eGFR Calculator (CKD-EPI 2021)
Estimate your kidney function (eGFR) from a routine creatinine blood test using the race-free CKD-EPI 2021 equation. Enter your age, sex and serum creatinine to get your eGFR and KDIGO GFR category.
Estimate Kidney Function from a Creatinine Blood Test
eGFR Formula
Where:
- \(S_{cr}\) — serum creatinine in mg/dL (if your lab reports µmol/L, divide by 88.4)
- \(k\) — 0.7 for female, 0.9 for male
- \(\alpha\) — \(-0.241\) for female, \(-0.302\) for male
- \(\text{Age}\) — age in years (valid for adults 18 and over)
- \(1.012\) — multiplier applied only to females
This is the race-free CKD-EPI 2021 creatinine equation published by Inker et al. in the New England Journal of Medicine (2021). It estimates the glomerular filtration rate — the volume of blood the kidneys filter per minute, normalised to a body surface area of 1.73 m² — from a single creatinine measurement, age and sex.
eGFR – Calculation Example
Example: a 45-year-old man has a serum creatinine of 1.0 mg/dL on a routine blood test.
\[ k = 0.9, \quad \alpha = -0.302, \quad \frac{S_{cr}}{k} = \frac{1.0}{0.9} = 1.111 \]
\[ \mathrm{eGFR} = 142 \times \min(1.111, 1)^{-0.302} \times \max(1.111, 1)^{-1.200} \times 0.9938^{45} \]
\[ \mathrm{eGFR} = 142 \times 1 \times 0.881 \times 0.756 \approx 94.6 \]
Result: eGFR ≈ 94.6 mL/min/1.73 m² — KDIGO category G1 (normal or high).
How to Use the eGFR Calculator
- Enter your Age in years (the calculator accepts 18–120, as the equation is validated for adults).
- Select your Sex — male or female, as this changes the equation coefficients.
- Enter your Serum creatinine value from your blood test report.
- Choose the correct Unit — mg/dL or µmol/L — as shown on your lab report. The calculator converts µmol/L to mg/dL automatically.
- Read your Estimated GFR (eGFR), the GFR category and an interpretation of what the result means.
What Is eGFR and Why Does It Matter?
The estimated glomerular filtration rate (eGFR) is the best widely available measure of how well your kidneys are filtering blood. Healthy kidneys filter roughly 90–120 mL/min per 1.73 m² of body surface area. As kidney function declines — whether from chronic kidney disease (CKD), diabetes, high blood pressure or ageing — the eGFR falls. Because the kidneys can lose a large share of their function before symptoms appear, the eGFR is the key early-warning number on routine blood work.
Creatinine is a waste product of muscle metabolism that is cleared almost entirely by the kidneys, so its blood level rises as filtration drops. However, creatinine also depends on muscle mass, diet and age, which is why the CKD-EPI equation combines it with age and sex to produce a more accurate estimate than creatinine alone. The 2021 version removed the race coefficient used in older equations, making it the current standard recommended by KDIGO and the US NKF–ASN task force.
The result is expressed in mL/min/1.73 m² and mapped to the KDIGO GFR categories:
| Category | eGFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mild to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure |
Note that a single eGFR value is not a diagnosis. Chronic kidney disease is defined by abnormalities persisting for at least 3 months, and a mildly low eGFR in an older adult can reflect normal ageing. Doctors also pair the eGFR with a urine albumin-to-creatinine ratio (ACR) to stage CKD fully.
Assumptions and Limitations
- Adults only: the CKD-EPI 2021 equation is validated for people aged 18 and over. For children, separate pediatric equations are used.
- Stable kidney function: the equation assumes a steady state. During acute kidney injury, when creatinine is changing rapidly, the eGFR is unreliable.
- Not accurate at extremes: estimates are less reliable for people with very high muscle mass (bodybuilders), amputations, severe illness, pregnancy, or a vegetarian/very high-meat diet, since these all shift creatinine independently of kidney function.
- Other causes of creatinine shifts: some medications (e.g. trimethoprim, cimetidine) and intense exercise just before the blood draw can raise creatinine without reducing true kidney function.
- An estimate, not a measurement: a true measured GFR (from iothalamate or iohexol clearance) can differ from the eGFR by 20% or more in individual patients.
- Medical disclaimer: this calculator is for information only and does not replace professional medical advice. Always discuss abnormal results with your doctor.
Related Calculators
If you are monitoring kidney or cardiovascular health, you may also find these useful: for patients on hemodialysis, the Dialysis Dose (Kt/V) calculator assesses treatment adequacy; the Mean Arterial Pressure calculator helps track blood pressure control, a key factor in slowing kidney disease; and the Framingham Heart Disease Risk calculator estimates your cardiovascular risk, which rises alongside reduced kidney function.
Frequently Asked Questions
What is a normal eGFR for my age?
A healthy young adult typically has an eGFR of 100–120 mL/min/1.73 m², but GFR falls gradually with age — roughly by about 1 mL/min per year after 40. An eGFR of 60–89 is common and often harmless in people over 70, whereas the same value in a 25-year-old may warrant a closer look. Age alone does not define "normal"; doctors interpret your result together with urine tests and your overall health. Discuss persistently low values with your doctor.
Why does my lab report show a different eGFR than this calculator?
Most differences are small and come from two sources. First, some labs still use the older 2009 CKD-EPI equation or the MDRD equation, which include a race coefficient and give Black patients a higher result than the 2021 race-free equation. Second, labs may round creatinine differently or restandardize the assay. If the discrepancy is large (more than about 10%), check whether your lab used a different equation and confirm the creatinine value and unit you entered.
How do I convert my creatinine between mg/dL and µmol/L?
To convert µmol/L to mg/dL, divide by 88.4; to go the other way, multiply by 88.4. For example, a creatinine of 80 µmol/L equals about 0.90 mg/dL. US labs usually report mg/dL, while labs in Europe, Canada, Australia and much of Asia report µmol/L. This calculator accepts either unit — just make sure the value and the unit you select match your lab report, or the result will be wrong.
Can an eGFR be above 100, and is that a problem?
Yes, the CKD-EPI equation can produce values above 100 mL/min/1.73 m², especially in young adults with low creatinine. There is no such thing as "too high" an eGFR from this equation — values above 90 fall into category G1 (normal or high). A genuinely abnormally high measured GFR (hyperfiltration) is a separate concept seen in early diabetes, but it cannot be diagnosed from this calculation alone. If you have diabetes, discuss screening for kidney damage with your doctor.
How accurate is eGFR, and how much can it change between tests?
The CKD-EPI 2021 equation estimates GFR within about 20% of the true measured value for most people, so an eGFR of 60 could reflect a true GFR of roughly 48–72. Day-to-day variation in creatinine, hydration, recent meals and exercise can shift the result by several points. That is why doctors never diagnose CKD from one test — the definition requires reduced kidney function or kidney damage persisting for at least 3 months.
What is the difference between eGFR and creatinine clearance?
eGFR is calculated from serum (blood) creatinine and estimates the kidneys' filtering capacity. Creatinine clearance, often estimated with the Cockcroft-Gault formula, is based on urine or serum creatinine and is not normalized to body surface area. Historically, creatinine clearance was used to dose medications, and some drug labels still reference it. Modern practice prefers eGFR for diagnosing kidney disease; medication dosing should always follow your doctor's or pharmacist's guidance.
Is there a more accurate test than creatinine-based eGFR?
Yes. Cystatin C is another blood marker that is less affected by muscle mass and diet, and a combined creatinine–cystatin C equation (CKD-EPI 2021) is more accurate than creatinine alone. Your doctor may order it if your creatinine-based eGFR is borderline or if you have unusual muscle mass, obesity, or a vegetarian diet. The gold standard remains a directly measured GFR using markers like iohexol, but this is rarely needed in routine care.