ReckonBoxHow the eGFR calculator works
Estimated glomerular filtration rate is a calculation of how much blood your kidneys filter each minute, standardised to a body surface area of 1.73 square metres. Enter a serum creatinine from a blood test along with age and sex, and this tool returns the figure using the 2021 CKD-EPI creatinine equation.
There is no race field on this page. That absence is the point, and it's worth explaining rather than leaving unremarked.
Why race came out of the equation
The 2009 equation applied a coefficient that raised estimated GFR for patients recorded as Black, and the 2021 revision removed it. A joint task force of the National Kidney Foundation and the American Society of Nephrology recommended race-free equations in 2021, advising that MDRD and CKD-EPI 2009 be replaced immediately.
A higher estimated GFR makes kidney function look better than it is. Published analysis of the change puts the national scale at 584,000 Black adults reclassified into more advanced chronic kidney disease stages and 41,800 becoming newly eligible for nephrologist referral. The same review records that Black individuals spend almost twice as long on dialysis and transplant waitlists as White individuals, and describes race as a social construct whose presence in a clinical algorithm is itself a form of discrimination.
MDCalc states the direction of the change plainly: for the same creatinine, the 2021 equation gives a lower GFR for Black patients and a higher one for non-Black patients.
Some ranked calculators haven't caught up. One of them still presents a race selector offering "White / Other" or "Black / African American", alongside MDRD, without saying anywhere that MDRD has been superseded. NIDDK keeps its own 2009 calculator online but labels the page "previous" and states that it exists for comparison during the transition.
The equation
eGFR = 142 x min(Scr/k, 1)^a x max(Scr/k, 1)^-1.200 x 0.9938^age x 1.012 if female, where Scr is standardised serum creatinine in mg/dL.
| Variable | Female | Male |
|---|---|---|
| k (kappa) | 0.7 | 0.9 |
| a (alpha) | -0.241 | -0.302 |
| Final multiplier | 1.012 | none |
A 50-year-old man with a creatinine of 1.0 mg/dL lands at 92 mL/min/1.73 m2. The same creatinine in a 50-year-old woman gives 69, because the lower kappa changes which branch of the equation applies.
Creatinine reported in umol/L converts at 88.4 umol/L per mg/dL, and the calculator accepts either.
A number is not a diagnosis
Chronic kidney disease requires either an eGFR under 60 or a urine albumin-to-creatinine ratio of 30 mg/g or higher, with the finding persisting for at least three months. That definition comes from the National Kidney Foundation, and a single eGFR reading satisfies no part of it.
One blood test on one day gives you one number, with no albuminuria measurement and no repeat at three months. A result under 60 is a reason to talk to a doctor, and a result above 60 does not rule kidney disease out, because the albuminuria half of the definition is untouched by this calculation.
| Category | eGFR | Description |
|---|---|---|
| G1 | 90 and above | Normal or high |
| G2 | 60 to 89 | Mildly decreased |
| G3a | 45 to 59 | Mildly to moderately decreased |
| G3b | 30 to 44 | Moderately to severely decreased |
| G4 | 15 to 29 | Severely decreased |
| G5 | Under 15 | Kidney failure |
Where the estimate goes wrong
Creatinine is a muscle breakdown product, so anything that shifts muscle mass shifts the estimate without the kidneys having changed at all. Very high or very low muscle mass, amputation, pregnancy, acute illness and certain medications all interfere.
NIDDK is direct that creatinine alone isn't the best available basis: combining creatinine with cystatin C is preferred and more accurate. This tool ships the creatinine equation because the cystatin C coefficients aren't published on any page used to build it, and reproducing a clinical equation from memory isn't something we'll do.
What this calculator does not do
MDRD and CKD-EPI 2009 are absent by choice. Shipping them would mean reintroducing a race input that the field removed for documented reasons, and offering a reader the option to compute a number their clinician has stopped using.
There's no diagnosis or stage verdict here either. Staging needs albuminuria and a repeat reading, and interpreting either belongs with a nephrologist or GP.
Results are estimates and not medical advice. An eGFR is one input among several that a clinician reads alongside your history, your urine and repeat testing. For related measures, the BMI calculator covers body composition context and the protein calculator discusses the kidney question that often follows a low reading.
Frequently asked questions
What is eGFR? Estimated glomerular filtration rate is a calculation of how much blood the kidneys filter per minute, adjusted to a standard body surface area of 1.73 square metres. It is estimated from a blood creatinine measurement together with age and sex, and reported in mL/min/1.73 m2.
Why does this calculator not ask for race? Because the equation no longer uses it. The 2009 equation applied a coefficient that raised estimated GFR for patients recorded as Black, and a joint National Kidney Foundation and American Society of Nephrology task force recommended race-free equations in 2021, advising immediate replacement of MDRD and CKD-EPI 2009. NIDDK still hosts the older calculator but labels it previous and keeps it only for comparison.
What difference did removing race make? A large one. For the same creatinine, the 2021 equation estimates a lower GFR for Black patients and a higher one for non-Black patients than the equation it replaced. Applied nationally in the US, published analysis puts the change at 584,000 Black adults reclassified into more advanced chronic kidney disease stages and 41,800 becoming newly eligible for nephrologist referral.
Does an eGFR under 60 mean I have kidney disease? Not on its own. The National Kidney Foundation defines chronic kidney disease as either an eGFR under 60 or a urine albumin-to-creatinine ratio of 30 mg/g or more, with the finding persisting for at least three months. A single reading on a single day meets neither the repeat requirement nor the albuminuria half of the definition.
What are the GFR categories? G1 is 90 and above, described as normal or high. G2 is 60 to 89, mildly decreased. G3a is 45 to 59 and G3b is 30 to 44, moderately decreased. G4 is 15 to 29, severely decreased, and G5 is under 15, kidney failure. These describe a filtration level, not a diagnosis by themselves.
Is creatinine the most accurate basis? Not the most accurate available. NIDDK states that using both creatinine and cystatin C to estimate GFR is preferred and more accurate than serum creatinine alone. This calculator implements the creatinine equation because the cystatin C coefficients are not published on the pages used to build it.
What makes an eGFR estimate unreliable? Creatinine comes from muscle, so anything that changes muscle mass or creatinine handling moves the estimate without the kidneys changing. That includes very high or very low muscle mass, amputation, pregnancy, acute illness and some medications. The result is an estimate of filtration, not a measurement of it.