GFR Calculator

A GFR (Glomerular Filtration Rate) calculator estimates how well your kidneys are filtering blood. The result — eGFR, expressed in mL/min/1.73 m² — is one of the primary markers of kidney health used by the NHS, NICE, KDIGO, and the US National Kidney Foundation.

The formulas used in this tool

This calculator supports the two most widely used equations. CKD-EPI 2021 is the current international standard — the race-free version recommended by the National Kidney Foundation and by NICE.

• CKD-EPI 2021 (race-free) — the preferred formula since 2021. Uses serum creatinine, age, and sex. More accurate for eGFR above 60 than MDRD.
• MDRD (4-variable) — the older standard. Still seen in lab reports and clinical notes. Accurate for eGFR < 60 but tends to underestimate values > 60.

Interpreting your eGFR — CKD stages

Your result is staged using the international KDIGO classification:

• Stage 1: eGFR ≥ 90 — normal kidney function (requires other evidence of kidney damage for CKD diagnosis)
• Stage 2: eGFR 60–89 — mildly reduced; often normal for older adults
• Stage 3a: eGFR 45–59 — mild-moderate reduction
• Stage 3b: eGFR 30–44 — moderate-severe reduction
• Stage 4: eGFR 15–29 — severely reduced; specialist referral needed
• Stage 5: eGFR < 15 — kidney failure; dialysis or transplant considered

🇺🇸 US context

US labs uniformly report eGFR alongside serum creatinine. Since 2021, CMS and the National Kidney Foundation endorse the race-free CKD-EPI 2021. Medicare covers annual kidney function screening for patients with diabetes or hypertension.

🇬🇧 UK context

The NHS uses CKD-EPI 2021 via primary care biochemistry. NICE guideline NG203 recommends annual eGFR monitoring for anyone with diabetes, hypertension, cardiovascular disease, or a family history of kidney disease. GPs will typically repeat a low eGFR within 2 weeks before confirming CKD.

How to keep your kidneys healthy

• Control blood pressure — target < 130/80 in most adults with CKD.
• Manage HbA1c if you have diabetes.
• Avoid NSAIDs (ibuprofen, diclofenac) when kidney function is already reduced.
• Stay hydrated — but avoid excessive protein and salt intake.
• Don't smoke; smoking accelerates kidney decline.