How to Calculate eGFR from Serum Creatinine (CKD-EPI 2021)

Your lab report shows a serum creatinine value — but to actually understand kidney function, you need to convert that creatinine into an eGFR. The good news: you do not have to do the math by hand. This guide explains exactly what goes into the calculation, the current formula, and how to get your result in seconds with our free eGFR calculator.

What you need to calculate eGFR

The CKD-EPI 2021 equation — the formula recommended by the National Kidney Foundation and the American Society of Nephrology — uses just three inputs:

1. Serum creatinine — from your blood test, in mg/dL or µmol/L.
2. Age — in years (the equation is validated for adults 18 and older).
3. Sex — male or female, which adjusts for typical differences in muscle mass.

That is it. Notably, the modern equation does not use race — the 2021 update removed it to make results more equitable. Read the full background in CKD-EPI 2021 vs MDRD.

The CKD-EPI 2021 creatinine equation

For reference, here is the race-free CKD-EPI 2021 creatinine formula:

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^Age × (1.012 if female)

Where Scr is serum creatinine in mg/dL, κ is 0.7 for females and 0.9 for males, and α is −0.241 for females and −0.302 for males.

You do not need to memorize or solve this. Any trustworthy calculator — including ours — applies it instantly and handles unit conversion for you.

Step-by-step: calculate your eGFR

1. Find your serum creatinine on your lab report and note the unit (mg/dL or µmol/L).
2. Open the eGFR calculator and pick the matching unit.
3. Enter your creatinine value.
4. Enter your age in years.
5. Select your sex (male or female).
6. Click Calculate eGFR to see your estimated kidney function and CKD stage.

If your report also lists cystatin C, you can enter it for the more accurate combined creatinine-cystatin C equation — but it is optional.

Worked example

Imagine a 55-year-old woman with a serum creatinine of 1.0 mg/dL:

• Creatinine: 1.0 mg/dL
• Age: 55
• Sex: Female

Plugging these into the CKD-EPI 2021 equation gives an eGFR of roughly 76 mL/min/1.73 m² — stage G2 (mildly decreased), which at age 55 may be worth monitoring but is not automatically kidney disease. See eGFR 60 meaning for how to interpret mid-range values.

The same creatinine in a 55-year-old man yields a slightly different eGFR because of the sex coefficient — another reason to always enter the correct sex. More in eGFR for women vs men.

Units: mg/dL vs µmol/L

Labs around the world use two different creatinine units, and mixing them up produces wildly wrong results:

To convert manually: 1 mg/dL ≈ 88.4 µmol/L. But again, a good calculator does this automatically — just choose the unit printed on your report.

How accurate is the calculated eGFR?

The CKD-EPI 2021 equation is highly accurate for most adults with stable kidney function. A few caveats:

• It is an estimate, not a direct measurement; true GFR requires complex tests.
• Accuracy drops at the extremes of muscle mass (very muscular people or those with muscle-wasting), in pregnancy, and during acute kidney injury.
• A single value is not diagnostic — CKD requires abnormalities for more than three months.

For unusual situations, cystatin C-based equations may be more reliable.

Tips for an accurate calculation

A few practical tips improve the reliability of your result. First, use a recent creatinine value — ideally from the last few weeks — because kidney function can change over time. Second, double-check the unit printed on the report; entering a µmol/L value into an mg/dL field (or vice versa) produces a dramatically wrong eGFR. Third, enter your exact age and correct sex, since both are built into the equation. Fourth, be aware that recent intense exercise, a very high-protein meal, dehydration, or creatine supplements can temporarily raise creatinine and lower eGFR, so a result taken during those conditions may not reflect your true baseline. Finally, remember that eGFR is an estimate: for the most accurate picture, repeat the test when well-hydrated and compare trends over time rather than relying on a single value.

Takeaway

To calculate eGFR from creatinine, you only need serum creatinine, age, and sex — the CKD-EPI 2021 equation handles the rest. Get your number in seconds with our free online eGFR calculator, compare it to the normal ranges by age, and explore more answers in our kidney function FAQ.

This article is for educational purposes only and is not medical advice. Always consult a qualified healthcare professional for diagnosis and treatment.