Glomerular Filtration Rate Calculator - eGFR from Creatinine

A glomerular filtration rate calculator takes a standardized serum creatinine value, the patient's age, and sex and returns an estimated GFR in mL/min/1.73 m2, the number clinicians use to summarize how well the kidneys are filtering blood. The result is the starting point for chronic kidney disease screening and medication dose adjustments.

• • CKD screening at a routine visit: Confirm a normal or slightly low eGFR from a recent blood test and translate it into the G1 to G5 stage label.
• • Tracking a known kidney condition: Re-enter a new creatinine value at the next blood draw and watch the eGFR change over time so the trend is visible before the next clinic visit.
• • Medication dose review: Bring a current eGFR into a pharmacist or prescriber conversation about renally cleared drugs such as metformin or apixaban.
• • Preparing questions for a referral: Use the stage label and the numeric result as a concrete prompt for questions about repeat testing or referral timing.

Creatinine rises when the kidneys filter less of it out, so an eGFR below the expected range usually points to a real change in kidney function rather than a single noisy lab result. The race-free CKD-EPI 2021 equation is the default in most US laboratories because the 2021 NKF/ASN Task Force concluded that the older race coefficient introduced a known bias. Read the result alongside the urine albumin-to-creatinine ratio, because eGFR alone can overstate kidney health when albuminuria is high.

For an alternative view of the same kidney-filtration question that uses a different layout and a 2009-era equation for cross-check, the GFR Calculator sits next to this tool in the health-fitness cluster.

The calculator implements the race-free CKD-EPI 2021 creatinine equation, the standard adult eGFR formula the National Kidney Foundation now recommends, and labels the result with the G1 to G5 cut points used for chronic kidney disease staging.

• SCr: Standardized serum creatinine in mg/dL from an IDMS-traceable lab assay.
• kappa: Sex-specific scaling factor: 0.7 for females, 0.9 for males.
• alpha: Sex-specific exponent: -0.241 for females, -0.302 for males.
• Age: Age in whole years, used for the 0.9938^Age decay factor.
• 1.012: Female-only multiplier that captures the average sex difference in creatinine production.

The min(ratio, 1) and max(ratio, 1) terms keep the formula stable no matter how low or high the creatinine is, which is why the calculator can return eGFRs well above 120 for young patients and well below 15 for patients in kidney failure.

According to National Kidney Foundation CKD-EPI Creatinine Equation 2021, the CKD-EPI 2021 creatinine equation is expressed as 142 x min(SCr/kappa, 1)^alpha x max(SCr/kappa, 1)^-1.200 x 0.9938^Age x 1.012 if female, and it is the equation the NKF/ASN Task Force now recommends over the older race-adjusted 2009 form.

When a low eGFR comes with a metabolic acidosis story, the Anion Gap Calculator is the natural next tool to run on the same venous blood gas to see whether the kidney is also losing its acid-base work.

These four concepts are the ones a patient or a non-nephrology clinician will run into most often when reading the number the calculator returns.

Read these concepts together rather than separately, because a single eGFR number can mean very different things at different ages. The eGFR result is most useful when it is compared with the patient's own previous result.

Because creatinine production scales with muscle mass, the BMI Calculator gives the context the eGFR does not have when the creatinine looks low or high for a body size that is not what the lab average assumes.

Work through these steps every time you sit down with a new creatinine value, so the result is consistent with the way the lab or the nephrologist would compute it.

1. 1 Pick the sex and enter the age: Choose the patient's sex, then type their age in whole years. The 2021 equation is only validated for adults 18 and older.
2. 2 Enter the standardized serum creatinine: Type the standardized serum creatinine from the lab report in mg/dL. If the lab reports umol/L, divide by 88.4 first.
3. 3 Read the eGFR in the primary result box: Watch the numeric eGFR in the primary result box. The value updates as soon as any input changes.
4. 4 Read the CKD stage label: Below the numeric result, read the CKD G1 to G5 stage label, which uses the National Kidney Foundation cut points.
5. 5 Compare with a prior result: Bring the new eGFR next to a previous one from the same lab and read the change. A drop of more than 5 mL/min/1.73 m2 in a year, or a drop that crosses a stage boundary, is usually the trigger for repeat testing or a referral.

A 65 year old woman has a routine blood test that reports a standardized serum creatinine of 1.0 mg/dL. The user picks Female, enters 65 in the age field, and types 1.0 in the serum creatinine field. The calculator returns 62.52 mL/min/1.73 m2 with the G2 mild loss label.

The sex-specific kappa and 1.012 female multiplier in the 2021 equation make the BMI Calculator for Women a useful sanity check whenever the patient and the lab disagree on the sex field, since a wrong sex flips the result by a clinically meaningful amount.

These benefits are most useful in the first conversation about a creatinine result, when the patient wants a single number that summarizes kidney function and the next step the team is likely to recommend.

• • Translates a creatinine result into a stage: Turns a raw serum creatinine number into an eGFR in mL/min/1.73 m2 and a G1 to G5 stage label.
• • Follows the current NKF/ASN guidance: Uses the race-free CKD-EPI 2021 equation, which the 2021 Task Force now recommends over the older race-adjusted 2009 form.
• • Helps with medication dose review: Surfaces a current eGFR quickly enough that a pharmacist or prescriber can use it as a starting point for renally cleared drugs such as metformin or apixaban.
• • Useful for tracking change over time: Returns a numeric eGFR, so the user can compare two results side by side and see whether kidney function is stable or trending down.
• • Clear disclaimer for pediatric cases: Returns a 'not for adults under 18' label when the age is below 18.

The calculator is a decision aid, not a diagnosis. The same number can mean different things in a young athlete and in a person who has lost a lot of muscle mass, so a clinician should always interpret the eGFR alongside the urine albumin-to-creatinine ratio and the trend over time.

A short-term drop in eGFR is sometimes just dehydration, so the Daily Water Intake Calculator helps the user see whether the patient's usual fluid intake is the kind of value that could plausibly explain a single low result.

These factors change the eGFR the calculator returns, and they are the same variables a clinician reviews whenever an eGFR value looks unexpectedly high or low.

• • The calculator returns a single number that summarizes kidney filtration, not a diagnosis. A persistently low eGFR still needs a urine albumin-to-creatinine ratio and a clinical exam before a CKD diagnosis is recorded.
• • The result is a screening estimate, not a measured GFR. The reference test is a measured GFR from an iohexol clearance study, reserved for cases where the eGFR is unreliable.

When the eGFR is below 15 mL/min/1.73 m2, the calculator returns the G5 kidney failure label and the team should move from 'is this real' to 'what is the next step', usually a nephrology visit or transplant evaluation.

According to National Kidney Foundation stages of chronic kidney disease, the CKD stages are G1 at 90 or above, G2 at 60 to 89, G3a at 45 to 59, G3b at 30 to 44, G4 at 15 to 29, and G5 below 15, and the same cut points are used by the eGFR calculator to label the result.

According to National Kidney Foundation KDOQI eGFR calculator guidance, the indexed eGFR in mL/min/1.73 m2 is the right unit for CKD staging and progression, while a body-surface-area adjusted eGFR in mL/min is preferred for medication-related decisions such as diabetes or oncology dosing.

Patients with a low eGFR and a history of stones benefit from the Kidney Stone Calculator alongside this tool, because recurrent stones are one of the reversible causes of a falling eGFR and the two tools cover the same kidney in different ways.