Creatinine Clearance Calculator
Estimate kidney function as creatinine clearance (CrCl) in mL/min using the Cockcroft-Gault equation. Pharmacists and clinicians use it to adjust drug doses in renal impairment.
Last updated: May 2026
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About this calculator
Creatinine Clearance (CrCl) approximates glomerular filtration rate (GFR) by estimating how efficiently the kidneys clear creatinine — a metabolic by-product of muscle activity — from the blood. The Cockcroft-Gault equation is CrCl (mL/min) = [(140 − age) × weight (kg)] / [72 × serum creatinine (mg/dL)], multiplied by 0.85 in females to account for lower average muscle mass and therefore lower creatinine production at any given serum level. Serum creatinine is measured in mg/dL from a routine venous blood sample; if your lab reports in µmol/L, divide by 88.4 before entering the value. A normal CrCl is roughly 90–120 mL/min in young adults and declines by approximately 1 mL/min/year after age 40 due to nephron loss. Values below 60 mL/min sustained for ≥ 3 months meet the threshold for chronic kidney disease (CKD), below 30 mL/min indicate severe renal impairment, and below 15 mL/min define kidney failure (CKD stage 5). Edge cases: the formula assumes steady-state serum creatinine, so it is unreliable in acute kidney injury where creatinine is still rising; it tends to over-estimate true GFR in obese patients (use ideal or adjusted body weight) and in elderly patients with low muscle mass; and it is invalid in pregnancy, ascites and amputation. Cockcroft-Gault remains the FDA reference for drug-dose adjustment despite the more accurate CKD-EPI eGFR replacing it for CKD staging.
How to use
Example 1 — a 65-year-old man, 75 kg, serum creatinine 1.2 mg/dL. Step 1: 140 − 65 = 75. Step 2: 75 × 75 = 5,625. Step 3: denominator = 72 × 1.2 = 86.4. Step 4: CrCl = 5,625 / 86.4 ≈ 65.1 mL/min (no female correction). Verify: a value of 65 mL/min sits in the CKD stage 2 band (60–89), consistent with mild age-related decline; check by recomputing serum creatinine in µmol/L (1.2 × 88.4 ≈ 106) and confirming the lab result. ✓ Example 2 — a 78-year-old woman, 58 kg, serum creatinine 1.1 mg/dL. Step 1: 140 − 78 = 62. Step 2: 62 × 58 = 3,596. Step 3: denominator = 72 × 1.1 = 79.2. Step 4: pre-correction = 3,596 / 79.2 ≈ 45.4 mL/min. Step 5: female correction = 45.4 × 0.85 ≈ 38.6 mL/min. Verify: 39 mL/min sits in CKD stage 3b (30–44), indicating moderate-to-severe renal impairment despite a serum creatinine that looks 'only slightly raised'. This is a classic case where the formula reveals significant drug-dose adjustment is needed — for example dabigatran would now be contraindicated in many jurisdictions, and metformin would need dose reduction or discontinuation. ✓
Frequently asked questions
What is the difference between creatinine clearance and eGFR, and which should I use?
Both estimate glomerular filtration rate but use different mathematical approaches validated in different populations. Cockcroft-Gault CrCl uses age, weight and serum creatinine with a sex correction and tends to slightly overestimate true GFR because a small amount of creatinine is secreted by the renal tubules rather than purely filtered. CKD-EPI eGFR (with or without cystatin C) is now preferred for staging chronic kidney disease, cardiovascular-risk stratification and population reporting because it was validated in larger, more diverse cohorts and reports a body-surface-normalised value (mL/min/1.73 m²). However, Cockcroft-Gault remains the FDA-preferred equation for drug-dose adjustment in renal impairment because most pharmacokinetic studies that defined the dose-adjustment thresholds were performed using Cockcroft-Gault CrCl. In practice, use whichever your local pharmacy or hospital protocol specifies, and recognise that the two values can differ by 10–15 mL/min in the same patient — particularly at the extremes of muscle mass.
Why is the 0.85 correction factor applied for females in Cockcroft-Gault?
Creatinine is produced by the steady breakdown of phosphocreatine in skeletal muscle, and women on average carry about 15% less skeletal muscle mass than men of the same age and weight. Less muscle means less creatinine entering the bloodstream every day, so any given serum creatinine in a woman corresponds to a higher true GFR than the same serum value in a man. The 0.85 multiplier was derived empirically by Cockcroft and Gault in 1976 to correct for this systematic difference. It is a coarse population-level approximation; highly muscular female athletes will have their CrCl under-estimated and sarcopenic men over-estimated. If a patient's clinical picture and the calculated CrCl appear discordant — for example, a frail elderly man with a 'normal' CrCl who has clearly dropped weight — a 24-hour urine collection or a CKD-EPI eGFR with cystatin C provides a more accurate assessment.
How does age affect creatinine clearance, and what does declining CrCl mean for medication safety?
Renal function declines naturally with age: GFR falls by approximately 1 mL/min/year after age 40 due to loss of nephrons, reduced renal blood flow, and structural sclerosis of the glomeruli. The (140 − age) term in the Cockcroft-Gault equation directly encodes this expected decline, so an 80-year-old with the same weight and serum creatinine as a 30-year-old will compute a much lower CrCl. In elderly patients, even a 'normal-looking' serum creatinine can mask significantly reduced clearance, particularly in those with low muscle mass — this is the most common reason elderly patients accumulate renally-cleared drugs to toxic levels. Practically this means dose reductions, extended dosing intervals, or substitution to a renally-safer alternative for drugs like metformin, dabigatran, apixaban (at lower doses), digoxin, gabapentin, lithium and many antibiotics including aminoglycosides and vancomycin. Always recompute CrCl when prescribing in patients over 65 and re-check periodically as renal function and weight change.
What are the common mistakes when calculating CrCl?
The most frequent error is unit confusion in serum creatinine: this formula expects mg/dL, but many laboratories — particularly outside the US — report in µmol/L. Plugging 106 µmol/L into a formula expecting mg/dL gives a CrCl of roughly 1 mL/min and a panicked clinical response; the correct conversion is µmol/L ÷ 88.4 = mg/dL. The second mistake is using actual body weight in obese patients, which over-estimates muscle-based creatinine clearance and can lead to drug overdoses; many protocols recommend ideal or adjusted body weight when BMI exceeds 30. The third is applying the formula in acute kidney injury, where serum creatinine has not yet reached steady state and CrCl is meaningless — wait for a stable creatinine over 24–48 hours or use a dynamic equation. Forgetting the female correction (or applying it twice) is another classic. Finally, do not round serum creatinine to one decimal; small differences (1.0 versus 1.2 mg/dL) can shift CrCl by 20% and tip a patient into a different drug-dosing band.
When should I not use this calculator?
Do not use Cockcroft-Gault in acute kidney injury (rapidly rising creatinine), because the formula assumes steady-state and will significantly over-estimate residual function — use dynamic equations or wait for a stable creatinine. It is unreliable in pregnancy, where altered haemodynamics raise true GFR while creatinine production is variable; use pregnancy-specific protocols instead. Patients with limb amputation, paraplegia, severe muscle wasting (e.g. cancer cachexia, advanced ALS), massive oedema or ascites have altered creatinine kinetics that the formula cannot capture — direct GFR measurement or 24-hour urine collection is needed. Children and adolescents need paediatric formulae such as Schwartz, not Cockcroft-Gault. In morbidly obese patients (BMI > 40) the formula's use of actual body weight overestimates clearance; use ideal or adjusted body weight per local protocol. Finally, for staging CKD and population-level reporting, use CKD-EPI eGFR rather than Cockcroft-Gault.