GFR Calculator - Estimate Your Glomerular Filtration Rate (eGFR)

True GFR requires a precise, often cumbersome lab procedure using a filtering agent like inulin or a radioactive tracer. It's the gold standard but rarely done in routine clinical practice because it's expensive and time-consuming.

eGFR, or estimated GFR, is the practical stand-in. It uses a mathematical equation that takes your serum creatinine level along with factors like age, sex, and sometimes race to estimate what your actual GFR likely is. The estimate is accurate enough for clinical decision-making in the vast majority of patients.

When you get kidney function results from a lab panel, the number reported is almost always an eGFR. The two terms get used interchangeably in everyday conversation, but technically they're different things. For most people, the distinction doesn't change how the number should be interpreted.

For adults 18 and older, the calculator uses either the CKD-EPI or MDRD equation. CKD-EPI is the default and the one most labs and clinical guidelines recommend today. It tends to be more accurate at higher GFR values, which matters when you're trying to catch early kidney function decline before it becomes a serious problem.

You'll enter your serum creatinine (in mg/dL or µmol/L depending on what your lab reports), your age in years, and your biological sex. Some versions of the older equations also ask for race, though newer race-free equations are increasingly being adopted. The result will appear as a single number in mL/min/1.73m².

Kidney function in children is calculated differently. Kids' bodies are still developing, so adult equations don't apply. The Schwartz formula (also called the bedside Schwartz or revised Schwartz equation) is the standard method for estimating GFR in pediatric patients.

It uses the child's serum creatinine and their height in centimeters. The formula is: eGFR = (0.413 × height in cm) / serum creatinine in mg/dL. This revised version replaced the older Schwartz formula after the CKID study showed the original consistently overestimated kidney function in children.

Normal GFR in children varies by age and body size, so pediatric results should always be interpreted by a pediatric nephrologist or the child's primary care provider rather than compared directly to adult reference ranges.

Serum creatinine is the key input. Creatinine is a waste product produced by muscle metabolism, and healthy kidneys filter it out of the blood at a relatively constant rate. When kidneys aren't working well, creatinine builds up. Your value comes from a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP).

• Age: Kidney function naturally decreases with age, so the formulas account for this. Older adults typically have lower eGFR values even without kidney disease.
• Sex: Men generally have more muscle mass than women, which means they produce more creatinine. The equation adjusts for this so a given creatinine level isn't interpreted the same way for both sexes.
• Race (in some equations): The 2009 CKD-EPI and original MDRD equations included a race coefficient for Black patients, based on observed differences in creatinine production. The newer 2021 CKD-EPI equation removed this coefficient, and many institutions have transitioned to that version. If your calculator asks for race, check which equation version it's using.

Units matter too. Make sure you're entering creatinine in the unit your calculator expects, either mg/dL (common in the U.S.) or µmol/L (common elsewhere). A mismatch will give you a wildly incorrect result.

The CKD-EPI equation (Chronic Kidney Disease Epidemiology Collaboration) was developed in 2009 and has been the preferred formula in most major nephrology guidelines since. It was designed to address a key weakness of the MDRD equation: poor accuracy in people with normal or near-normal kidney function.

The math uses a two-slope model. The equation's relationship between creatinine and eGFR changes depending on whether your creatinine is above or below a certain threshold (0.7 mg/dL for women, 0.9 mg/dL for men). This makes it more precise across a wider range of kidney function levels.

The 2021 update removed the race variable, producing what's now called the CKD-EPI 2021 equation. It performs comparably to the 2009 version overall, and it avoids the ethical concerns around encoding race as a biological variable. Many hospitals and labs have already switched to it.

The MDRD equation (Modification of Diet in Renal Disease) came first, developed in the 1990s from a study of patients who already had CKD. For years it was the standard, and it's still used in some labs today.

It works reasonably well for detecting moderate to severe kidney disease but tends to underestimate GFR in people with healthy or mildly reduced kidney function. That's a real limitation because it means some people with early kidney decline might get a falsely reassuring result, while healthy people might get an unnecessarily low-looking number.

If your lab report shows an eGFR marked as "MDRD" or shows values like ">60" without a precise number above that threshold, that's a tell. MDRD wasn't designed to report accurately above 60 mL/min/1.73m², so many labs just cap the result there. CKD-EPI doesn't have that limitation.

For most adults, CKD-EPI 2021 is the right choice. It's more accurate across the full range of kidney function, it doesn't require a race input, and it's what the major kidney disease organizations currently recommend, including the National Kidney Foundation and the American Society of Nephrology.

If you're reviewing a lab result and want to compare it against this calculator, check which equation your lab used. The difference between formulas can shift your eGFR by a few points, which matters when you're near a diagnostic threshold.

Stages G3 through G5 are where most active management happens. By G4, a nephrologist is usually involved, and conversations about dialysis or transplant options begin. Stages G1 and G2 are often caught only through routine screening, which is one reason those screenings matter for people with diabetes, high blood pressure, or a family history of kidney disease.

There's no single number where a switch flips from safe to dangerous, but there are thresholds that signal serious concern.

An eGFR below 30 mL/min/1.73m² (Stage G4) means the kidneys are working at less than a third of normal capacity. At this point, waste products and fluid can accumulate in the body, blood pressure becomes harder to control, and complications like anemia, bone disease, and cardiovascular risk increase significantly. Patients at this stage are typically under active nephrology care.

An eGFR below 15 mL/min/1.73m² is kidney failure (Stage G5). Without dialysis or a kidney transplant, the body can't maintain the chemical balance it needs to function. This is a medical emergency when it arrives suddenly (acute kidney failure), though in CKD it usually develops gradually over months or years.

Rapid decline is also a red flag, even if the absolute number hasn't hit a critical threshold yet. Losing more than 5 mL/min/1.73m² per year is considered fast progression and warrants urgent evaluation. If your eGFR dropped noticeably between two recent tests, bring both results to your doctor rather than waiting for your next scheduled appointment.