GFR Calculator
Estimate your kidney filtration rate from a blood test, using the race-free CKD-EPI 2021 equation.
GFR Calculator — your inputs
- Sex
- Male
- Age
- 30 yrs
- Serum creatinine
- 0.9
- Creatinine unit
- mg/dL (US)
- Weight (optional)
- 70 kg
- Unit system
- Metric
Key takeaways
- eGFR estimates how much blood your kidneys filter each minute, scaled to a standard 1.73 m² body — not to yours.1
- This calculator uses the 2021 race-free CKD-EPI equation. The older versions raised the reported figure for Black patients, which delayed referral and transplant listing, and a joint NKF–ASN task force recommended removing race entirely.2
- One reading is not a diagnosis. Chronic kidney disease requires the change to persist for at least three months, and stages G1 and G2 need another marker of damage — usually albumin in the urine — before they mean anything.3
- Creatinine comes from muscle, so it misleads at the extremes of muscle mass in both directions. That is exactly what cystatin C is for.1
- Around 1 in 7 US adults has chronic kidney disease, and roughly nine in ten of them do not know it — which is why a routine blood test is where this usually surfaces.5
How to use this calculator
Take the serum creatinine value from your blood test result, and set the unit to match your report — US labs print mg/dL, most others print µmol/L.
Enter your age and sex. There is no race input: the 2021 equation removed it.
If your report includes cystatin C, add it. The combined equation is more accurate and is what leads the result.
Understanding your result
eGFR estimates how many millilitres of blood your kidneys filter each minute, normalised to a standard 1.73 m² body. Above 90 is normal; the KDIGO stages below that describe how much filtration has been lost, not how ill you are.
A single reading cannot diagnose chronic kidney disease. That requires the change to persist for at least three months, and G1 and G2 need another marker of kidney damage — usually albumin in the urine — before they mean anything at all.
Creatinine comes from muscle, so a very muscular person can have a low eGFR with healthy kidneys, and someone with little muscle can have a normal-looking eGFR with reduced function. This is exactly what cystatin C is for.
What eGFR actually measures
Glomerular filtration rate is the volume of blood your kidneys clear of waste each minute. Measuring it directly means infusing a marker such as iohexol and sampling repeatedly over several hours, which is accurate, expensive, and almost never done. So it is estimated instead — from a waste product the kidneys clear, and how much of it has built up in the blood.
Creatinine is that waste product. It comes from the normal turnover of creatine in muscle, is produced at a fairly steady rate, and is filtered by the kidneys. If filtration falls, creatinine accumulates. The equation works backwards from that concentration, correcting for age and sex because both change how much creatinine a person generates in the first place.
Why the units end in 1.73 m²
Filtration scales with body size, so results are normalised to a standard body surface area of 1.73 m² — the average for young adults when the convention was set in the 1920s. If your own body surface area is far from that, your kidneys' actual filtration rate differs from the reported one, which matters for some drug dosing.
The KDIGO stages, and what they do not mean
| Stage | eGFR (mL/min/1.73m²) | Description |
|---|---|---|
| G1 (success) | 90 and above | Normal or high |
| G2 (success) | 60 – 89 | Mildly decreased |
| G3a (warning) | 45 – 59 | Mildly to moderately decreased |
| G3b (warning) | 30 – 44 | Moderately to severely decreased |
| G4 (danger) | 15 – 29 | Severely decreased |
| G5 (danger) | Below 15 | Kidney failure |
This is the single most misread table in nephrology. A result of 85 puts you in G2, and G2 on its own is not a disease — it is a normal finding in a great many healthy adults, particularly with age. Staging describes how much filtration capacity is present; calling it chronic kidney disease requires evidence of damage that has lasted three months or more.
- G5 (0–15)
- G4 (15–30)
- G3b (30–45)
- G3a (45–60)
- G2 (60–90)
- G1 (90–120)
| Category | Range |
|---|---|
| G5 | 0 to 15 mL/min/1.73m² |
| G4 | 15 to 30 mL/min/1.73m² |
| G3b | 30 to 45 mL/min/1.73m² |
| G3a | 45 to 60 mL/min/1.73m² |
| G2 | 60 to 90 mL/min/1.73m² |
| G1 | 90 to 120 mL/min/1.73m² |
Why race was removed from the equation
Until 2021, both the MDRD and CKD-EPI equations included a coefficient that multiplied the estimated GFR for Black patients — by around 1.16 in CKD-EPI, and 1.21 in MDRD. It came from an observation in the original development cohorts that Black participants had, on average, slightly higher serum creatinine at the same measured GFR. That average difference, most plausibly explained by differences in average muscle mass, was encoded as though race were a biological variable.
The practical consequence ran one way. A higher reported eGFR means a better-looking kidney function, which means later referral to a nephrologist, later diagnosis, and later placement on the transplant waiting list. In 2021 a joint task force of the National Kidney Foundation and the American Society of Nephrology recommended immediate adoption of a refit equation with race removed.2 Inker and colleagues published it the same year.1
This calculator has no race input
Not as an omission, but as the point. The 2021 equations were fitted without it and do not need it.
When creatinine misleads, and what to do about it
Creatinine is a proxy, and every proxy has conditions under which it fails. Because it originates in muscle, anything that changes muscle mass changes the estimate without changing kidney function at all.
- High muscle mass — bodybuilders and heavily trained athletes generate more creatinine, so eGFR reads low.
- Low muscle mass — older adults, people with muscle-wasting conditions, and amputees generate less, so eGFR reads high and can hide real impairment.
- Diet — a large meat meal or creatine supplementation raises serum creatinine for a day or more.
- Medications — trimethoprim and cimetidine block creatinine secretion in the tubules, raising the measured level without touching filtration.
- Acute illness — during acute kidney injury creatinine is not at steady state, and no eGFR equation is valid.
Cystatin C is produced by all nucleated cells rather than by muscle, so it fails under different conditions than creatinine does. KDIGO recommends confirming a creatinine-based estimate with cystatin C whenever the result would change what happens next — a diagnosis, a referral, or a drug dose.3 When this calculator has both, it leads with the combined equation, because that combination is more accurate than either marker alone.1
eGFR is not creatinine clearance
Cockcroft and Gault published a weight-based estimate of creatinine clearance in 1976, long before eGFR equations existed.4 It survives because a great many drug labels — including anticoagulants still in wide use — specify dose adjustments against it rather than against eGFR.
| eGFR (CKD-EPI 2021) | Cockcroft–Gault | |
|---|---|---|
| Units | mL/min/1.73m² | mL/min |
| Body size | Normalised to a standard body | Uses your actual weight |
| Built for | Staging kidney disease | Drug dosing |
| Inputs | Creatinine, age, sex | Creatinine, age, sex, weight |
Terms used on this page
- Glomerulus
- The filtering unit of the kidney — a tuft of capillaries where blood is first separated into filtrate and retained components. A healthy adult has around a million per kidney, and they are not replaced once lost.
- Albuminuria
- Albumin protein leaking into the urine, measured as the urine albumin-to-creatinine ratio. It is the second axis of KDIGO staging and is often the earlier sign of kidney damage — it can be raised while eGFR is still normal.
- Cystatin C
- A small protein produced at a constant rate by all nucleated cells and cleared by the kidneys. Because its production does not depend on muscle mass, it is the better marker in people whose muscle mass is unusual.
The formula
- Woman, 55 years, serum creatinine 0.9 mg/dL
- κ = 0.7, so Scr/κ = 1.286 — above 1, so the second term applies
- eGFR = 142 × 1 × 1.286^−1.200 × 0.9938^55 × 1.012
Source: CKD-EPI 2021 (race-free). Published clinical/scientific formula.
Limitations
- Not valid in acute kidney injury: the equations assume creatinine is at a steady state, and it is not while function is changing rapidly.
- Not valid in pregnancy, and not valid under 18 — children need a pediatric equation such as the Bedside Schwartz.
- Unreliable at the extremes of muscle mass: bodybuilders, amputees, people with muscle-wasting conditions, and anyone on a very high-meat or creatine-supplemented diet.
- Some medications (trimethoprim, cimetidine) raise serum creatinine without changing filtration at all.
- The result is normalised to 1.73 m². If your body surface area is far from that, drug dosing may need the un-normalised figure.
References
- 1.New creatinine- and cystatin C-based equations to estimate GFR without race. Inker et al., New England Journal of Medicine 385(19):1737–1749, 2021.
- 2.A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease. Delgado et al., American Journal of Kidney Diseases 79(2):268–288, 2022.
- 3.KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Disease: Improving Global Outcomes, Kidney International 105(4S), 2024.
- 4.Prediction of creatinine clearance from serum creatinine. Cockcroft & Gault, Nephron 16(1):31–41, 1976.
- 5.Chronic Kidney Disease Basics. Centers for Disease Control and Prevention, 2024.
Frequently asked questions
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