Estimate your kidney function using the race-free 2021 CKD-EPI Creatinine equation — the current NKF/ASN-endorsed standard. Supports mg/dL and µmol/L, and shows your matching KDIGO CKD stage (G1–G5).
🔁 Switch units any time — the calculator converts µmol/L to mg/dL by dividing by 88.4 before applying the CKD-EPI 2021 formula, so results are identical either way.
Enter your sex, age, and creatinine value to estimate eGFR
This GFR calculator estimates your glomerular filtration rate (GFR) — the rate at which your kidneys filter waste and excess fluid from your blood, and the single most widely used measure of overall kidney function. Because true GFR can only be measured directly with an invasive clearance test involving an injected filtration marker, doctors instead calculate an estimated GFR (eGFR) from a routine blood test for serum creatinine, combined with your age and sex. This calculator uses the 2021 CKD-EPI Creatinine equation, the race-free formula recommended by the National Kidney Foundation (NKF) and American Society of Nephrology (ASN) Task Force in September 2021, which has since replaced the older race-based 2009 CKD-EPI and MDRD equations as the current U.S. and international standard. It supports both mg/dL, the unit most common in the United States, and µmol/L, used in most other countries, converting automatically between the two so you get an identical result either way.
eGFR is expressed in mL/min/1.73m² — milliliters of blood filtered per minute, normalized to a standard body surface area of 1.73 square meters so results are comparable across people of different sizes. The CKD-EPI 2021 equation combines your serum creatinine level with age and sex to produce this estimate, then the result is matched against the six KDIGO CKD stages (G1 through G5) that describe the general severity of reduced kidney function.
This tool is aimed at adults (18 and older) who want to understand a serum creatinine result from a recent blood test, track how their eGFR has changed between lab visits, or prepare informed questions for an upcoming doctor's appointment. It is not a screening or diagnostic tool, and it is not designed for children or adolescents, who require pediatric-specific kidney function equations.
Kidney function often declines silently for years before symptoms appear, which is why eGFR is one of the most commonly ordered values on a standard metabolic panel — particularly for people with diabetes, high blood pressure, or a family history of kidney disease, all of which are major CKD risk factors. Understanding roughly what your eGFR number and KDIGO stage mean can help you have a more informed conversation with your doctor, but it is never a substitute for that conversation.
Exactly how this GFR calculator turns serum creatinine, age, and sex into an eGFR value
Creatinine is a waste product from muscle metabolism that healthy kidneys filter out efficiently. As filtration capacity declines, creatinine builds up in the blood, so a higher Scr generally corresponds to a lower eGFR — the equation reflects this with a negative exponent applied to the Scr ratio.
GFR naturally declines gradually with age even in healthy adults. The (0.9938)^Age term applies a small, continuous downward adjustment for every year of age, rather than jumping between rigid age brackets.
Because average muscle mass — and therefore average baseline creatinine production — differs between men and women at the population level, the equation uses different Scr reference thresholds (0.7 mg/dL for women, 0.9 mg/dL for men) and a small 1.012 multiplier for women.
From entering your lab values to reading your eGFR and KDIGO stage
Sex determines which branch of the CKD-EPI 2021 equation and creatinine reference threshold (0.7 mg/dL for women, 0.9 mg/dL for men) is used.
Age must be 18 or older — the CKD-EPI equation was developed and validated on adult populations only.
Pick mg/dL (common in the US) or µmol/L (used in most other countries), matching whatever unit appears on your lab report. You can switch at any time.
Type the serum creatinine result from your most recent blood test into the field.
See your eGFR value, matching KDIGO CKD stage, and a chart showing where your result falls across the six stage bands. Read the medical disclaimer before drawing any conclusions.
Using the calculator's own default scenario — a 45-year-old woman with serum creatinine of 0.9 mg/dL
A 45-year-old woman has a serum creatinine result of 0.9 mg/dL. Since 0.9 is greater than the 0.7 mg/dL female threshold, the second female branch of the equation applies.
Explanation: An eGFR of 80.4 places this example in the "mildly decreased" KDIGO stage G2 band. On its own, a single G2 result at age 45 is not unusual and is not a CKD diagnosis — many healthy adults fall in this range, especially as age increases. Only a physician, reviewing this value alongside repeat testing over time and other markers such as urine protein, can determine whether it reflects a normal variation or an early sign of reduced kidney function warranting further evaluation.
The six KDIGO CKD stages this calculator classifies your eGFR into
| Stage | eGFR (mL/min/1.73m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high — only counts as CKD if other kidney-damage markers (e.g. proteinuria) are also present |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure |
If your result falls in G1 or G2: this generally reflects normal or mildly reduced filtration and is common even in healthy adults, particularly as age increases. It is not, by itself, evidence of chronic kidney disease unless other kidney-damage markers are also present and persist over time.
If your result falls in G3a through G5: this indicates progressively more reduced kidney function on this single test. It is not a diagnosis — only a physician can confirm CKD, which per KDIGO guidelines requires abnormal markers persisting for more than 3 months, and can recommend appropriate next steps, which may include repeat testing, additional labs, or a nephrology referral.
This calculator provides an educational estimate only and is not a medical diagnosis. A single creatinine reading and eGFR value is not sufficient to diagnose chronic kidney disease — per KDIGO guidelines, CKD requires abnormal kidney markers persisting for more than 3 months, evaluated by a physician. Never self-adjust any medication or treatment based on this tool. Always consult a doctor or nephrologist for kidney health concerns.
Educational ways people use this calculator — never as a substitute for medical evaluation
Make sense of an eGFR or creatinine value that already appears on a blood test result before discussing it with your doctor.
Log eGFR values from successive lab visits to see the general direction of change over months or years — one input for a conversation with your physician, not a diagnosis on its own.
Arrive at a nephrology or primary care visit with informed, specific questions about what a given eGFR and KDIGO stage generally mean.
People with diabetes, a major CKD risk factor, can use this tool to understand routine kidney-function screening results as part of broader care — always directed by a physician.
High blood pressure is a leading cause of chronic kidney disease; this calculator can help contextualize eGFR values ordered as part of routine hypertension management.
Some medications are dosed based on kidney function. This calculator can help you understand why a doctor or pharmacist references eGFR — it does not replace their dosing decision.
Compare a creatinine value reported in µmol/L (common outside the US) against a US-style mg/dL reading using the built-in unit toggle.
Learn why eGFR tends to decline gradually with age even in healthy adults, via the equation's age term.
Students studying nephrology, pharmacology, or clinical lab science can use the worked formula to see exactly how CKD-EPI 2021 computes eGFR.
Family caregivers managing an older relative's care can use this tool to better understand kidney-related terms and lab values discussed by the care team.
After a hospital stay involving kidney-function labs, use this calculator to understand the terminology in discharge paperwork ahead of a follow-up visit.
Build a general understanding of what "GFR," "eGFR," and "CKD stage" mean as part of broader health and wellness education.
What this GFR calculator does well, and where it can never replace professional medical evaluation
General clinical focus areas associated with each stage — informational only, always directed by your physician
| Stage | eGFR Range | General Clinical Focus (informational only) |
|---|---|---|
| G1 | ≥ 90 | Routine monitoring if risk factors (e.g. diabetes, hypertension) are present |
| G2 | 60–89 | Blood pressure and blood sugar monitoring; general lifestyle counseling |
| G3a | 45–59 | Cardiovascular risk assessment; medication dose review by a physician |
| G3b | 30–44 | Nephrology referral often considered; anemia and bone-mineral screening |
| G4 | 15–29 | Kidney-replacement therapy planning discussions with a nephrologist |
| G5 | < 15 | Dialysis or transplant evaluation typically indicated |
Summary: This free GFR calculator uses the race-free 2021 CKD-EPI Creatinine equation to give you an educational eGFR estimate and matching KDIGO CKD stage from serum creatinine, age, and sex, in mg/dL or µmol/L — a starting point for understanding your kidney health, never a diagnosis. Pair it with related tools like the Body Surface Area Calculator and BMI Calculator for a fuller picture of body composition and clinical context.
Common questions about GFR, eGFR, and CKD staging
Official guidance to complement this calculator — not a substitute for licensed medical advice
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