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GFR Calculator

Estimate kidney function using clinically recognized GFR formulas for adults and children.

Last updated: 2026-05-15

Normal adult range: 0.6–1.2 mg/dL (53–106 µmol/L)

years

Used for creatinine threshold in the CKD-EPI 2021 formula. No race adjustment is applied.

What is GFR?

GFR (Glomerular Filtration Rate) is the volume of fluid filtered by the kidney’s glomeruli per unit of time, expressed as mL/min/1.73m² (normalized to body surface area). It is the single most important indicator of overall kidney function.

Because direct GFR measurement requires complex isotope testing, clinicians use serum creatinine — a waste product of muscle metabolism — to estimate GFR (eGFR). Creatinine is produced at a relatively constant rate by muscles and filtered by the kidneys; when kidneys fail, creatinine accumulates in the blood and eGFR falls.

The 2021 CKD-EPI equation (Chronic Kidney Disease Epidemiology Collaboration) is the current clinical standard, endorsed by KDIGO, NKF, and ASN. Unlike the older 2009 equation, it does not include a race coefficient, which was removed in 2021 to eliminate diagnostic inequity.

Why is GFR Important?

GFR is used to classify the severity of chronic kidney disease (CKD) into five stages (G1–G5) and guides clinical decisions:

  • Drug dosing: Many medications (metformin, antibiotics, anticoagulants) require dose adjustment or avoidance at GFR below 30–45 mL/min.
  • Contrast imaging: Iodinated contrast (CT scans) is restricted for GFR below 30 due to contrast-induced nephropathy risk.
  • Cardiovascular risk: CKD doubles the risk of cardiovascular events. Early detection of low GFR guides aggressive CV risk factor management.
  • Transplant planning: Referral to nephrology for dialysis or transplant evaluation typically begins at GFR < 20.
  • Dietary management: Protein, potassium, phosphorus, and sodium restrictions are titrated to GFR stage.

What Affects Creatinine (and eGFR Accuracy)?

Muscle mass

High muscle mass → higher creatinine → lower eGFR (may underestimate true GFR).

Diet

High red-meat intake transiently raises creatinine. Vegan/low-protein diets lower it.

Age

Muscle mass decreases with age, reducing creatinine generation and masking true GFR decline.

Hydration

Dehydration concentrates blood, raising creatinine and lowering calculated eGFR.

Medications

Cimetidine, trimethoprim, and creatine supplements block tubular secretion, raising creatinine without affecting true GFR.

Acute illness

Infections, surgery, or trauma can acutely raise creatinine independent of chronic kidney disease.

CKD Stage Classification (KDIGO 2024)

StageeGFRDescriptionAction
G1≥ 90NormalMaintain a healthy lifestyle, stay well-hydrated, and have routine check-ups if …
G260–89Mildly DecreasedMonitor blood pressure and blood glucose. Reduce sodium and processed foods. Fol…
G3a45–59Mild–ModerateConsult a primary care physician. Manage blood pressure (target <130/80 mmHg), a…
G3b30–44Moderate–SevereNephrology referral is recommended. Discuss protein restriction, phosphorus and …
G415–29Severely DecreasedUrgent nephrology consultation needed. Plan for renal replacement therapy (dialy…
G50–14Kidney FailureImmediate nephrology management required. Dialysis or kidney transplant evaluati…

How to Improve (or Protect) Kidney Health

Control blood pressure

Target < 130/80 mmHg. ACE inhibitors and ARBs are kidney-protective first-line agents.

Manage blood sugar

HbA1c < 7% in diabetes. SGLT2 inhibitors (empagliflozin) slow CKD progression.

Avoid NSAIDs

Regular ibuprofen/naproxen use reduces renal blood flow. Use acetaminophen instead.

Stay hydrated

6–8 glasses of water daily helps kidneys flush waste. More in hot climates or exercise.

Limit sodium

< 2.3 g/day (1 teaspoon of salt). Reduce processed foods, canned soups, and fast food.

Don't smoke

Smoking reduces kidney blood flow and doubles CKD progression risk.

Maintain healthy weight

Obesity increases risk of hypertension, diabetes, and CKD. Even 5–10% weight loss helps.

Annual kidney tests

If you have diabetes, hypertension, or family history of kidney disease — test annually.

Methodology & Formula Details

CKD-EPI 2021 (Race-free) — Adults

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

κ = 0.7 (female), 0.9 (male). α = −0.241 (female), −0.302 (male). Source: Inker et al., NEJM 2021.

MDRD 4-variable (IDMS-traceable) — Adults

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

Source: Levey et al., Ann Intern Med 2006.

Mayo Quadratic — Adults

eGFR = exp(1.911 + 5.249/SCr − 2.114/SCr² − 0.00509×age − [0.2 if female])

SCr floor of 0.8 mg/dL applied per original paper. Source: Rule et al., JASN 2004.

Bedside Schwartz — Children

eGFR = (0.413 × Height in cm) ÷ Serum Creatinine (mg/dL)

Validated for children aged 1–16. Source: Schwartz & Arbelaez, CKJ 2012.

Frequently Asked Questions

A GFR of 90 mL/min/1.73m² or higher is considered normal (G1). Values of 60–89 (G2) may be normal in older adults but should be monitored. Below 60 for more than 3 months indicates chronic kidney disease.

eGFR stands for Estimated Glomerular Filtration Rate. It is calculated from a blood test (serum creatinine), your age, and sex using validated equations like CKD-EPI 2021. It estimates how well your kidneys are filtering blood per minute per 1.73 m² body surface area.

Yes. Dehydration reduces blood flow to the kidneys, temporarily lowering GFR and raising serum creatinine. For accurate results, be normally hydrated and avoid extreme exercise or high-protein meals in the 24 hours before your blood test.

Not always. Factors like dehydration, very high muscle mass (or low muscle mass in frail elderly), a high-meat diet, certain medications, or acute illness can transiently affect creatinine. CKD requires a sustained GFR below the threshold for at least 3 months, confirmed on two separate tests.

Serum creatinine above 2.0 mg/dL in women or 2.5 mg/dL in men generally indicates significantly reduced kidney function (roughly GFR < 30). Values above 4.0 mg/dL may indicate severe kidney disease or failure. However, normal ranges vary by laboratory and method.

Yes. GFR naturally declines with age — approximately 0.5–1 mL/min/1.73m² per year after age 40. A GFR of 75 in a healthy 70-year-old is often considered normal, whereas the same value in a 30-year-old warrants investigation.

The 2021 CKD-EPI equation removed the race coefficient at the recommendation of the National Kidney Foundation (NKF) and American Society of Nephrology (ASN). The prior 2009 formula added a multiplier for Black patients, which was shown to cause diagnostic inequities. The 2021 race-free version performs equally well across populations.

Both estimate GFR from serum creatinine, age, and sex. CKD-EPI 2021 is more accurate across the full GFR range (particularly above 60 mL/min) and is the current clinical standard. MDRD tends to underestimate GFR when it is above 60, which can lead to over-diagnosis of CKD in patients with mild reduction.

It can. Treating reversible causes (dehydration, urinary obstruction, infections, nephrotoxic drugs) can restore GFR. In CKD, slowing progression is the main goal. Tight blood pressure and blood sugar control, ACE inhibitors/ARBs, SGLT2 inhibitors, and dietary changes can meaningfully preserve remaining kidney function.

Children are assessed using the Bedside Schwartz formula: eGFR = (0.413 × Height in cm) ÷ Serum Creatinine in mg/dL. This accounts for the fact that creatinine production is proportional to muscle mass, which scales with body size in growing children.

Stage 3 CKD is split into G3a (GFR 45–59 — mildly to moderately decreased) and G3b (GFR 30–44 — moderately to severely decreased). Many people in Stage 3 have no symptoms. Regular nephrology follow-up, medication review, and dietary management are important at this stage.

Yes. Eating a large amount of protein (especially red meat) before the test can transiently raise creatinine and lower calculated eGFR. Cooked red meat releases creatinine from creatine during cooking. Fasting from meat for 12 hours before a kidney test improves accuracy.

NSAIDs (ibuprofen, naproxen, diclofenac), certain antibiotics (aminoglycosides, vancomycin), contrast dyes used in CT/MRI scans, lithium, cyclosporine, and some blood pressure medications (at very high doses) can be nephrotoxic. Always inform your doctor about all medications before any procedure.

Average GFR by age group: 20–29 years → ~116 mL/min/1.73m²; 30–39 → ~107; 40–49 → ~99; 50–59 → ~93; 60–69 → ~85; 70–79 → ~75; 80+ → ~65. A GFR 30% below the average for age warrants investigation.

Stay well-hydrated (6–8 glasses water/day), maintain healthy blood pressure and blood sugar, limit sodium to < 2.3 g/day, avoid NSAIDs for routine pain relief, do not smoke, maintain healthy body weight, get regular aerobic exercise, and have annual kidney function tests if you are at risk (diabetes, hypertension, family history).

Scientific References

  1. Inker LA, et al. "New Creatinine– and Cystatin C–Based Equations to Estimate GFR without Race." N Engl J Med. 2021;385:1737–1749.
  2. Levey AS, et al. "Using Standardized Serum Creatinine Values in the Modification of Diet in Renal Disease Study Equation for Estimating GFR." Ann Intern Med. 2006;145:247–254.
  3. Rule AD, et al. "Using Serum Creatinine to Estimate GFR: Accuracy in Good Health and in Chronic Kidney Disease." Ann Intern Med. 2004;141:929–937.
  4. Schwartz GJ, Arbelaez AM. "Measuring GFR and Creatinine in Pediatric Patients." Clin J Am Soc Nephrol. 2012.
  5. KDIGO. "2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease." Kidney International Supplements, 2024.
  6. National Kidney Foundation. "Frequently Asked Questions about GFR Estimates." 2022.

Medical Disclaimer

This GFR calculator provides an estimated value for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Estimated GFR values can be affected by many clinical factors not captured in this tool. Never disregard professional medical advice or delay seeking it because of something you have read or calculated here. Always consult a qualified physician or nephrologist for kidney-related concerns.

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