Calculate eGFR from Creatinine: CKD-EPI 2021 and Its Limits

The 2021 CKD-EPI creatinine equation estimates adult kidney filtration from serum creatinine, age, and the equation's sex parameter. It produces a value in mL/min/1.73 m², standardized to a reference body surface area. It cannot establish the cause of a low value or diagnose CKD from one blood test.

Our eGFR calculator uses this race-free equation. Your laboratory may use a different equation; start with its report and ask which method it uses when results differ.

Inputs and unit checks

Use serum creatinine from a blood test, age in completed years, and the sex parameter used for clinical interpretation. This equation is intended for adults aged 18 and older with stable kidney function. Children need a pediatric equation. For hormone therapy, altered muscle mass, or uncertainty about the sex parameter, discuss the estimate with a clinician rather than assuming one setting is universally correct.

Select the exact unit on the report. A misplaced decimal or using µmol/L as mg/dL can produce a plausible-looking but meaningless number. The creatinine unit converter helps check the conversion; it does not interpret a creatinine reference range.

The equation

NIDDK publishes the equation and its constants:

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

Scr is creatinine in mg/dL. κ is 0.7 for females and 0.9 for males; α is −0.241 for females and −0.302 for males. min selects the smaller value and max the larger. There is no race multiplier. These coefficients are properties of a population-derived equation, not measurements of an individual's muscle mass.

Worked example: 55 years, female parameter, creatinine 1.0 mg/dL

1. Scr/κ = 1.0/0.7 ≈ 1.429.
2. The minimum term is 1, and the maximum term is approximately 1.429.
3. 142 × 1^−0.241 × 1.429^−1.200 × 0.9938^55 × 1.012 ≈ 66.5.
4. Report approximately 67 mL/min/1.73 m², depending on rounding.

This falls in G2, but G2 alone is not a CKD diagnosis. Urine findings, previous results, and chronicity are still needed. A calculator's decimal precision should never be interpreted as equal precision in the underlying kidney estimate.

Why the laboratory result may differ

Check whether the laboratory used CKD-EPI 2021, an older CKD-EPI equation, MDRD, or a locally recommended method. Differences may also reflect rounding, standardized assay results, or a report that displays only a threshold such as “≥90.” Recalculating a threshold using an assumed creatinine value does not recover the missing measured information.

When this estimate is less reliable

Creatinine is influenced by muscle mass, diet, supplements, and some medicines as well as filtration. Standard equations may mislead during acute kidney injury, pregnancy, severe muscle loss, amputation, or unusually high muscle mass. The creatinine-cystatin C equation is often useful when a more accurate estimate affects a decision, but it too has limitations.

Do not use a stage category to select a medicine dose. Drug labels may require creatinine clearance or an estimate without body-surface-area indexing, especially at unusual body size. Ask a clinician or pharmacist to choose the method.

What to do with the number

Keep the report, check the inputs once, compare prior values, and ask about urine albumin. Use the age and CKD guide for interpretation. If there is a sudden fall, seek assessment instead of repeatedly recalculating or changing hydration and medication yourself.