This GFR calculator estimates eGFR with a simplified CKD-EPI style equation. Defaults are serum creatinine 1 mg/dL, age 45, and male. On the live formula that path returns about 94.6 (displayed to one decimal). It is an educational estimate only, not medical advice.
Body size context tools such as the BMI calculator answer different questions. Energy tools like the TDEE calculator are unrelated to filtration estimates.
How the formula works
For males, κ = 0.9 and α = -0.302. Compute Scr/κ. Then eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(-1.2) × 0.9938^age. Females use κ = 0.7, α = -0.241, and multiply by 1.012.
Worked example
Scr = 1, age = 45, male. Scr/κ = 1/0.9 ≈ 1.111. min = 1, max ≈ 1.111. eGFR = 142 × 1^(-0.302) × (1.111)^(-1.2) × 0.9938^45 ≈ 94.6.
| Input | Value |
|---|---|
| Creatinine (mg/dL) | 1 |
| Age | 45 |
| Sex | male |
| κ / α | 0.9 / -0.302 |
| Estimated eGFR | about 94.6 |
How to use the fields
- Serum creatinine is entered in mg/dL.
- Age is in years.
- Sex selects the κ, α, and female multiplier path.
Min and max limbs
When Scr/κ is at or below 1, the α exponent applies to Scr/κ and the max limb is 1. When Scr/κ is above 1, as in the default, the α limb sees 1 and the -1.2 limb sees Scr/κ. Mixing those limbs is a common hand calculation error.
Write min and max on separate lines before multiplying so the age factor is the only remaining piece.
Common mistakes
- Treating the result as a personal diagnosis
- Using μmol/L creatinine without converting to mg/dL
- Applying male constants to a female example
- Ignoring age by omitting 0.9938^age
Educational framing only
Kidney evaluation involves labs, history, imaging, and clinical judgment. This page does not stage chronic kidney disease for care decisions. It only shows how a simplified CKD-EPI style expression responds to creatinine, age, and sex.
If a lab report already prints eGFR, compare methods and units with a clinician rather than replacing the report with this sketch.
Why age appears as a power
The 0.9938^age term gently lowers the estimate as age rises when other inputs stay fixed. Try age 45 versus age 65 with the same creatinine to see that directional effect for class discussion.
Do not invent health stories from a classroom delta. Keep the talk on arithmetic sensitivity.
Related body metrics stay separate
Weight and protein intake questions belong on tools such as the ideal weight calculator and the protein calculator. They do not compute eGFR.
Reporting habits
Say “about 94.6 educational eGFR for creatinine 1, age 45, male” rather than a bare integer. Include units mL/min/1.73m² when your course expects them.
Percent error drills against a hand sheet can use the percentage calculator after both values exist.
Sensitivity drills that stay educational
Hold age and sex fixed, then raise creatinine slightly and watch eGFR fall when the max limb grows. Hold creatinine fixed and raise age to see the 0.9938^age term pull the estimate down. Separate those experiments so students attribute the change to the correct factor.
Repeat the default male path by hand with min and max written explicitly. The live tool should match about 94.6 when rounded to one decimal. If a worksheet still prints 101 from an older sketch, reconcile by checking whether min and max were applied correctly for Scr/κ above 1.
Never escalate a classroom mismatch into a health scare. Recheck arithmetic first, then talk with a clinician about real labs when health is the question.
Write the full expression with κ and α substituted before multiplying. That slow layout catches missing age powers and swapped min/max limbs more reliably than jumping to a calculator click.
State again that about 94.6 for the default male inputs is an educational estimate only, not a clinical report.
If health decisions are needed, use clinician ordered labs rather than this classroom sketch.
Limitations
No cystatin C, no race coefficients from older equations, and no clinical decision support. Educational CKD-EPI style estimate only, not medical advice.