GFR Calculator

What is GFR, what counts as a normal value, and what a GFR calculator shows

The kidneys filter waste out of the blood continuously. GFR, or gfr glomerular filtration rate in full, is the medical measure of how much blood the kidneys filter per minute, expressed in mL/min/1.73m² (the 1.73m² normalizes the figure to an average adult body surface area, so people of different sizes can be compared on the same scale). What is normal GFR, and what is the average GFR, are really two versions of the same question, and the commonly cited normal GFR range for healthy adults under 40 is about 100 to 130 mL/min/1.73m² for men and about 90 to 120 mL/min/1.73m² for women, with GFR reference range figures declining gradually with age afterward even in people who have no kidney disease at all. A single eGFR reading below those bands is not automatically abnormal for an older adult; age is one of the biggest drivers of a lower, still-healthy number.

Creatinine is a waste product released into the blood at a fairly steady rate by muscle tissue, and it is normally filtered out by the kidneys. When kidney filtering slows down, creatinine builds up in the blood, so a higher creatinine level generally points to lower kidney function. But creatinine on its own is not a clean measure, because it also depends on how much muscle a person has, and muscle mass varies on average by age and by sex, which is exactly why every formula below uses age and sex as correction factors, not creatinine alone, to turn a raw lab value into a comparable eGFR estimate.

What is normal GFR, in the terms people actually search

What is normal GFR, what is the average GFR, normal GFR by age, normal GFR by age and gender, and gfr normal ranges are all pointing at the same handful of numbers described above: roughly 100 to 130 for men and 90 to 120 for women under 40, declining with age. A normal GFR value for an older adult is legitimately lower than a normal value for a 25-year-old, which is exactly why every formula on this page treats age as an input, not an afterthought. If your real question is how to calculate kidney function or how to compute kidney function from a lab report rather than simply reading a normal gfr value off a chart, that is precisely what entering your creatinine, age and sex into the calculator above does: it functions as a gfr calculator, an egfr calculator, and, informally, a ckd calculator, all from the same three inputs, since a GFR rating below normal is the same underlying signal a CKD stage describes.

Population mean estimated GFR by age

Because GFR declines gradually with age in the general population, commonly cited population studies report an approximate gfr average by age-by-decade even among people with no diagnosed kidney disease. These are rounded, widely reproduced reference figures, not a precise prediction for any one person:

The KDIGO Chronic Kidney Disease stages explained

KDIGO (Kidney Disease: Improving Global Outcomes) publishes the staging bands this calculator uses to describe an eGFR result in plain terms; this is the same gfr stages chart clinicians reference when discussing a result:

• G1, 90 and above: normal or high kidney function.
• G2, 60 to 89: mildly decreased kidney function. Many people in this range have no symptoms at all.
• G3a, 45 to 59: mildly to moderately decreased kidney function.
• G3b, 30 to 44: moderately to severely decreased kidney function.
• G4, 15 to 29: severely decreased kidney function.
• G5, below 15: kidney failure.

A stage on its own is not a diagnosis of chronic kidney disease. Doctors generally look for reduced function, or another sign of kidney damage such as protein in the urine, persisting for three months or more before making that call, and they typically combine eGFR with a urine albumin test, and sometimes an alternative marker called cystatin C, an egfr by cystatin c or cystatin c with egfr result, rather than relying on creatinine-based eGFR alone. The Chronic Kidney Disease stages table shown just above the calculator on this page is a shorter, plain-language Normal/CKD1-CKD5 reference table describing the same underlying eGFR ranges as the six-band G1-G5 list above, just grouped slightly differently (it does not split G3 into G3a/G3b), so the two are meant to be read as two views of the same picture, not two different results.

Measuring GFR directly versus estimating it

Every formula on this page estimates GFR from creatinine; none of them measures it directly. The clinical gold standard for a true, directly measured GFR is inulin clearance: inulin is a substance the kidneys filter out completely without reabsorbing or secreting any of it, so measuring how quickly it clears the blood gives an essentially exact GFR figure. It is also expensive, slow, and involves an IV infusion and multiple timed blood draws, which is why it is reserved for research and specific clinical situations rather than routine care.

A more practical direct measurement, creatinine clearance from a timed urine collection, is sometimes used instead, but it carries a well-documented caveat worth stating plainly: because creatinine is filtered by the kidneys but also secreted a small amount directly into the urine by the kidney tubules, creatinine clearance vs GFR comparisons consistently show creatinine clearance running about 10 to 20% higher than true GFR, an overestimation that gets worse as kidney function declines. The creatinine-based formulas below are built and statistically corrected to estimate true GFR itself, not creatinine clearance, which is part of why they are preferred over a raw creatinine clearance figure in most clinical settings today.

The formulas themselves

All figures below use serum creatinine (SCr) in mg/dL. The worked comparison further down this page runs one shared patient, a 50-year-old man with SCr = 0.9 mg/dL who is not Black, through all three adult formulas side by side.

• MDRD 4-Variable (Levey et al., 2006, IDMS-traceable version), with a sex factor of 0.742 applied if female and a race factor of 1.212 if Black (each is 1 otherwise):
  eGFR = 175 SCr^(-1.154) Age^(-0.203) f_(sex) f_(race)
• CKD-EPI (2021 creatinine equation, race-free; this page's default result): with kappa (κ) = 0.7 (female) or 0.9 (male), alpha (α) = -0.241 (female) or -0.302 (male), and a sex factor of 1.012 (female) or 1 (male), written f_sex below:
  eGFR = 142 min (SCr/(κ), 1)^α; max (SCr/(κ), 1)^(-1.2) 0.9938^(Age) f_(sex)
• Mayo Quadratic (Rule et al., Ann Intern Med 2004; no race term; SCr below 0.8 is floored to 0.8):
  eGFR = exp (1.911 + 5.249/SCr - 2.114/(SCr^2).;. - 0.00686 · Age - 0.205 · [female])
• Bedside Schwartz (Schwartz et al., 2009; this page's Children calculator), one constant, k = 0.413, across its whole roughly 1-to-16-years age range, with no separate age or sex term:
  eGFR = 0.413 × (height (cm))/SCr
  The original (1976) Schwartz formula instead varies k by age and sex (0.33 for a low-birth-weight infant under 1, 0.45 for a full-term infant under 1, 0.55 for children and adolescent females, or 0.70 for adolescent males 13-21); this page's Children calculator uses the newer, single-constant bedside version above since it only asks for height and creatinine.

Worked comparison. For a 50-year-old man, SCr = 0.9 mg/dL, not Black: MDRD gives 175 × 0.9^-1.154 × 50^-0.203 ≈ 89.3 mL/min/1.73m²; CKD-EPI 2021 gives ≈ 104.0 mL/min/1.73m²; Mayo Quadratic gives exp(1.911 + 5.249÷0.9 − 2.114÷0.81 − 0.343) ≈ 120.3 mL/min/1.73m². Three published, peer-reviewed formulas, the exact same lab value, age, and sex, and three meaningfully different numbers, MDRD landing in stage G2 while Mayo Quadratic lands comfortably in G1. This spread is a well documented, known property of these formulas, not a sign that any one of them is broken: MDRD is specifically known to underestimate true GFR at higher, more normal filtration rates, which the Mayo Quadratic formula was built afterward to correct. Enter the same three numbers into the calculator above to see all three computed live.

Why this page defaults to CKD-EPI 2021

The version of the CKD-EPI equation published in 2009 included a coefficient that raised the calculated eGFR for patients identified as Black, based on population studies that found Black patients tended to have higher measured creatinine at a given true GFR. In the years that followed, clinical and scientific reviewers found that treating race as a biological variable in this way was not well justified, and that it carried a real cost: by adjusting the number upward, it could make a Black patient's kidney disease look less severe on paper than it actually was. That in turn was linked to delayed specialist referrals, delayed dialysis planning and delayed transplant eligibility for some patients. In response, a joint task force of major U.S. kidney and laboratory medicine organizations recommended removing race from the equation entirely, and the 2021 CKD-EPI creatinine equation shown as this page's primary result reflects that change: it calculates eGFR from creatinine, age and sex only, with no race-based adjustment. MDRD's optional Race choice above is shown only as a reference figure against MDRD's own original, published form, for exactly the comparison the worked example above walks through, never as a recommendation to use it that way.

A repeated disclaimer, because this matters

This calculator does not diagnose kidney disease and does not replace a doctor's evaluation. It takes a creatinine value you already have from a lab test and applies a published formula to it, nothing more. Lab results can vary between labs and between test days, and a single number cannot capture your full medical history. Any concern about your kidney function, whatever this calculator shows, belongs in a conversation with a doctor and real lab testing, not on this page.