What's the difference between GFR and eGFR?

GFR is the true filtration rate, measured directly via inulin clearance (the gold standard, but expensive and rarely done clinically). eGFR (estimated GFR) is calculated from creatinine or other markers using equations like CKD-EPI. This calculator provides eGFR.

Why was the CKD-EPI equation updated in 2021?

The previous version included a race-based multiplier that incorrectly suggested Black patients had better kidney function at the same creatinine level. This masked disease, delayed diagnosis, and perpetuated racial disparities. The 2021 update removed race, making the equation more equitable and accurate for all populations.

Can I use this to diagnose chronic kidney disease?

No. A low GFR result suggests you should see a doctor, but CKD diagnosis requires two eGFR measurements ≥90 days apart, plus clinical assessment. One low result could reflect dehydration, medication effects, or lab error.

My creatinine is normal but my GFR is low—is that possible?

Yes, especially in older adults or those with low muscle mass. Creatinine is produced by muscle, so elderly or frail patients may have normal creatinine despite reduced kidney function. Your doctor may order cystatin C (a creatinine-independent marker) for confirmation.

How often should I check my GFR?

If you have diabetes, hypertension, or CKD, annual testing is typical. If you're healthy with no risk factors, routine screening isn't recommended unless symptoms appear. Always follow your doctor's advice.

GFR Calculator – Kidney Function Estimator

Not medical advice. This tool is for general information and education only. It is not a diagnosis and cannot replace a doctor. Consult a qualified healthcare professional before acting on any result.

What GFR measures

Glomerular filtration rate (GFR) is the volume of fluid filtered by your kidneys per minute, measured in mL/min/1.73m². It's the gold standard for assessing kidney function and detecting chronic kidney disease (CKD) at any stage. A higher GFR indicates healthier kidney function; a declining GFR signals potential kidney damage or disease progression.

This calculator uses the CKD-EPI 2021 equation, which removed race-based adjustments that were found to mask kidney disease in Black patients and introduced bias into clinical care. The updated formula provides more accurate estimates across all populations.

The formula

GFR = 142 × (Scr/κ)^α × (0.9938)^age × (1.012 if female)

Where Scr is serum creatinine, κ is 0.7 (female) or 0.9 (male), and α is −0.208 (female) or −0.201 (male).

Worked example

Let's calculate GFR for a 55-year-old woman with a serum creatinine of 0.9 mg/dL.

Step 1: Identify the constants

Gender: Female → κ = 0.7, α = −0.208
Age: 55 years
Serum creatinine: 0.9 mg/dL

Step 2: Divide creatinine by κ

0.9 ÷ 0.7 = 1.286

Step 3: Raise to the power α

1.286^(−0.208) = 0.955

Step 4: Apply the age factor

0.9938^55 = 0.741

Step 5: Multiply by the female adjustment and base coefficient

142 × 0.955 × 0.741 × 1.012 = 101.3 mL/min/1.73m²

This result falls in the normal kidney function range (≥90 mL/min/1.73m²), indicating healthy filtration.

Interpreting your result

GFR Range	Stage	Kidney Function
≥90	1	Normal or high
60–89	2	Mildly decreased
45–59	3a	Mildly to moderately decreased
30–44	3b	Moderately to severely decreased
15–29	4	Severely decreased
<15	5	Kidney failure (dialysis/transplant)

A single low GFR doesn't automatically mean CKD; kidney function naturally varies. Diagnosis requires two measurements at least 90 days apart, plus clinical context.

Creatinine units matter

If your lab report shows creatinine in µmol/L (used in most countries outside the US), the calculator converts it to mg/dL by dividing by 88.4 before applying the equation. Always verify which unit your result uses—many labs report both.

Important limitations

This is an estimate, not professional advice. The CKD-EPI equation performs best in adults aged 18–65 with stable kidney function. It may overestimate GFR in very elderly patients, underestimate in very muscular individuals, and perform poorly in acute kidney injury. Certain medications (creatinine-elevating drugs like trimethoprim) and conditions (pregnancy, amputations, severe malnutrition) can affect creatinine levels independently of kidney function.

Always discuss your results with a doctor, especially if you have diabetes, hypertension, or a family history of kidney disease. Your clinician may order additional tests—urine albumin, cystatin C, or imaging—to confirm diagnosis and guide treatment.

Things to watch

Timing: Creatinine fluctuates slightly day-to-day. A single measurement is a snapshot; trends matter more than one number.
Lab variation: Different labs use different methods and calibrations. If your GFR drops sharply, ask whether the lab or method changed before assuming your kidneys worsened.
Muscle mass: Creatinine is a byproduct of muscle metabolism. Very muscular people may have slightly higher creatinine without kidney disease; very frail or elderly patients may have normal creatinine despite reduced function.