A normal eGFR for adults is generally above 90 mL/min/1.73 m², but that number shifts significantly with age. eGFR (estimated glomerular filtration rate) measures how well your kidneys filter waste from your blood. It’s calculated from a simple blood test and is the primary way doctors assess kidney function.
Normal eGFR by Age
Kidney function naturally declines as you get older, so what’s “normal” at 25 isn’t the same as what’s normal at 70. The National Kidney Foundation provides these average eGFR values for healthy adults:
- Ages 20–29: 116
- Ages 30–39: 107
- Ages 40–49: 99
- Ages 50–59: 93
- Ages 60–69: 85
- Ages 70+: 75
This means a 65-year-old with an eGFR of 82 is likely in perfectly normal territory, even though that number falls below the general 90 threshold. Context matters more than the raw number.
How Fast eGFR Drops Each Year
In healthy adults without high blood pressure, kidneys lose about 0.4 to 1.0 mL/min/1.73 m² of filtering capacity per year. That’s a slow, predictable decline and not a cause for concern on its own. High blood pressure accelerates the process considerably, with some studies showing losses as steep as 3.6 mL/min per year at higher eGFR levels. This is one reason blood pressure control is so important for long-term kidney health.
How eGFR Is Calculated
Your eGFR comes from a blood test that measures creatinine, a waste product your muscles produce at a fairly steady rate. A lab plugs your creatinine level, age, and sex into a standard formula called the CKD-EPI 2021 equation. The current version of this equation, updated in 2021, no longer includes race as a variable, which was a significant change from earlier versions.
There’s also a second version of the test that measures a different blood marker called cystatin C. This alternative tends to be more accurate in situations where creatinine-based eGFR can be misleading, particularly for people with diabetes, those in the high-normal kidney function range, or anyone whose muscle mass doesn’t reflect the average (more on that below).
What Can Skew Your Results
Because the standard eGFR equation relies on creatinine, anything that changes your creatinine levels for reasons unrelated to your kidneys can throw off the estimate. Creatinine is a byproduct of muscle metabolism, so people with unusually high or low muscle mass often get misleading results. Bodybuilders may appear to have worse kidney function than they actually do, while frail older adults or people with muscle-wasting conditions may appear healthier than they are.
Other situations where creatinine-based eGFR becomes less reliable include pregnancy, recent amputations, paraplegia, very low-protein or vegetarian diets, and acute illness requiring hospitalization. In these cases, a cystatin C-based test or a combined creatinine-cystatin C equation gives a clearer picture. If you fall into one of these categories and your eGFR result seems off, it’s worth asking about cystatin C testing.
What Low eGFR Numbers Mean
Chronic kidney disease is diagnosed when your eGFR stays below 60 for three months or longer. A single low reading doesn’t necessarily mean you have kidney disease, since dehydration, medications, or a temporary illness can cause a dip. The three-month threshold exists specifically to distinguish a true decline from a temporary fluctuation.
Kidney disease is grouped into stages based on eGFR:
- Stage 1 (eGFR 90+): Normal filtering, but other signs of kidney damage are present (like protein in the urine)
- Stage 2 (eGFR 60–89): Mildly reduced function
- Stage 3a (eGFR 45–59): Mild to moderate loss
- Stage 3b (eGFR 30–44): Moderate to severe loss
- Stage 4 (eGFR 15–29): Severe loss
- Stage 5 (eGFR below 15): Kidney failure
Stages 1 and 2 rarely cause symptoms. Most people discover them through routine bloodwork. Stage 3 is where many people first get flagged, and it’s also where age-related decline can blur the line. A 75-year-old with an eGFR of 55 is in a very different situation than a 35-year-old with the same number.
When Symptoms Appear
Kidney disease is often called a “silent” condition because noticeable symptoms typically don’t emerge until function drops significantly, usually below an eGFR of 30. At that point, the kidneys struggle to manage fluid balance, waste removal, and electrolyte regulation. Common symptoms in advanced stages include persistent fatigue, nausea, loss of appetite, swelling from fluid retention, trouble concentrating, and sleep problems. Shortness of breath can develop if fluid accumulates in the lungs, and blood pressure often becomes difficult to control.
At the most advanced stage (eGFR below 15), dangerous spikes in potassium can occur, which affect heart rhythm. Inflammation around the heart and nervous system changes, including personality shifts and difficulty concentrating, can also develop. These complications are why early detection through routine blood tests matters so much. By the time you feel something is wrong, a large portion of kidney function has already been lost.
eGFR in Children and Teens
Pediatric eGFR uses different equations than adult eGFR because children’s bodies produce creatinine at different rates as they grow. Newborns have their own dedicated formula for the first four weeks of life, and children older than two can be assessed with equations designed to span the full age range into adulthood. These newer “full spectrum” equations avoid the sudden jump in eGFR values that used to occur when a patient transitioned from a pediatric formula to an adult one at age 18. For children and young adults, an eGFR of 75 or above is generally where the standard equations provide reliable estimates.