GFR Calculator
Estimate kidney function from a serum creatinine result. You get the figure your lab reports, three older equations beside it for comparison, and the Schwartz formula for children.
You can leave this alone. Race does not affect your estimated GFR — that figure uses the race-free 2021 equation. It only changes the two older formulas below, which were published with a Black coefficient that a 2021 NKF–ASN task force found had no biological basis. Why this changed.
All four equations
If you are comparing against a blood test result, the highlighted row is the one to match — it is the equation US laboratories report.
Chronic Kidney Disease Stages
| Stage | GFR Value (mL/min/1.73 m2) |
|---|
The row matching your CKD-EPI figure is highlighted. Normal and CKD1 share the same band — what separates them is evidence of kidney damage, usually albumin in the urine. A figure under 60 has to persist for three months before it counts as chronic kidney disease.
| Equation | Fitted on | Reads best |
|---|---|---|
| CKD-EPI 2021 | The same data, refit without race | What US labs report today |
| MDRD 4-Variable | People who already had kidney disease | Below 60; understates healthy kidneys |
| CKD-EPI (2009) | A broad population including normal function | Across the whole range |
| Mayo Quadratic | A cohort with mostly preserved function | At the high end |
| Bedside Schwartz | Children, using height for muscle mass | Ages 1 to 17 |
The highlighted row is the one your laboratory almost certainly uses, and it is the figure shown at the top of the result. The three below it are the older equations the reference tool implements, kept so you can see how much the choice of formula moves the answer.
| Age | Mean eGFR |
|---|
Filtration falls with age at roughly a millilitre a minute per year after 40, so the same number means different things at 25 and at 75. Staging thresholds are not age-adjusted.
What glomerular filtration rate measures
Each kidney holds around a million glomeruli, tiny tufts of capillary that act as the first filter on your blood. Glomerular filtration rate is the volume they clear per minute, and it is the single most useful number for describing how much working kidney a person has left.
The figure is reported as mL/min/1.73 m2 — millilitres per minute, indexed to a standard body surface area of 1.73 square metres. Without that indexing a large adult and a small one could not be compared, since bigger bodies filter more in absolute terms simply by being bigger.
Almost nobody has their GFR measured directly. Doing it properly means infusing a marker such as inulin or iohexol and timing its clearance across several hours of blood and urine samples, which is accurate and entirely impractical outside research. What laboratories report instead is an estimate from serum creatinine, and every equation on this page is one attempt at making that estimate.
Why creatinine is a useful but imperfect proxy
Creatinine is a waste product of muscle metabolism. It is produced at a fairly steady rate, filtered freely at the glomerulus, and barely reabsorbed, which makes its blood concentration a rough inverse signal of filtration. If the kidneys slow down, creatinine climbs.
The weakness is in the word "muscle". Creatinine production scales with muscle mass, so the same blood level means different things in different bodies. A heavily built weightlifter and a frail eighty-year-old can share a creatinine of 1.1 mg/dL while having very different kidney function. Equations patch over this with age, sex and — in the older versions — race coefficients, which are population averages standing in for a measurement nobody takes.
Several other things move creatinine without touching filtration at all: dehydration, a large meat meal, hard exercise in the previous day or two, and drugs including trimethoprim, cimetidine and cobicistat, which block its secretion into the urine. A single surprising reading is worth repeating before it is worth worrying about.
The four adult equations, and why they disagree
The headline figure uses the 2021 CKD-EPI equation, because that is what a US laboratory prints on a blood test report today and therefore the number most visitors are here to match. The three below it are the older equations, reported alongside rather than hidden, because their disagreement is itself informative.
MDRD (4-variable) came out of the Modification of Diet in Renal Disease study, fitted on people who already had kidney disease. It performs reasonably in that group and systematically under-reports in people with healthy kidneys, which is why many laboratories used to suppress any MDRD result above 60 rather than print it.
CKD-EPI was developed to fix precisely that, using a much broader population that included people with normal function. It is more accurate at the high end and has been the basis of laboratory reporting for over a decade. The version reproduced here is the 2009 one, which carries a race coefficient — see the section below.
The Mayo quadratic equation takes a different shape entirely, using creatinine and its square rather than a single power term, and was built to avoid understating function in healthy kidneys. It tends to give the highest of the three in people with good function, and the three converge as function falls.
142 × min(SCr÷k, 1)a × max(SCr÷k, 1)−1.200 × 0.9938age × 1.012 (female)
k = 0.7 female, 0.9 male · a = −0.241 female, −0.302 male · no race term
MDRD 4-variable
175 × SCr−1.154 × age−0.203 × 0.742 (female) × 1.212 (Black)
CKD-EPI (2009)
base × (SCr ÷ k)a × 0.993age
k = 0.7 female, 0.9 male · a = −0.329 or −0.411 when SCr ≤ k, otherwise −1.209
base = 144 / 141 non-Black female / male, 166 / 163 Black female / male
Mayo quadratic
e(1.911 + 5.249÷SCr − 2.114÷SCr2 − 0.00686×age − 0.205 if female)
with SCr floored at 0.8 mg/dL
Bedside Schwartz, for children
0.413 × height in cm ÷ SCr
The spread shown under the results is worth a glance. A wide spread means creatinine is doing a poor job of pinning down the answer for this particular person, which is a signal to treat any single figure loosely.
The race coefficient, and why it is no longer used
Both MDRD and the 2009 CKD-EPI equation multiply the result upward for Black patients — by 1.212 and by roughly 1.16 respectively. That coefficient came from observations that Black participants in the original studies had higher average creatinine at a given measured filtration rate, an association attributed at the time to differences in muscle mass.
It has since been abandoned. In September 2021 a joint task force of the National Kidney Foundation and the American Society of Nephrology concluded that race is a social rather than a biological category and that the coefficient rested on thin evidence, and it recommended immediate adoption of the 2021 CKD-EPI creatinine equation, which contains no race term. US laboratories moved across, and the task force also urged wider use of cystatin C alongside creatinine where a confirmatory measure is needed.
Practically, the older coefficient raised the reported figure for Black patients, which in some cases delayed a CKD stage classification, a specialist referral, or a place on a transplant waiting list. That is the reason the change mattered rather than being cosmetic.
The Race control on this page therefore does nothing to your headline figure, which uses the 2021 equation. It changes only the two historical formulas below it, and it is kept because removing it would quietly stop those formulas reproducing what they were published to produce. If the number you actually want is the one on your lab report, it is the highlighted row \u2014 and the gap between it and the row beneath it is a fair measure of what the coefficient used to do.
Reading the CKD stages
The staging table splits filtration into bands, but the bands alone do not diagnose anything. The distinction between "Normal" and "CKD1" is not the GFR at all — both sit at 90 or above — it is whether there is separate evidence of kidney damage, most often albumin in the urine.
Below 60 the picture changes: a sustained figure under 60 for three months or more is considered chronic kidney disease regardless of other findings, which is why 60 is the number people remember. Under 15 is kidney failure, the point at which dialysis or transplantation enters the conversation.
Two words in that description carry most of the weight. Sustained means the value has to persist across repeat testing; a single low reading during an illness or a bout of dehydration is not a diagnosis. And chronic distinguishes this from acute kidney injury, which develops over days and often reverses.
GFR falls with age, and that is normal
Filtration peaks in early adulthood and declines gradually from around 40, at a rough average of a millilitre per minute per year. The population figures in the reference card show the shape of it: about 116 in the twenties, 99 in the forties, 75 past seventy.
This creates a real interpretive problem. A GFR of 78 in a healthy 75-year-old is close to the population average for that age, while the same 78 in a 25-year-old would prompt investigation. Staging thresholds are fixed rather than age-adjusted, so a large share of otherwise healthy older adults fall into CKD3 on the number alone — which is one of the standing criticisms of the staging system and a reason albuminuria is measured alongside it.
The children's calculator
Children need a different equation because their creatinine rises naturally as they grow, so an adult formula reads a healthy child as though their kidneys were failing.
The bedside Schwartz formula sidesteps age and sex entirely and uses height, which tracks muscle mass well through childhood. The constant of 0.413 belongs to the 2009 revision, calibrated for creatinine measured by the standardised IDMS-traceable methods laboratories now use — an older version of the same formula used different constants for infants, boys and girls, and applying those to a modern creatinine result gives an inflated answer.
It is least reliable at the two ends: in the first year of life, when kidney function is still maturing, and in adolescents who are close to adult body composition, where the adult equations are starting to become appropriate instead.
What this calculator does not cover
It is an estimate from a blood test, not an assessment of kidney health. It says nothing about albumin in the urine, which guidelines treat as an equal partner to GFR in staging and which can be abnormal while filtration still looks fine. It does not use cystatin C, the confirmatory marker recommended where creatinine is unreliable, nor any cystatin-based equation \u2014 every figure here comes from creatinine alone.
It also assumes a steady state. In acute kidney injury creatinine lags the actual damage by a day or more, so every equation here will overstate function while things are still moving. And an indexed figure is not what pharmacists use for renal drug dosing, which frequently calls for Cockcroft-Gault or an unindexed rate instead.
None of the numbers on this page is a diagnosis. If a result surprises you, the useful next step is a repeat test and a conversation with a doctor, not a decision made from a web page.
Frequently asked questions
What is a normal GFR?
For an adult under 40 the usual range is roughly 100 to 130 mL/min/1.73 m2 in men and 90 to 120 in women. After 40 the figure falls steadily with age, so a reading of 85 means something quite different at 70 than it does at 25. A single value above 60 with no other sign of kidney damage is generally regarded as adequate rather than as a diagnosis of anything.
Why do the four equations give different answers?
Because each was fitted to a different group of people. MDRD was derived from patients who already had kidney disease and is known to understate function in healthy kidneys. The 2009 CKD-EPI equation was fitted across a wider range and behaves better at higher values, and the 2021 version is that same equation refit without race. The Mayo quadratic equation was built specifically to stop underestimating in people with normal function. Where the estimates diverge most is exactly where creatinine is least informative.
Which equation do laboratories actually report?
In the United States most laboratories now report the 2021 CKD-EPI creatinine equation, which contains no race variable. That is the figure shown at the top of this page and highlighted in the results, so it is the one to compare against a blood test report. The three below it — MDRD, the 2009 CKD-EPI and the Mayo quadratic — are older equations kept for comparison, and a lab quoting one of those will differ by a few units.
Why does this calculator ask about race?
Only for the two older equations, which were published with a Black coefficient. Your headline result uses the 2021 equation and ignores the field entirely, so you can leave it alone. The coefficient itself is no longer recommended: in 2021 a joint National Kidney Foundation and American Society of Nephrology task force concluded it lacked biological justification and called for immediate adoption of a race-free equation. It is kept here so the older formulas still reproduce what they were published to produce.
What does mL/min/1.73 m2 mean?
It is a filtration rate indexed to a standard adult body surface area of 1.73 square metres, so that people of different sizes can be compared on one scale. The indexing is also why a very large or very small adult can have their true filtration rate misrepresented, and why drug dosing sometimes uses an unindexed figure instead.
Can a single creatinine test tell me my kidneys are failing?
No. Creatinine reflects muscle mass, hydration, diet and several medications as well as filtration, so one reading in isolation says little. A muscular person can look worse than they are and someone with very little muscle can look better. What matters clinically is the trend across repeated tests, together with a urine albumin measurement, which is why guidelines pair the two.
Why is there a separate calculator for children?
Because the adult equations were fitted on adults and produce nonsense in children, whose creatinine rises naturally as they grow. The paediatric estimate uses the bedside Schwartz formula, which works from height and creatinine and needs neither age nor sex. Height stands in for muscle mass, which is what makes it work across a wide range of ages.
My result changed a lot between two tests. Should I worry?
Possibly, but check the obvious causes first. Dehydration, a heavy protein meal, intense exercise in the previous day or two, and drugs such as trimethoprim or cimetidine all move creatinine without changing filtration. A genuine, sustained fall over months is the pattern that matters. Take any unexpected result to a doctor rather than acting on it yourself.
This calculator is an educational tool, not a diagnosis and not medical advice. Estimated GFR from a single creatinine result cannot establish or rule out kidney disease, and the older equations shown alongside it differ from the 2021 equation that laboratories in the United States report. Never start, stop or change a medication on the basis of a number from this page. Take any unexpected kidney result to a doctor. More about how we build and check these tools is on our About page, and our Privacy Policy explains what we do and do not collect.