eGFR calculator

KDIGO GFR categories

Categories are the KDIGO 2012 GFR stages. Two points matter: G1 and G2 do not meet the definition of chronic kidney disease in the absence of other evidence of kidney damage, and staging always pairs GFR with albuminuria, which this calculator does not include.

• G1, normal or high: 90 and above. Normal filtration. On its own this does not rule out kidney disease, since albuminuria can be present with a normal eGFR.
• G2, mildly decreased: 60 to 89. Common with age and not classed as chronic kidney disease without other evidence of damage. Worth a urine albumin to creatinine ratio to complete the picture.
• G3a, mildly to moderately decreased: 45 to 59. Meets the GFR criterion for chronic kidney disease if it persists for at least three months. A reason for a clinician to review medications and repeat testing.
• G3b, moderately to severely decreased: 30 to 44. Requires medical management. Drug dosing, contrast imaging and several supplement choices change at this level.
• G4, severely decreased: 15 to 29. Specialist nephrology care. Not a range in which elective wellness therapies are appropriate without renal input.
• G5, kidney failure: Under 15. Kidney failure. Immediate specialist care.

Which equation this uses, and why it changed

This calculator uses the 2021 CKD-EPI creatinine equation, which removed the race coefficient that earlier versions applied to Black patients. The joint task force of the National Kidney Foundation and the American Society of Nephrology recommended the change, and it is now the recommended equation for US laboratories.

The reason matters. The older equations raised the estimated GFR for Black patients by around 16 percent on the basis of race, which in practice delayed specialist referral and transplant eligibility for some patients. The 2021 refit uses only creatinine, age and sex.

If your lab report shows a different number than this page, check which equation it used. Reports still occasionally carry MDRD or the 2009 CKD-EPI equation, and the difference is not trivial in the 45 to 75 range where decisions get made.

• eGFR = 142 x min(Scr/k, 1)^a x max(Scr/k, 1)^-1.200 x 0.9938^age x 1.012 if female.
• k is 0.7 for women and 0.9 for men. a is -0.241 for women and -0.302 for men.
• Result is indexed to a body surface area of 1.73 square meters.
• Creatinine in µmol/L is converted at 88.4 µmol/L per mg/dL before calculating.

Why creatinine is an imperfect stand-in

Creatinine is a breakdown product of creatine in muscle, so how much you produce depends on how much muscle you have. A muscular person with excellent kidney function can have a creatinine that looks mildly elevated, and a frail person with little muscle can have a normal creatinine while filtering poorly.

Meat intake, creatine supplementation, hard exercise in the preceding day and dehydration all raise it. Cystatin C, which is not produced by muscle, is the alternative marker, and current guidance suggests confirming with cystatin C when a creatinine based eGFR near a decision threshold does not match the clinical picture.

This is why a single eGFR should never be read as a verdict. The trend across several draws, taken under similar conditions, tells you far more than any one value.

Where this fits in a longevity program

Kidney function is one of the quiet screening numbers. It rarely produces symptoms until function is well down, it is included on almost every basic panel, and it constrains what is safe to prescribe.

It also gates therapy decisions in a practical sense. Reduced filtration changes dosing for many medications, changes the risk calculus around contrast imaging and non-steroidal anti-inflammatories, and is a reason a provider may decline a therapy that would be fine at a normal eGFR.

We recommend kidney markers on any panel you choose to have drawn, and the prescribing provider reviews what is available before any therapy is approved, which is one of the reasons a consult comes before an order.

Where this number is misleading

• Estimated, not measured. Measured GFR requires a filtration marker study, and eGFR carries meaningful error in individuals even when it performs well across populations.
• Creatinine reflects muscle mass, so it overestimates impairment in very muscular people and underestimates it in people with low muscle mass.
• Creatine supplements, a large meat meal, hard training and dehydration in the day before the draw all move it.
• It is not valid in pregnancy, in acute kidney injury, or in people at extremes of body size, and it is not for children.
• GFR is only half of CKD staging. Albuminuria must be measured separately, and it can be abnormal while eGFR is normal.

Common questions

What is a normal eGFR?

90 or above is classed as normal or high by KDIGO, and 60 to 89 is described as mildly decreased, which is common with age and is not chronic kidney disease on its own. Values below 60 persisting for three months meet the GFR criterion for chronic kidney disease.

Why does my eGFR differ from my lab report?

Usually the equation. Labs have moved to the 2021 CKD-EPI equation at different times, and some reports still use MDRD or the 2009 equation with a race coefficient. Creatinine assay differences and rounding also contribute.

Does creatine supplementation affect eGFR?

It can raise serum creatinine without any change in kidney function, since creatinine is a breakdown product of creatine. If you supplement, tell whoever interprets the result, and consider a cystatin C based estimate if the number matters for a decision.

Why was race removed from the eGFR equation?

The older coefficient raised estimated GFR for Black patients on the basis of race alone, which delayed referral and transplant listing for some patients. The 2021 NKF-ASN task force recommended a refit using only creatinine, age and sex, which is the equation used here.

Sources and disclosures

• Inker LA, Eneanya ND, Coresh J, et al. New creatinine- and cystatin C-based equations to estimate GFR without race. New England Journal of Medicine, 2021
• Delgado C, Baweja M, Crews DC, et al. A unifying approach for GFR estimation: recommendations of the NKF-ASN Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease, 2021
• KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease, GFR and albuminuria categories
• National Kidney Foundation. CKD-EPI creatinine equation (2021)
• These calculators are for education. They do not diagnose, they do not replace testing, and they are not a prescription. Baseline is a wellness consultancy, and any prescription is written by an independent licensed provider in our network who has reviewed your history, your goals and any lab work you choose to share.