eGFR Calculator (CKD-EPI 2021)
Estimate kidney function with the race free CKD-EPI 2021 creatinine equation.
What it does
Estimated glomerular filtration rate, or eGFR, is the standard screen for how well kidneys filter blood. Direct measurement needs timed urine and tracer infusions, so clinics estimate instead from serum creatinine, age, and sex. The CKD-EPI 2021 creatinine equation is the method the National Kidney Foundation now recommends for adults.
The tool above runs that exact equation with no race term. Enter creatinine in umol/L or mg/dL, plus age and sex. It returns eGFR in mL/min/1.73 m2, the G stage from G1 to G5, and a plain next step. Defaults describe a 50 year old man at 88.4 umol/L, so the page opens solved at 92 and stage G1.
Creatinine deserves a careful read because it is a muscle product, not a pure kidney signal. Two people with the same kidneys can report different creatinine when one carries far more muscle, eats large meat meals, or takes creatine. That is why the result screen asks for urine albumin and trend: falling eGFR across several stable readings means far more than any single number.
The 2021 update matters for fairness. Older equations multiplied results by a race coefficient, which moved Black patients across treatment thresholds for no biological reason. The race free version gives one answer per lab value, and studies found it keeps accuracy while narrowing those gaps.
Use the table to learn the stage cutoffs, then run your own labs. Values near 60 deserve a repeat test rather than worry, and values under 30 deserve a prompt clinician visit with a full medicine review.
How to use
- Pick metric (umol/L) or US (mg/dL) for creatinine.
- Enter serum creatinine from a standardized IDMS lab report.
- Enter age and sex.
- Read eGFR first, then the G stage.
- Compare with past results from the same equation.
- Add a urine albumin test before drawing conclusions.
Formula
- Scr
- Serum creatinine. Enter umol/L in metric mode or mg/dL in US mode.
- k
- 0.7 for women, 0.9 for men.
- a
- -0.241 for women, -0.302 for men.
- Age
- Age in years, 18 to 100.
Scr is serum creatinine in mg/dL (umol/L divided by 88.4). k is 0.7 for women and 0.9 for men; a is -0.241 for women and -0.302 for men. The page uses the creatinine only CKD-EPI 2021 equation without any race term, for adults 18 and older.
Worked example
Example: 50 year old man, creatinine 88.4 umol/L
A 50 year old man has serum creatinine 88.4 umol/L. Find eGFR with CKD-EPI 2021.
- Convert 88.4 umol/L to mg/dL: 88.4 / 88.4 = 1.0 mg/dL.
- Male constants: k = 0.9, exponent = -0.302. Ratio = 1.0 / 0.9 = 1.111.
- Low term: min(1.111, 1) = 1, so 1 raised to any power is 1.
- High term: 1.111 to the -1.2 = 0.881.
- Age term: 0.9938 to the 50 = 0.733. eGFR = 142 x 1 x 0.881 x 0.733 = 92.
- 92 sits at or above 90, so stage G1 (normal or high). Confirm with urine albumin and trend.
Reference table
| eGFR | Stage | Reads as |
|---|---|---|
| 90 or above | G1 | Normal or high |
| 60 to 89 | G2 | Mildly low |
| 45 to 59 | G3a | Mild to moderate |
| 30 to 44 | G3b | Moderate to severe |
| 15 to 29 | G4 | Severely low |
| Below 15 | G5 | Kidney failure |
Limits
- Adults 18 and older only. Children need CKiD equations.
- Creatinine based, so muscle extremes distort it.
- Single readings never diagnose CKD; trends plus albumin decide.
- Less accurate above 90 and during acute illness.
Common mistakes
- Mixing umol/L with the mg/dL path. Divide umol/L by 88.4 first.
- Using a non standardized creatinine value from old records.
- Reading one low value as CKD without repeat testing.
- Ignoring albumin: eGFR plus urine albumin stages risk together.
- Comparing numbers across the old race based equation.
Try it yourself
Quick checks. Answers sit tucked under each question.
60 year old woman, creatinine 1.2 mg/dL?
Ratio 1.2 / 0.7 = 1.714. eGFR = 142 x 0.524 x 0.689 x 1.012 = 52, stage G3a.
40 year old man, creatinine 0.9 mg/dL?
Ratio 0.9 / 0.9 = 1.0, so both power terms are 1. eGFR = 142 x 0.9938^40 = 111, stage G1.
Why does 88.4 umol/L match 1.0 mg/dL?
88.4 / 88.4 = 1.0 mg/dL, identical input, so both modes print 92.
Questions
What eGFR counts as normal?
About 90 or above with no other kidney signs. Below 60 on repeat tests over 3 months points toward CKD and needs urine albumin testing.
Does muscle mass change the result?
Creatinine comes from muscle, so heavy muscle mass reads lower eGFR than reality and low muscle reads higher. Cystatin C helps when muscle is unusual.
How is CKD-EPI 2021 different from 2009?
The 2009 version added a race coefficient. The 2021 race free version dropped it, so labs now report one number for everyone with the same age, sex, and creatinine.
Why do metric and US modes agree here?
Single digits differ by rounding only: 88.4 umol/L equals 1.0 mg/dL exactly, so both modes print 92 for the worked case.
What should I do after a low reading?
One reading never diagnoses CKD. Repeat the labs, add a urine albumin to creatinine ratio, and review medicines that block creatinine secretion.
What can distort creatinine short term?
Acute illness, dehydration, a heavy meat meal, creatine supplements, and some drugs shift creatinine for days. Retest when stable.