GFR Calculator

Related Calculators

Estimated GFR: An estimate of how well the kidneys filter blood, reported here in mL/min/1.73 m2.

G category: A kidney function range label from G1 to G5 based on Estimated GFR.

Serum creatinine (mg/dL): A blood test used in all pathways on this page.

Cystatin C (mg/L): Another blood test that can be combined with creatinine in the adult combined pathway.

Deindexed eGFR: An optional body-size-adjusted estimate in mL/min instead of mL/min/1.73 m2.

Estimated body surface area: A size estimate from height and weight that is used to calculate Deindexed eGFR.

Equation pathway: The formula set chosen for an adult creatinine-only result, an adult creatinine plus cystatin C result, or a child bedside CKiD result.

Mistake: Using an adult option in Equation pathway for someone younger than 18.
Fix: Switch Equation pathway to the child option when Age (years) is 1 to 16.

Mistake: Leaving Cystatin C (mg/L) blank when the adult creatinine + cystatin C pathway is selected.
Fix: Enter the lab value in Cystatin C (mg/L), or change Equation pathway to the adult creatinine-only option.

Mistake: Entering Serum creatinine (mg/dL) in umol/L without changing Creatinine input unit.
Fix: Set Creatinine input unit to the unit printed on the report before you calculate.

Mistake: Forgetting that Height (cm) is required for the child pathway and for Estimated body surface area when you want Deindexed eGFR.
Fix: Enter Height (cm), and if you used inches, change Height input unit first.

Mistake: Expecting Deindexed eGFR to appear when Weight (kg) is missing.
Fix: Select "Show body-size-adjusted eGFR", then add both "Height (cm)" and "Weight (kg)" with matching units so the calculator can estimate body surface area.

Mistake: Treating one low Estimated GFR result as a CKD diagnosis.
Fix: Read Interpretation and Important note together, and use Known abnormal kidney findings for 3 months or longer to add chronicity context.

• These results are estimates of GFR, not direct measured GFR.
• Adult equations here are only for age 18 years or older, and the bedside CKiD pathway is only for ages 1 to 16 years.
• A single Estimated GFR result does not diagnose chronic kidney disease by itself; persistence over at least 3 months and other kidney findings matter.
• Results may be less reliable when kidney function is changing quickly, during pregnancy, or when muscle mass is very unusual.
• Deindexed eGFR and Estimated body surface area are shown only when valid height and weight are provided.
• Body surface area is estimated with the Mosteller formula, so the deindexed value is still an estimate.
• The calculator follows the selected input units and converts them before applying the equation.

How the calculator chooses the formula

The selected Equation pathway determines which equation is used. Adult pathways use the 2021 race-free CKD-EPI equations, and the child pathway uses the bedside CKiD equation.[1][2]

Formulas used

Adult creatinine only: eGFR = 142 x min(SCr/k,1)^a x max(SCr/k,1)^-1.200 x 0.9938^Age x sex factor

Adult creatinine + cystatin C: eGFR = 135 x min(SCr/k,1)^a x max(SCr/k,1)^-0.544 x min(Scys/0.8,1)^-0.323 x max(Scys/0.8,1)^-0.778 x 0.9961^Age x sex factor

Child bedside CKiD: eGFR = 0.413 x Height_cm / SCr

BSA = sqrt((Height_cm x Weight_kg) / 3600)

Deindexed eGFR = indexed eGFR x (BSA / 1.73)

G1 if eGFR >= 90; G2 if 60 to 89; G3a if 45 to 59; G3b if 30 to 44; G4 if 15 to 29; G5 if less than 15

Variable meaning

SCr means serum creatinine in mg/dL. Scys means cystatin C in mg/L. In the adult equations, k and the exponent a depend on Sex. The calculator converts creatinine from umol/L to mg/dL by dividing by 88.4 before using the formula.

Worked mini-example

Example: adult creatinine-only pathway, female, Age (years) 50, Serum creatinine (mg/dL) 1.0. The calculator uses the adult 2021 CKD-EPI creatinine equation and gives an Estimated GFR of about 72.5 mL/min/1.73 m2, which falls in G category G2.

How interpretation is assigned

The page maps the indexed eGFR to a KDIGO G category and then gives a short plain-language Interpretation. If Known abnormal kidney findings for 3 months or longer is set to No, the note explains that chronicity is not established, because eGFR range alone does not diagnose CKD.[3][4]

Assumptions behind the result

The result assumes the lab values are correct, the selected pathway matches the person's age, and kidney function is reasonably stable at the time of testing. Deindexed eGFR is shown only when valid height and weight are available, because it depends on estimated body surface area rather than the standard 1.73 m2 indexing area.