body surface area. A normal eGFR is ≥ 90 mL/min/1.73 m²; below 60 for 3+ months indicates chronic kidney disease; below 15 indicates kidney failure requiring dialysis or transplant. Our calculator uses the CKD-EPI 2021 creatinine equation — the current gold standard endorsed by KDIGO (Kidney Disease: Improving Global Outcomes) and adopted by major laboratories in the USA, UK, Australia, Canada, and worldwide. The 2021 equation is race-free (no longer includes a race variable), more accurate across diverse populations, and is now the standard in most clinical laboratories. Enter serum creatinine (in μmol/L — the SI unit used in most countries outside the USA), age, and sex to get your eGFR and the corresponding CKD stage with clinical interpretation. This tool is for informational purposes — always confirm with your healthcare provider.

How It Works

CKD-EPI 2021 equation: eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(-1.200) × 0.9938^age × sex factor. Where: Scr = serum creatinine in mg/dL (to convert from μmol/L: divide by 88.42); κ = 0.7 (females) or 0.9 (males); α = −0.241 (females) or −0.302 (males); sex factor = 1.012 (females) or 1.0 (males). CKD staging by eGFR: G1: ≥ 90 (normal); G2: 60-89 (mildly decreased); G3a: 45-59 (mild-moderate); G3b: 30-44 (moderate-severe); G4: 15-29 (severely decreased); G5: < 15 (kidney failure). Example: female, age 55, creatinine 100 μmol/L = 1.131 mg/dL. Scr/κ = 1.131/0.7 = 1.616. Since > 1: eGFR = 142 × 1^(-0.241) × 1.616^(-1.200) × 0.9938^55 × 1.012 = 142 × 1 × 0.755 × 0.713 × 1.012 = 77.2 mL/min/1.73m². CKD Stage G2 — mildly decreased.

Tips & Best Practices

• ✓Normal creatinine varies: the reference range for serum creatinine is 60-110 μmol/L (males) and 45-90 μmol/L (females) in most laboratories. Creatinine alone is a poor marker of kidney function because it depends on muscle mass — a muscular man with early kidney disease may have "normal" creatinine while his eGFR is significantly reduced.
• ✓CKD requires confirmation: a single eGFR below 60 does not diagnose CKD. KDIGO requires eGFR < 60 for at least 3 months, or any marker of kidney damage (proteinuria, abnormal urinalysis, imaging findings) for CKD diagnosis. Acute illness, dehydration, and medications can cause transient eGFR reduction.
• ✓Creatinine unit conversion: US labs often report in mg/dL; UK, Australian, and most international labs use μmol/L. To convert: μmol/L × 0.0113 = mg/dL. Or: mg/dL × 88.42 = μmol/L. The calculator accepts μmol/L (divide by 88.42 internally to apply the CKD-EPI formula).
• ✓Cystatin C-based eGFR: the CKD-EPI cystatin C equation provides an alternative eGFR calculation less affected by muscle mass — better for sarcopenic elderly patients, amputees, and those with unusual muscle mass. If available, cystatin C or combined creatinine+cystatin C eGFR is more accurate than creatinine alone.

Who Uses This Calculator

Patients with chronic kidney disease tracking eGFR progression over time. Individuals who have received a creatinine lab result and want to understand what it means for their kidney function. Healthcare students and practitioners learning to calculate and interpret eGFR. People with diabetes, hypertension, or cardiovascular disease — conditions that increase CKD risk — monitoring their kidney function at home between clinical appointments.