🫘 eGFR Kidney Age Calculator
Your lab report lists an eGFR number. This tool converts that number into something more intuitive: the age of an average healthy person whose kidneys filter at the same rate as yours.
📖 How the Kidney Age Estimate Works
The calculator first computes your estimated glomerular filtration rate (eGFR) with the CKD-EPI 2021 creatinine equation — the race-free formula now recommended by the NKF-ASN Task Force and used by most US labs. eGFR expresses how many millilitres of blood your kidneys clean per minute, normalised to a standard body surface area of 1.73 m².
Healthy kidneys filter best in your twenties and then decline slowly. A typical adult loses roughly 0.8–1 mL/min per year after about age 30–40, which is why a 70-year-old with an eGFR of 70 is completely normal while a 30-year-old with the same number would warrant a conversation with a doctor.
To turn that into a "kidney age", the tool inverts the equation: it searches for the age at which an average healthy person of your sex would produce exactly your eGFR. If your eGFR is 95 at age 62, your kidney age comes out well below 62 — your filtration is that of a younger adult. If your eGFR is 55 at age 45, your kidney age lands above your real age, which is the signal worth discussing with a clinician.
This is an educational estimate, not a diagnosis. eGFR is affected by muscle mass, hydration, recent protein intake, pregnancy, and certain medications. Bodybuilders and people with amputations can have misleadingly high creatinine; frail elderly people can have misleadingly low creatinine that flatters their eGFR. Always interpret a lab value with the clinician who ordered it.
📉 eGFR Stages vs. Age (KDIGO)
| eGFR (mL/min/1.73m²) | KDIGO Stage | What it usually means | Typical age where this is common |
|---|---|---|---|
| 90 and above | G1 | Normal filtration (with kidney damage markers it becomes G1A) | Any adult; most common under 40 |
| 60 – 89 | G2 | Mildly reduced; normal for older adults | 50s and up, increasingly common |
| 45 – 59 | G3a | Mild to moderate reduction | Common in the 60s–70s |
| 30 – 44 | G3b | Moderate to severe reduction | 70s–80s; earlier if diabetic or hypertensive |
| 15 – 29 | G4 | Severely reduced — nephrology referral indicated | Usually 75+; earlier with disease |
| Below 15 | G5 | Kidney failure range; dialysis or transplant evaluation | Rare without known disease |
Staging is only valid after two readings at least 90 days apart, because acute illness can temporarily drop eGFR by 20 points or more.
💡 Who This Calculator Is For
🧾 Reading your annual bloodwork
If your physical came back with an eGFR of 78 and you are 41, this tells you how that number compares to a healthy 41-year-old rather than leaving you to guess whether 78 is "good".
📉 Tracking a trend over years
A single eGFR means little on its own. Running the same number through this tool each year shows whether your kidney age is climbing faster than your real age — the pattern doctors actually care about.
🩸 Living with diabetes or hypertension
Both conditions are the leading causes of chronic kidney disease. Patients monitoring eGFR twice a year can use kidney age as a plain-language way to see whether control is working.
💊 Checking medication impact
NSAIDs, lithium, some antibiotics and contrast dye can depress eGFR. Comparing kidney age before and after a course of treatment gives a quick sense of the magnitude.