GFR Calculator

The Glomerular Filtration Rate (GFR) is the key measure of kidney function. This calculator estimates your eGFR from a standard blood creatinine test — helping you understand what stage of kidney function you're in.

How to Use This Calculator

1. Enter your serum creatinine level (from a blood test, in mg/dL or μmol/L).
2. Enter your age.
3. Select your gender.
4. Click Calculate to see your estimated GFR (eGFR) in mL/min/1.73m².

CKD-EPI Formula (2021)

The 2021 CKD-EPI Creatinine equation (race-free) is currently the recommended standard:

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(−1.200) × 0.9938^Age

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

This is complex — use the calculator above for instant results.

GFR Stages of Kidney Disease

• G1: eGFR ≥ 90: Normal or high (with kidney damage markers)
• G2: eGFR 60–89: Mildly decreased
• G3a: eGFR 45–59: Mildly to moderately decreased
• G3b: eGFR 30–44: Moderately to severely decreased
• G4: eGFR 15–29: Severely decreased — prepare for kidney replacement therapy
• G5: eGFR < 15: Kidney failure — dialysis or transplant needed

Common Mistakes to Avoid

• Using GFR calculator without a recent creatinine test — This calculator requires actual lab values. Don't estimate creatinine from symptoms.
• Ignoring trends over time — A single eGFR reading is less informative than the trend over months/years. A stable eGFR of 55 is less concerning than one that dropped from 75 to 55 over six months.
• Assuming low eGFR always means CKD — Temporary drops occur with dehydration, medications (NSAIDs, contrast dye), and illness. Persistent low eGFR (>3 months) indicates CKD.

Frequently Asked Questions

What is a normal GFR for my age?

eGFR naturally declines with age. Approximate normal values: 30s: 100+, 40s: 90+, 50s: 80+, 60s: 70+, 70+: 60+. However, any eGFR below 60 is generally concerning regardless of age.

Can I improve my GFR?

For early stages (G1–G2), lifestyle modifications can preserve kidney function: controlling blood pressure and blood sugar, avoiding NSAIDs, staying hydrated, and not smoking. In advanced CKD, the focus shifts to slowing decline.

Should I see a nephrologist?

Referral is typically recommended when eGFR < 30 (G4), or earlier if eGFR is declining rapidly, there is significant proteinuria, or the cause of CKD is uncertain. Discuss your specific values with your primary care provider.

Conclusion

eGFR is a critical kidney health indicator. Use this calculator to understand your lab results — and always discuss them with your healthcare provider, who can interpret them in the context of your full clinical picture.

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