About the GFR Calculator
GFR Calculator helps estimate the key numbers involved in other decisions. It is designed for quick scenario comparison: enter a realistic set of values, calculate the result, then change one assumption at a time to see what has the greatest effect. Unlike a static table, the result responds to your inputs and keeps the calculation in your browser. Health and fitness results are population-based estimates. They can support a conversation or planning process, but they do not determine an individual diagnosis, treatment, or safe activity level.
How to use this calculator
Enter values that match your situation and select Calculate result. Review the main result and its supporting figures, then change one input at a time to compare scenarios. Results are rounded for readability while the calculation retains additional precision internally.
Information you will need
- Age
- Sex
- Creatinine
How the calculation works
2021 CKD-EPI creatinine equation (race-free). Read the primary result together with the supporting values rather than focusing on one number alone. A useful estimate should make its assumptions visible. If the answer looks surprising, verify the unit, rate, time period, and whether the entered value is gross or net. Run a conservative and an optimistic scenario to understand the range of possible outcomes.
Formula or method
eGFR = 142 × min(Scr/k)a × max(Scr/k)-1.2 × 0.9938age.
Worked example
Age 45, creatinine 1.0.
The example is illustrative rather than a recommendation. Use your own verified values and keep all monetary or measurement units consistent. When comparing alternatives, save or note each result so the assumptions do not become mixed.
How to interpret the result
The primary output answers the main question posed by the gfr calculator, while the additional cards provide context. A result with many decimal places is not necessarily more certain. The displayed precision makes comparison easier, but uncertainty in the inputs can be larger than the rounding difference.
Look for trends and ranges instead of treating a single estimate as a pass or fail result. If the output conflicts with symptoms, professional advice, or a direct measurement, rely on appropriate professional assessment.
Limitations and important notes
The gfr calculator cannot account for every factor that affects an individual result. Measurement technique, hydration, body composition, medication, pregnancy, illness, training status, and normal biological variation may matter. Do not use an estimate to diagnose a condition, select medication dosage, decide whether to drive, or ignore symptoms. A qualified professional can interpret measurements in the context of history and appropriate testing.
Frequently asked questions
What does my GFR number mean?
GFR measures how well your kidneys filter your blood, in mL/min/1.73 m². Roughly: 90+ is normal, 60-89 mildly decreased, 45-59 moderately decreased, 30-44 severely decreased, 15-29 severe, and below 15 is kidney failure. But a single result is not a diagnosis. eGFR must stay below 60 for at least three months, alongside other markers such as urine protein, before kidney disease is confirmed. Always discuss your result with a healthcare provider.
What factors affect my GFR?
eGFR equations use age, sex, and serum creatinine (or cystatin C). Many non-kidney factors move creatinine, including muscle mass, bodybuilder or amputee status, dietary habits and creatine supplements, certain medications, and hydration. So a low number can appear without true kidney disease. Age alone lowers eGFR in everyone. For this reason, providers interpret eGFR with context, and trends over time plus urine tests matter much more than any single value.
What is a normal eGFR for my age?
eGFR naturally declines with age. Population averages from large surveys are roughly 116 at ages 20-29, 107 at 30-39, 99 at 40-49, 93 at 50-59, 85 at 60-69, and 75 at 70 and older. So an eGFR around 80 at age 70 may be entirely normal. Providers interpret eGFR with age in mind, and kidney disease is diagnosed by persistently low values combined with evidence of kidney damage, not by one number alone.
What is the difference between GFR and eGFR?
GFR is your kidneys' actual filtration rate, which is difficult to measure directly because it requires injected marker substances and timed collections. eGFR is an estimate calculated from a simple blood test, usually creatinine or cystatin C, combined with your age and sex. The CKD-EPI equations are the recommended standard for estimating it. eGFR is accurate enough for most clinical decisions but becomes less precise at higher values, so trends across repeated tests matter more than single readings.
Why was race removed from the GFR calculation?
In 2021, the National Kidney Foundation and American Society of Nephrology recommended race-free CKD-EPI equations after evidence showed race-based coefficients overestimated GFR in Black patients, which could delay kidney care and transplant referrals. Race is not a reliable biological proxy for kidney function, and including it could worsen health disparities. Removing the race variable changes some results, generally lowering estimates for people previously classified as Black and raising them for others, while overall performance remains acceptable for routine clinical use.
What is cystatin C, and when is it used?
Cystatin C is a small protein produced by all nucleated cells and freely filtered by the kidneys. It is less influenced by muscle mass, diet, and supplements than creatinine, so it is useful when creatinine may be misleading, such as in bodybuilders, amputees, vegans, or older adults. Using creatinine and cystatin C together gives a more accurate eGFR, especially near decision points like drug dosing. Your provider may order cystatin C as a confirmatory test for borderline results.
My eGFR is low. What should I do next?
Do not panic. A single low reading can have non-disease causes such as dehydration, muscle mass, medication timing, or lab variation, and eGFR naturally declines with age. Your provider will likely repeat the test, add a urine albumin-to-creatinine ratio, and review your history before diagnosing anything. If kidney disease is confirmed, early steps, including blood pressure control, diabetes management, avoiding NSAIDs, and diet changes, slow progression. Ask your care team for a personalized plan.