eGFR Calculator

What This Tool Does

This calculator estimates Glomerular Filtration Rate (eGFR) — the primary measure of kidney function — using serum creatinine, serum cystatin C, or both. Enter the biomarker values along with age and sex, and the tool returns an estimated GFR in mL/min/1.73m², along with CKD classification, risk of progression, and recommended monitoring frequency. Both creatinine and cystatin C are not required — the calculator returns results based on whichever value or values you enter.

This tool is intended for use by healthcare professionals. Patients with questions about their kidney function should discuss results with their doctor or nephrologist.

You can also use this Poshan Calculator.

How It's Calculated

eGFR is not measured directly — it is estimated from blood biomarker levels using validated equations. The equations used in this calculator are the race-free CKD-EPI 2021 versions, recommended by the joint National Kidney Foundation and American Society of Nephrology Task Force.

CKD-EPI Creatinine Equation (2021)

The most widely used equation. It uses serum creatinine, age, and sex to estimate GFR. The 2021 version removes race as a variable, addressing concerns that the earlier 2009 equation produced systematically different estimates for Black patients in ways that were not physiologically justified.

CKD-EPI Creatinine-Cystatin C Equation (2021)

Combines both serum creatinine and serum cystatin C. This combined equation is generally more accurate than either biomarker alone, particularly in populations where creatinine-based estimates are less reliable — such as patients with extremes of muscle mass, amputees, or those on a high-protein diet.

CKD-EPI Cystatin C Equation (2012)

Uses serum cystatin C alone. Cystatin C is produced at a constant rate by all nucleated cells and is less affected by muscle mass, diet, or exercise than creatinine, making it a useful independent check — particularly in elderly patients, patients with cirrhosis, or those with sarcopenia.

Worked Example:

• Serum creatinine: 1.2 mg/dL
• Age: 55
• Sex: Female

Using the CKD-EPI creatinine equation (2021), this returns an eGFR of approximately 53 mL/min/1.73m² — placing this patient in GFR category G3a (mildly to moderately decreased kidney function).

Understanding eGFR Results — CKD Classification

GFR results are grouped into categories that guide clinical decision-making:

GFR category alone does not confirm CKD. For a CKD diagnosis, either an eGFR below 60 or evidence of kidney damage (such as albuminuria ≥30 mg/g) must be present for at least 3 months.

Albuminuria Category and CKD Risk

eGFR and albuminuria together determine CKD classification and risk of progression more accurately than either measure alone. The urine albumin-to-creatinine ratio (uACR) is categorised as:

A patient with an eGFR of 65 (G2) and a uACR above 300 mg/g (A3) carries a high risk of CKD progression — whereas a patient with an eGFR of 55 (G3a) and a uACR below 30 mg/g (A1) carries a lower risk. The combined GFR-ACR grid is the standard framework for communicating CKD prognosis.

Body Surface Area Adjustment

For medication dosing decisions — particularly chemotherapy, certain antibiotics, or renally cleared drugs — eGFR can be adjusted for body surface area using the Dubois Method. This produces an absolute GFR value in mL/min rather than the indexed value of mL/min/1.73m², which may be more appropriate for patients who deviate significantly from average body size. The calculator supports this adjustment when height and weight are entered.

Edge Cases and Special Rules

Paediatric patients: The CKD-EPI equations are validated for adults aged 18 and above. For patients under 18, use a dedicated paediatric eGFR calculator — the Schwartz or revised Schwartz equation is typically used for children.

Assay standardisation: The CKD-EPI equations assume creatinine is measured using a standardised assay traceable to isotope dilution mass spectrometry (IDMS). If your laboratory uses a non-standardised assay, results may differ. Indicate assay standardisation status in the calculator settings for appropriate handling.

Extremes of muscle mass: Creatinine is a byproduct of muscle metabolism. Patients with very high muscle mass (bodybuilders, certain athletes) may have elevated creatinine that overestimates kidney impairment. Conversely, patients with very low muscle mass (elderly, malnourished, amputees) may have low creatinine that overestimates kidney function. In these cases, cystatin C or the combined equation is preferred.

Acute kidney injury: eGFR equations are designed for chronic, stable kidney function. In acute kidney injury, creatinine is rising or falling rapidly and does not reflect a steady state — eGFR estimates during AKI are unreliable and should not be used for CKD staging.

Pregnancy: GFR increases significantly during pregnancy. Standard eGFR equations are not validated for pregnant patients and will underestimate true GFR.

Very high eGFR values: An eGFR above 60 in the absence of other markers of kidney damage does not fulfil CKD criteria, even if the value is lower than expected for the patient's age. GFR naturally declines with age — an eGFR of 70 at age 80 may be entirely normal.

Who Uses This

• Nephrologists and general practitioners staging CKD, monitoring progression, and deciding referral timing
• Pharmacists calculating drug doses for renally cleared medications where eGFR determines safe dosing thresholds
• Hospital clinicians assessing kidney function before contrast administration, surgery, or nephrotoxic drug exposure
• Endocrinologists and diabetologists monitoring kidney complications in patients with diabetes
• Researchers and clinical trialists screening participants based on kidney function criteria

eGFR vs. Serum Creatinine Alone

Serum creatinine is widely reported in routine blood tests but is a poor standalone indicator of kidney function. The same creatinine value of 1.3 mg/dL means very different things in a 25-year-old male athlete and a 75-year-old woman — because creatinine production is tightly linked to muscle mass, which varies with age, sex, and body composition. eGFR corrects for these differences using age and sex, producing a far more clinically meaningful estimate of actual filtration capacity.

FAQ

What is a normal eGFR?

Normal GFR varies with age and body size. In young adults it is typically above 90 mL/min/1.73m². GFR naturally declines with age — values above 60 are generally considered adequate kidney function in the absence of other markers of damage.

What is the difference between GFR and eGFR?

True GFR requires infusion of a filtration marker such as inulin and timed urine collection — a process too complex for routine clinical use. eGFR is an estimate derived from blood biomarkers using validated equations. In clinical practice, eGFR is what is used in the vast majority of settings.

Why was race removed from the CKD-EPI 2021 equation?

The 2009 CKD-EPI equation included a race coefficient that produced systematically higher eGFR estimates for Black patients, based on an assumed difference in average muscle mass. The NKF/ASN Task Force concluded that race is a social category, not a biological one, and that using it in the equation was not justified and introduced inequities in care. The 2021 equation is race-free and is now the recommended standard.

When should cystatin C be used instead of creatinine?

Cystatin C is preferred when creatinine-based estimates are unreliable — in patients with very low or very high muscle mass, those on a high-protein or ketogenic diet, elderly patients, those with liver disease or muscle-wasting conditions, or when confirmation of a borderline creatinine-based result is needed.

At what eGFR should a patient be referred to a nephrologist?

General guidance suggests referral when eGFR falls below 30 (G4), when eGFR declines rapidly (more than 5 mL/min/1.73m² per year), or when there is significant albuminuria or diagnostic uncertainty. Referral thresholds may vary by clinical context and local guidelines.

A Note on Results

This calculator is a clinical support tool, not a substitute for clinical judgement. eGFR is an estimate with inherent variability — a single result should always be interpreted alongside the patient's clinical history, other laboratory findings, and trend over time. A single eGFR below 60 does not confirm CKD; the finding must persist for at least 3 months. For patient-specific management decisions, consult current clinical practice guidelines and involve a nephrologist where appropriate.