GFR Calculator
Turn a creatinine result into an eGFR and a CKD stage, using the 2021 race-free equation.
https://calculators.nirajiitr.com/health/gfr-calculator
How it works
The equation bends at a creatinine threshold that differs by sex, which is what the two halves do: below the threshold one exponent applies, above it another and steeper one, so filtration falls away quickly once creatinine climbs. Creatinine is a waste product of muscle, produced at a fairly steady rate and cleared almost entirely by the kidneys — so the more of it sitting in the blood, the less the kidneys are clearing. The result is normalised to a body surface area of 1.73 square metres so that readings compare between people of different sizes.
eGFR = 142 x min(Scr/K, 1)^a x max(Scr/K, 1)^-1.200 x 0.9938^age x 1.012 [if female]- Scr
- Serum creatinine in mg/dL
- K
- 0.7 for females, 0.9 for males
- a
- -0.241 for females, -0.302 for males
- 0.9938^age
- The steady decline in filtration with age
- eGFR
- Estimated filtration in mL/min/1.73m2
Worked example
A 55-year-old woman with a serum creatinine of 1.1 mg/dL.
- 1K is 0.7 for a female, so the ratio Scr/K is 1.1 / 0.7 = 1.571
- 2The ratio is above 1, so the steep exponent applies: 1.571^-1.200 = 0.581
- 3Apply the age term: 0.9938^55 = 0.710
- 4Multiply through: 142 x 0.581 x 0.710 x 1.012 (female) = 59.3
An eGFR of about 59 — stage G3a, mildly to moderately reduced, and worth repeating to confirm it is sustained rather than a one-off.
Frequently asked questions
What is a normal GFR?
Above 90 mL/min/1.73m2 is considered normal, though filtration declines naturally with age and a healthy person in their seventies may sit in the 60s without anything being wrong. That is why stage G2, between 60 and 89, is not classed as kidney disease on its own: it needs an accompanying marker of damage, most often protein in the urine, before it counts as chronic kidney disease.
Why did the equation stop using race?
Older versions of CKD-EPI applied a coefficient that raised the reported eGFR for Black patients, on the basis of average differences in creatinine levels observed in study populations. In practice that meant a higher number from the same blood sample, and so later referral for specialist care and transplant assessment. A joint NKF and ASN task force recommended removing it, and the 2021 equation used here does not include race at all.
What is the difference between eGFR and creatinine clearance?
Creatinine clearance is measured, usually from a 24-hour urine collection, and slightly overestimates true filtration because the kidneys secrete a little creatinine as well as filtering it. eGFR is estimated from a single blood draw using an equation like this one. eGFR is far easier to obtain and is what most labs now report automatically, but a measured clearance is sometimes still used when the estimate is likely to be unreliable.
Can my eGFR be wrong?
It can be misleading in several common situations. Very muscular people produce more creatinine and so appear to have worse kidney function than they do; people with low muscle mass, including many older and chronically ill patients, appear to have better. A large meat meal, intense exercise, dehydration, pregnancy and some drugs including trimethoprim and cimetidine all shift the number without the kidneys changing at all. Cystatin C is sometimes used instead when the creatinine estimate is in doubt.
Should I use mg/dL or umol/L?
Use whichever your lab reported, and set the units here to match. US labs almost always report creatinine in mg/dL; most of the rest of the world uses umol/L. The conversion is a straight division by 88.4, which this calculator does for you, so a result of 97 umol/L is 1.1 mg/dL and gives an identical eGFR either way.
Does one low reading mean I have kidney disease?
No. Chronic kidney disease requires the reduction to be sustained for at least three months, which is precisely why a single result is not a diagnosis. A one-off low eGFR can reflect dehydration or an acute illness and may recover completely. The usual next step is a repeat test along with a urine albumin-to-creatinine ratio, which together give a far better picture than filtration alone.