Creatinine Clearance Calculator
Cockcroft-Gault kidney estimate from age, weight, sex, and creatinine.
What it does
Creatinine clearance estimates how fast kidneys filter waste from blood. Doctors still use it to set doses for drugs that leave through the kidneys, because too high a dose in slow kidneys turns toxic and too low a dose in fast kidneys does nothing.
The tool above runs the 1976 Cockcroft-Gault equation: (140 minus age) times weight in kg, divided by 72 times serum creatinine, times 0.85 for women. Enter age, sex, weight, and one creatinine value in mg/dL, in either unit system.
The default tells a full story. A 65 year old man weighing 176.4 lb with creatinine 1.1 mg/dL clears about 75.8 mL/min, landing in the mild decrease band (G2). The metric mirror at 80 kg returns the same figure, since the math converts pounds behind the form.
Know what the number is not. The National Kidney Foundation now advises moving drug dosing toward race free eGFR equations, because Cockcroft-Gault came from 249 white men with an estimated female adjustment and pre standard creatinine assays. Staging chronic kidney disease belongs on eGFR, albuminuria, and a clinician, never on this page alone.
Treat every result here as orientation for a conversation with a doctor or pharmacist. Kidney numbers guide real prescriptions, and only the care team sees the full chart.
How to use
- Pick imperial or metric for the weight entry.
- Type age between 18 and 120.
- Select male or female for the 0.85 factor.
- Type weight in lb or kg.
- Type serum creatinine in mg/dL from a recent lab.
- Read clearance first, then the stage band, and take both to the prescriber.
Formula
- CrCl
- Estimated creatinine clearance in mL/min.
- age
- Age in years.
- weight
- Body weight in kg (converted from lb when needed).
- Scr
- Serum creatinine in mg/dL.
- 0.85
- Female adjustment for lower muscle mass.
Age carries the prediction: each passing year lowers the numerator by one weight unit. Weight stands in for muscle, which is exactly why the formula overreads in obesity and underreads in frailty. Modern IDMS standardized creatinine assays read about 12 % lower than the 1970s assays behind the original fit, another reason dosing guidance is shifting to eGFR.
Worked example
Example: man, 65, 176.4 lb, creatinine 1.1
Imperial defaults already filled in the form.
- Convert weight: 176.4 / 2.20462 = 80.0 kg used.
- Numerator: (140 - 65) x 80.0 = 75 x 80.0 = 6000.
- Denominator: 72 x 1.1 = 79.2.
- Divide: 6000 / 79.2 = 75.8 mL/min.
- Stage: 75.8 sits in 60 to 89, a mild decrease (G2).
- Metric check: 80 kg gives the same 75.8 mL/min.
Reference table
| mL/min | Band | Meaning |
|---|---|---|
| 90 and up | G1 normal | Usual reference range |
| 60 to 89 | G2 mild | Mild decrease, confirm with eGFR |
| 30 to 59 | G3a/G3b | Moderate decrease, dosing review |
| 15 to 29 | G4 severe | Specialist dosing territory |
| Under 15 | G5 failure | Urgent specialist care |
Limits
- Built on 249 white men, so diverse bodies and the estimated female factor carry real uncertainty.
- Assumes steady creatinine; useless during acute kidney injury or rapid change.
- Muscle extremes mislead: amputees and bodybuilders need measured clearance, not estimates.
- Does not replace race free eGFR for diagnosing or staging chronic kidney disease.
Common mistakes
- Entering creatinine in micromol/L. The formula wants mg/dL; divide micromol by 88.4 first.
- Using total weight in severe obesity without asking about adjusted body weight.
- Reading one high creatinine as permanent failure instead of repeating the lab.
- Staging CKD from this number instead of eGFR plus urine albumin.
- Adjusting prescriptions solo instead of through the prescriber or pharmacist.
Try it yourself
Quick checks. Answers sit tucked under each question.
Woman, 55, 70 kg, creatinine 0.9. Clearance?
(85 x 70) / (72 x 0.9) x 0.85 = 78 mL/min, mild decrease (G2).
Same man but creatinine 2.2. Result?
6000 / 158.4 = 37.9 mL/min, moderate to severe (G3b). Doubling creatinine roughly halves clearance.
Why does age lower the result at fixed weight and creatinine?
The numerator (140 - age) shrinks every year, mirroring the slow fall of filtration with age.
Questions
What does 75.8 mL/min mean?
Mildly reduced filtration estimates; many 65 year olds sit here. A clinician reads it with eGFR and history.
Why multiply by 0.85 for women?
Women average less muscle, hence less creatinine at the same filtration. The factor approximates that gap.
Which weight should obese patients use?
Ask the prescriber. Adjusted or ideal body weight often replaces total weight for dosing.
Is this the same as eGFR?
No. eGFR uses newer equations validated against measured GFR; Cockcroft-Gault estimates creatinine clearance.
What units does creatinine use here?
mg/dL. Convert micromol/L by dividing by 88.4.
Can dehydration change the number?
Yes. Low fluid volume raises creatinine and drops the estimate until rehydrated.
Sources
- National Kidney Foundation: Cockcroft-Gault equation
- NIH StatPearls: Creatinine Clearance (NCBI Bookshelf)