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. In health, fitness, and nutritional planning, tracking personal metrics provides a scientific, data-driven baseline for setting realistic wellness goals. Human metabolism and body composition are highly individual, influenced by factors such as age, biological sex, height, activity level, and underlying genetics. While standard equations (such as the Mifflin-St Jeor or Navy Body Fat equations) offer valuable population-level screening guidelines, they should be interpreted alongside other markers of health under the guidance of qualified professionals. Using this calculator allows you to monitor changes over time, helping you calibrate your daily caloric intake, macronutrient balance, or hydration schedule to support sustainable lifestyle improvements and long-term vitality. Furthermore, individual circumstances and local regulations can significantly impact the practical application of these figures. Users in the USA, Canada, the United Kingdom, Australia, and New Zealand often face different regional guidelines, tax brackets, or baseline measurements (such as USDA zones, CRA guidelines, HMRC allowances, or ATO schedules) that should be factored into any serious planning. By entering your specific parameters into this calculator, you can model multiple scenarios side by side to see how minor changes in inputs affect the overall outcome. This makes the tool an indispensable asset for regular monitoring and long-term goal setting, helping you adjust your strategies as your needs evolve over time.

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. To compute this value manually, follow these standard steps: 1. Identify all the required input variables (such as base values, rates, dimensions, or constants) and convert them to matching units. 2. Apply the primary mathematical formula or conversion factor designated for this specific calculation. 3. Perform the arithmetic operations step by step, ensuring you strictly follow the standard order of operations (PEMDAS/BODMAS). 4. Verify the result by running the calculation in reverse or checking against known reference tables. By following this structured methodology, you can verify your results and gain a deeper understanding of the relationships between the different variables involved in the calculation.

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. Common practical scenarios for this tool include: - Professional scenarios: Engineers, financial analysts, accountants, health practitioners, and educators use this calculation to verify data, draft official reports, and double-check manual calculations quickly. - Consumer and everyday scenarios: Homeowners, students, fitness enthusiasts, and travelers use the tool to make quick estimates on the go, budget for upcoming projects, and track personal goals. - Educational learning: Students and teachers use this tool as a step-by-step visual aid to understand mathematical formulas and verify homework answers.