eGFR Calculator
Estimating Kidney Function From a Single Blood Value
Serum creatinine on its own is a poor guide to kidney function. It is a waste product of muscle metabolism, so a frail 80-year-old and a muscular 30-year-old can share an identical creatinine reading while their kidneys are doing very different amounts of work. The estimated glomerular filtration rate corrects for that by folding age and sex into the calculation, producing a figure that speaks to filtration capacity rather than to muscle mass. This calculator implements the CKD-EPI 2021 creatinine equation — the race-free revision that replaced the earlier version carrying a Black-race coefficient.
The Formula
The CKD-EPI 2021 creatinine equation, exactly as this calculator applies it:
κ = 0.7 (female) or 0.9 (male)
α = −0.241 (female) or −0.302 (male)
Scr = serum creatinine in mg/dL
The two-part min/max structure is what gives the equation its kink: below the sex-specific κ threshold, creatinine changes eGFR gently; above it, the steep −1.200 exponent takes over and eGFR falls away quickly. That deliberate asymmetry is why a creatinine rise from 1.0 to 1.4 costs far more filtration than a rise from 0.6 to 1.0.
eGFR Across Age, Sex and Creatinine
Every figure in this table was produced by running the equation above:
| Serum creatinine | Male, 30 | Female, 30 | Male, 50 | Female, 50 | Male, 70 | Female, 70 |
|---|---|---|---|---|---|---|
| 0.8 mg/dL | 122.1 | 101.6 | 107.8 | 89.7 | 95.2 | 79.2 |
| 1.0 mg/dL | 103.8 | 77.7 | 91.7 | 68.6 | 81.0 | 60.6 |
| 1.4 mg/dL | 69.3 | 51.9 | 61.2 | 45.8 | 54.1 | 40.5 |
| 2.0 mg/dL | 45.2 | 33.8 | 39.9 | 29.9 | 35.2 | 26.4 |
| 3.0 mg/dL | 27.8 | 20.8 | 24.5 | 18.4 | 21.7 | 16.2 |
Note the column pairs: at the same creatinine, the female estimate is consistently lower, reflecting the lower κ and the fact that a given creatinine represents proportionally more filtration burden at typically lower muscle mass.
Why the Result Says "per 1.73m²"
eGFR is reported normalised to a body surface area of 1.73 m² — a figure adopted decades ago as a stand-in for an average adult. It makes results comparable between a small patient and a large one, at the cost of being slightly wrong for anyone far from that reference size. When absolute clearance matters more than comparability, the Cockcroft-Gault creatinine clearance is often used instead, precisely because it is not surface-area normalised.
CKD Stages by GFR
The KDIGO GFR categories are the standard published bands used to describe filtration:
| Category | GFR (mL/min/1.73m²) | Description |
|---|---|---|
| G1 | 90 and above | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | Below 15 | Kidney failure |
These bands are published reference categories included here for context. This calculator returns an eGFR value only; it does not assign a stage, and a stage cannot be assigned from one reading in any case.
Where This Estimate Gets Used
- Drug dosing thresholds — a great many medications carry renal dose adjustments keyed to eGFR bands.
- Contrast and procedure planning — imaging protocols routinely reference recent eGFR.
- Longitudinal monitoring — the trend across repeated measurements carries more information than any single value.
- Understanding lab reports — eGFR is auto-calculated on most creatinine panels, and knowing the inputs demystifies why it moved.
How to Use This Calculator
- Enter Age (years).
- Enter Serum Creatinine (mg/dL). If your lab reports in µmol/L, divide by 88.4 to convert.
- Select Sex — this sets both κ and α, and applies the 1.012 female multiplier.
- Select Calculate. The output shows the eGFR along with each intermediate term, so you can see which factor is driving the result.
Related Calculations
Compare against the Creatinine Clearance Calculator, which uses Cockcroft-Gault and weight rather than surface-area normalisation, or work out the 1.73 m² reference itself with the Body Surface Area Calculator.