Creatinine Clearance Calculator (Cockcroft-Gault)

Creatinine clearance in brief

Creatinine clearance (CrCl) estimates how much blood plasma the kidneys clear of creatinine each minute, in mL/min. The calculator above uses the Cockcroft-Gault equation, published in 1976 and still the formula behind kidney-dose recommendations on many drug labels. It uses age, body weight, sex and serum creatinine:

CrCl (mL/min) = [(140 − age) × weight (kg)] ÷ [72 × serum creatinine (mg/dL)] × 0.85 if female

If your creatinine is reported in µmol/L, the calculator divides by 88.4 first. Unlike eGFR, the result is not adjusted to a standard body surface area – it is meant to reflect the actual filtering capacity of the person in front of you, which is why it is used for medicine dosing.

How the equation was built

Donald Cockcroft and Henry Gault derived the formula from 249 men in a Canadian hospital, comparing creatinine with 24-hour urine creatinine clearance. They found that clearance fell with age and rose with body weight, and proposed a 15% reduction for women based on their lower average muscle mass. Creatinine assays at the time were not standardised, and modern assays (traceable to isotope dilution mass spectrometry, IDMS) give slightly lower creatinine values than older methods – one reason Cockcroft-Gault tends to overestimate clearance a little today.

Despite these limitations, much of the pharmacokinetic research behind drug labels used Cockcroft-Gault, so regulators and pharmacists continue to use it when a label specifies creatinine clearance.

Creatinine clearance versus GFR

Creatinine is filtered by the glomeruli but is also secreted by the kidney tubules, by about 10–20% in healthy people and proportionally more as kidney function falls. That means true creatinine clearance is always somewhat higher than the true GFR. The Cockcroft-Gault estimate is therefore not a measure of GFR, even though the two are often used interchangeably in practice.

Worked examples

All results below were calculated with the Cockcroft-Gault equation using actual body weight:

• Man, 60 years, 80 kg, creatinine 1.0 mg/dL (88 µmol/L): (80 × 80) ÷ (72 × 1.0) = 88.9 mL/min.
• Woman, 75 years, 60 kg, creatinine 1.1 mg/dL (97 µmol/L): (65 × 60) ÷ (72 × 1.1) × 0.85 = 41.9 mL/min.
• Woman, 85 years, 50 kg, creatinine 1.0 mg/dL (88 µmol/L): (55 × 50) ÷ 72 × 0.85 = 32.5 mL/min.

The third example shows why Cockcroft-Gault matters in older, smaller people. A creatinine of 1.0 mg/dL looks normal, and the CKD-EPI 2021 eGFR for an 85-year-old woman with that creatinine is about 55 mL/min/1.73 m². The Cockcroft-Gault estimate of 32.5 mL/min is substantially lower and could change the dose of several medicines.

Interpreting creatinine clearance

There is no separate staging system for creatinine clearance, but drug labels typically use bands similar to these:

The exact cut-offs vary between medicines, so always check the specific product information. For example, some direct oral anticoagulants have dose-reduction rules based on creatinine clearance thresholds such as 50, 30 and 15 mL/min, and some antibiotics have three or four dosing bands.

Typical values by age

In healthy adults with average body size, CrCl is typically around 90–130 mL/min in young adults and declines with age, because the equation subtracts age from 140. A healthy 80-year-old weighing 70 kg with a creatinine of 0.9 mg/dL has an estimated clearance of about 65 mL/min if male and 55 mL/min if female. These lower numbers are expected and are the reason medicine doses are often reduced in older people.

A step-by-step calculation

Here is how to work through the equation by hand for a 72-year-old man who weighs 68 kg and has a creatinine of 115 µmol/L:

1. Convert creatinine to mg/dL: 115 ÷ 88.4 = 1.30 mg/dL.
2. Subtract age from 140: 140 − 72 = 68.
3. Multiply by weight: 68 × 68 = 4,624.
4. Multiply 72 by creatinine: 72 × 1.30 = 93.6.
5. Divide: 4,624 ÷ 93.6 = 49.4 mL/min.

For a woman with the same values, multiply by 0.85 to get 42.0 mL/min. The calculator performs these steps automatically and shows the result rounded to one decimal place.

Which body weight to use

The original equation used actual body weight, and this calculator does the same. However, in people with obesity, actual weight can substantially overestimate clearance, because fat contributes little to creatinine production. Common practices include:

• Actual body weight when weight is close to ideal.
• Ideal body weight (IBW) when actual weight is above ideal – IBW (kg) is approximately 50 + 0.91 × (height in cm − 152.4) for men and 45.5 + 0.91 × (height in cm − 152.4) for women.
• Adjusted body weight = IBW + 0.4 × (actual weight − IBW), often used when actual weight exceeds IBW by more than 20–30%.
• The lower of actual and ideal in people who are underweight.

Different hospitals and drug references recommend different approaches, and there is no single correct answer. If you are calculating a dose, follow your local pharmacy guidance or ask a pharmacist.

Rounding very low creatinine values

In frail older adults with very low muscle mass, creatinine can be as low as 0.5–0.6 mg/dL, leading to unrealistically high CrCl estimates. Some clinicians round creatinine up to 0.8 or 1.0 mg/dL in this situation, but studies show that this practice can underestimate clearance and is not universally recommended. It is a clinical judgement rather than a rule.

Cockcroft-Gault versus eGFR

The US FDA's 2024 guidance for industry on pharmacokinetics in patients with impaired kidney function allows either Cockcroft-Gault or eGFR for assessing kidney function in drug studies. For newer medicines, labels increasingly use eGFR; for older medicines, Cockcroft-Gault remains common. When using eGFR to dose a drug in a person with a body size far from average, some references recommend converting it to non-normalised GFR in mL/min by multiplying by the person's body surface area divided by 1.73.

Factors that affect the result

Because Cockcroft-Gault depends on creatinine, everything that affects creatinine affects the estimate:

• Muscle mass: people with high muscle mass have higher creatinine and lower estimated clearance; amputation, paralysis, frailty and malnutrition do the opposite.
• Diet: a large cooked-meat meal can raise creatinine for several hours; creatine supplements raise it more persistently.
• Medicines: trimethoprim, cimetidine, dolutegravir, cobicistat and some others reduce tubular secretion of creatinine and raise creatinine without changing GFR.
• Acute illness: in acute kidney injury, creatinine rises over days, so any equation that assumes a steady state will overestimate kidney function early on.
• Fluid overload: dilutes creatinine and can lead to overestimates.
• Pregnancy: increases GFR, and Cockcroft-Gault has not been validated in pregnancy.

Measured creatinine clearance

A 24-hour urine collection with a simultaneous blood creatinine allows clearance to be measured rather than estimated: CrCl = (urine creatinine × urine volume) ÷ (plasma creatinine × time). It can help when muscle mass is extreme, for example in people with spinal cord injury or amputations. However, collections are often incomplete, which makes results unreliable, so they are used selectively.

Special situations

Augmented renal clearance

In some critically ill patients – particularly younger people with trauma, burns, sepsis or brain injury – kidney clearance can be higher than normal, sometimes above 130 mL/min. This is called augmented renal clearance, and it can cause standard doses of kidney-cleared antibiotics to be too low. Cockcroft-Gault often fails to detect it, and measured urine creatinine clearance is sometimes used in intensive care to identify it.

Dialysis

Cockcroft-Gault should not be used in people on dialysis, because their creatinine is determined mainly by the dialysis schedule rather than by their own kidneys. Drug dosing in dialysis follows specific recommendations for each type of dialysis.

Unstable kidney function

If creatinine is rising day by day, an equation based on a single value will overestimate clearance. If creatinine is falling during recovery, it will underestimate it. In both situations, clinicians tend to dose cautiously and recheck frequently, sometimes using kinetic eGFR methods that take the rate of change into account.

Liver disease and low muscle mass

People with advanced cirrhosis often have low muscle mass and low creatinine production, and creatinine-based estimates can greatly overestimate kidney function. Cystatin C or measured GFR may be more reliable in this group.

Why kidney function matters for medicines

The kidneys remove many medicines and their active breakdown products. When clearance falls, those substances accumulate, and standard doses can lead to higher blood levels and side effects. Medicines where kidney function commonly guides dosing include:

• many antibiotics, such as penicillins, cephalosporins, fluoroquinolones, aminoglycosides, vancomycin and nitrofurantoin
• anticoagulants, including several direct oral anticoagulants and low-molecular-weight heparins
• diabetes medicines, including metformin and some sulfonylureas and DPP-4 inhibitors
• nerve-pain medicines such as gabapentin and pregabalin
• lithium, digoxin, allopurinol and some antivirals

Product information for each medicine states whether its kidney dosing bands use creatinine clearance or eGFR, and what the thresholds are.

Practical tips for medicine dosing

• Use a recent, stable creatinine value – not one from a day when the person was acutely ill.
• Record the weight used and the reason, so others can reproduce the calculation.
• Recalculate when kidney function or weight changes significantly.
• For medicines with a narrow therapeutic range, such as vancomycin, aminoglycosides, lithium or digoxin, use drug-level monitoring where available rather than relying on estimates alone.
• When CrCl and eGFR suggest different dose bands, discuss with a pharmacist.

Why CrCl results may differ between tools

Online calculators and hospital systems sometimes give slightly different results for the same person. Differences usually come from:

• the body weight used (actual, ideal or adjusted)
• whether creatinine is rounded up in older people
• the conversion factor for µmol/L (88.4 or 88.42)
• rounding of age or weight
• whether the result is capped at a maximum value, such as 120 mL/min

When results disagree, check which inputs each tool used rather than assuming one is wrong.

Questions to ask about your medicines

If you have been told your kidney function is reduced, it is worth reviewing your medicines with a doctor or pharmacist. Useful questions include:

• Do any of my regular medicines need a lower dose or a longer interval between doses at my level of kidney function?
• Which over-the-counter medicines should I avoid? Non-steroidal anti-inflammatory drugs, some indigestion remedies containing magnesium or aluminium, and certain herbal products can be a problem when kidney function is reduced.
• Should any medicines be paused if I become dehydrated, for example during vomiting, diarrhoea or fever? Many health services issue "sick day" guidance for medicines such as metformin, ACE inhibitors, angiotensin receptor blockers, diuretics and SGLT2 inhibitors.
• How often should my kidney function be rechecked?
• Was my dose calculated with creatinine clearance or eGFR, and which body weight was used?

Keeping an up-to-date list of your medicines and recent kidney results makes these conversations easier, especially when you see a new clinician or are admitted to hospital.

When to see a doctor

A low creatinine clearance on its own is not a diagnosis. It is most useful for adjusting medicines. See a doctor or pharmacist if:

• your estimated clearance is below 60 mL/min and you take regular medicines, particularly diabetes medicines, anticoagulants, pain relievers, antibiotics or medicines for epilepsy or mood
• your creatinine has risen compared with previous tests
• you have symptoms such as reduced urine output, swelling, breathlessness, nausea or confusion – these need prompt assessment
• you have diabetes, high blood pressure or heart disease and have not had kidney function and urine albumin checked in the past year

Never change a medicine dose yourself based on a calculator result.