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GFR Calculator

Estimate glomerular filtration rate using CKD-EPI 2021, MDRD, and Cockcroft-Gault formulas. Includes pediatric Schwartz formula.

GFR for Adults

For people aged 18 and older. Results from 3 formulas.

GFR for Children

For people aged 18 or younger. Uses the Bedside Schwartz formula.

What is Glomerular Filtration Rate?

GFR measures how much blood your kidneys filter per minute, expressed in mL/min/1.73m² (normalized to body surface area). It is the primary indicator of kidney function and is used to diagnose and stage chronic kidney disease (CKD).

GFR Formulas

CKD-EPI 2021 (Recommended)

The current standard from KDIGO guidelines. This race-free equation was adopted after the 2021 NKF-ASN task force recommendation:

eGFR = 142 × min(SCr/κ, 1)α × max(SCr/κ, 1)−1.200 × 0.9938Age × (1.012 if female)

Where κ = 0.7 (female) or 0.9 (male), and α = −0.241 (female) or −0.302 (male).

MDRD (Modification of Diet in Renal Disease)

The 4-variable MDRD formula is less accurate above 60 mL/min but still widely used:

eGFR = 175 × SCr−1.154 × Age−0.203 × (0.742 if female)

Cockcroft-Gault

The oldest formula, still used for drug dosing. Requires body weight and is not normalized to body surface area:

CrCl = ((140 − Age) × Weight) / (72 × SCr) × (0.85 if female)

Bedside Schwartz (Pediatric)

For children under 18:

eGFR = 0.413 × Height(cm) / SCr

CKD Stages

StageGFR (mL/min/1.73m²)Description
G1≥ 90Normal or high function
G260–89Mildly decreased
G3a45–59Mild to moderate decrease
G3b30–44Moderate to severe decrease
G415–29Severely decreased
G5< 15Kidney failure (dialysis or transplant may be needed)

Factors Affecting GFR

  • Age: GFR naturally declines about 1 mL/min/year after age 30
  • Diet: High protein intake temporarily increases GFR; creatine supplements raise serum creatinine without kidney damage
  • Muscle mass: Muscular individuals may have higher creatinine, underestimating GFR
  • Medications: NSAIDs, ACE inhibitors, and some antibiotics can affect GFR
  • Hydration: Dehydration temporarily lowers GFR

When to See a Doctor

This calculator provides estimates only and should not replace medical advice. See a healthcare provider if your estimated GFR is below 60, or if you have symptoms like persistent fatigue, swelling, changes in urination, or foamy urine.

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Frequently Asked Questions

What is GFR?

Glomerular filtration rate (GFR) measures how well your kidneys filter blood. It estimates how many milliliters of blood the glomeruli filter per minute. Normal GFR is around 90-120 mL/min/1.73m².

What is serum creatinine?

Creatinine is a waste product from normal muscle metabolism. Kidneys filter it from blood. When kidneys are damaged, creatinine builds up, so higher levels suggest lower kidney function.

Which formula is most accurate?

The CKD-EPI 2021 equation is the current standard recommended by KDIGO guidelines. It replaced the race-based CKD-EPI 2009. MDRD is less accurate at higher GFR values. Cockcroft-Gault is older but still used for drug dosing.

Why is race not included?

This calculator uses the 2021 CKD-EPI equation, which removed the race coefficient. NKF and ASN recommended this change in 2021 to reduce health disparities.

What GFR indicates kidney disease?

GFR below 60 mL/min for 3+ months indicates chronic kidney disease (CKD). However, even GFR 60-89 with other kidney damage markers (proteinuria) may qualify as CKD stage G2.

Can GFR improve after diagnosis?

GFR can improve if kidney damage is caught early and the underlying cause is treated, such as controlling blood pressure or blood sugar in diabetic nephropathy. Advanced or end-stage kidney disease does not significantly recover.

Worked example: what does a creatinine of 1.1 mg/dL mean for a 55-year-old woman?

Using CKD-EPI 2021, a 55-year-old woman with serum creatinine 1.1 mg/dL has an estimated GFR of roughly 57 mL/min/1.73m², placing her in CKD stage G3a. This is a screening estimate — a clinician should interpret lab-reported eGFR in full clinical context.

What besides kidney disease can raise serum creatinine?

High muscle mass, large dietary meat intake, and certain medications (such as trimethoprim or cimetidine) can raise creatinine without true kidney impairment. Conversely, low muscle mass in elderly or malnourished patients can keep creatinine falsely low and mask reduced kidney function.