Creatinine clearance (mL/min) = (140 − age) × weight (kg) ÷ (72 × creatinine in mg/dL), multiplied by 0.85 for women.
Cockcroft-Gault gives an estimate in mL/min, and kidney guidelines do not set health bands for it. The kidney function bands most people see, G1 to G5, belong to eGFR in mL/min/1.73m², and the two numbers are not interchangeable even when they happen to look similar.
Its main use today is by prescribers, because many medicine labels still give kidney thresholds in creatinine clearance. A 2026 review notes the tension between guidelines that favor eGFR and the everyday reliance on this 1976 formula. Any decision based on it stays with the prescriber.
Read the result as a rough figure. In the original study the formula correlated with measured 24-hour clearance at 0.83, and the authors noted that age and body weight had to be in the formula for a reasonable prediction. On average, the gap between predicted and measured values was no larger than the gap between two measured collections, which says as much about the reference test as about the formula.
Every input moves the result. Each extra year of age lowers it, a higher weight raises it in direct proportion, and a higher creatinine lowers it. The 0.85 factor is the adjustment the original authors made for women. Because weight sits on the top line, a 10% error in the weight you enter becomes a 10% error in the result, so an old or rounded weight is worth updating first.
Creatinine itself shifts with things that have nothing to do with filtration. A large cooked meat meal, a hard training session, creatine supplements and dehydration can raise it, and medicines such as trimethoprim and cimetidine reduce how much of it the kidneys secrete. Each of these lowers the estimate.
Weight is where the formula is most sensitive. In a study of 590 adults, using total weight in people with a BMI of 40 or more gave an accuracy of only 12.5% and a bias of 107 mL/min against measured clearance. The formula counts muscle and fat the same, although only muscle makes creatinine.
If the result is far from what a recent eGFR suggests, the first step is to check the inputs, especially weight in kilograms and creatinine in mg/dL. A repeat creatinine under steady conditions, well hydrated and without a hard workout or large meat meal the day before, often moves the estimate more than any change of formula.
The formula assumes creatinine is stable. During an acute illness or sudden kidney change the blood level lags behind real filtration, so the estimate is unreliable until things settle. A sharp drop, or a low result with swelling or a large change in urine output, is worth raising with a clinician promptly.
Cockcroft and Gault derived the formula from 249 patients. A later review points out that the study involved only white men and was done before creatinine tests were standardized, so the formula carries assumptions that do not fit every modern lab result or every body.
A comparison with measured filtration in 271 people found the error of Cockcroft-Gault grew with body weight and BMI, on top of the age effect seen with every equation. The CKD-EPI equation had the highest accuracy in that study. In a separate study of more than 3,600 patients with stable kidney function, actual weight gave an unbiased result in underweight people, while heavier groups were better served by an adjusted weight.
The result is not adjusted to body size, and creatinine is partly secreted by the kidney tubules as well as filtered, so creatinine clearance tends to run above true filtration. The original patients were aged 18 to 92, and the formula is not meant for children or pregnancy.
Take a 60 year old man weighing 80 kg with a creatinine of 1.0 mg/dL. The formula subtracts age from 140, which gives 80, then multiplies by weight for 6,400. The bottom line is 72 times creatinine, which is 72. Dividing 6,400 by 72 gives 88.9, shown as 89 mL/min.
For a woman with the same inputs the calculator multiplies by 0.85, so 88.9 becomes 75.6, shown as 76 mL/min. For comparison, the CKD-EPI 2021 creatinine equation gives the man an eGFR of about 86 mL/min/1.73m². The two sit close here, but they drift apart as weight moves away from average.
If the same man weighed 120 kg instead, the top line would become 80 times 120, or 9,600, and the result would rise to 133 mL/min even though his kidneys had not changed. That is the weight sensitivity in action, and it is why prescribers sometimes swap in an adjusted weight.
eGFR from CKD-EPI uses creatinine, age and sex, is scaled to a standard body surface of 1.73m², and is what kidney guidelines use to stage kidney function. In head to head testing against measured filtration it has generally been more accurate than Cockcroft-Gault.
A measured 24-hour urine creatinine clearance is the reference Cockcroft and Gault built against. It avoids the formula's assumptions about age and weight, but it depends on a complete collection, and missed urine is a well known source of error. Clinicians sometimes order one when an estimate looks out of step with the person in front of them, for example at the extremes of age or body size.
When body composition is unusual, kidney guidelines point toward cystatin C, a filtration marker that depends far less on muscle, alone or combined with creatinine. For people at the extremes of weight, studies have tested ideal, adjusted or lean body weight in Cockcroft-Gault, which reduced its bias in heavier groups.
The Kidney Function panel measures the values this calculator uses. Related: creatinine, egfr, cystatin c.
A creatinine clearance calculator estimates how many millilitres of blood your kidneys clear of creatinine each minute. It uses the Cockcroft-Gault equation, which needs your age, body weight in kilograms, sex and serum creatinine in mg/dL. The result is an estimate used mainly for medication decisions, not a direct measurement of kidney function.
The calculator at the top of this page runs that equation for you. What follows explains where the number comes from, how to read it without over-reading it, and why it often disagrees with the eGFR printed on your lab report.
It estimates creatinine clearance, the volume of plasma your kidneys clear of creatinine in one minute, expressed in mL/min. Creatinine is a waste product generated at a fairly steady rate by normal muscle metabolism and removed mostly by the kidneys, so the amount sitting in your blood reflects both how much you make and how well you clear it. Cockcroft-Gault takes that relationship and approximates clearance from four easily measured inputs rather than from a timed urine collection.
Creatinine clearance and glomerular filtration rate are related but they are not the same measurement, and the Cockcroft-Gault equation is not interchangeable with the CKD-EPI equation that produces eGFR 1. A small amount of creatinine is secreted by the kidney tubules rather than filtered, so clearance tends to run slightly above true filtration. That difference is usually small in practice, but it is one reason the two numbers on your screen will rarely match exactly.
Four inputs drive the result, and each one pulls the estimate in a predictable direction. Age reduces the estimate as it rises, because the equation assumes filtration declines gradually with age. Body weight raises it, because the equation treats weight as a proxy for muscle mass and therefore for creatinine production. Serum creatinine lowers it as it rises, since more creatinine left in the blood implies less being cleared. Sex applies a multiplier for women, reflecting an average difference in muscle mass rather than anything about kidney tissue itself.
The weight input is the part people get wrong most often. The original equation was built with actual body weight, but in people who are underweight, obese or carrying significant fluid, actual weight can distort the result. If your weight includes substantial oedema, the estimate is likely to read high.
Units matter too. The equation here expects creatinine in mg/dL. If your report gives µmol/L, divide by 88.4 before entering it.
Your result is a number in mL/min that places you in a broad band, and the bands below are the ones commonly used to frame medication and follow-up decisions. None of them is a diagnosis, and a single value never defines kidney health on its own.
An estimate in the usual adult range. It is reassuring in context, though it does not rule out early kidney changes that show up first in urine protein rather than in blood creatinine.
A mildly reduced estimate. This is common with increasing age and, on its own, often reflects normal age-related decline rather than disease. It is worth tracking over time rather than reacting to once.
A moderately reduced estimate. Many medication labels change their guidance around the 50 and 30 mL/min marks, so this band frequently affects which drugs are suitable and at what level. Bring it to a clinician so the trend and the cause can be assessed properly.
A markedly reduced estimate. This is a result worth discussing with a clinician promptly rather than at your next routine visit.
A very low estimate. This calls for prompt clinical review. Never ignore a result in this range, even if you feel completely well.
Unusually high results, above roughly 120 to 130 mL/min. A high estimate is not automatically good news. It can simply reflect a large body weight entered into the equation, but it can also reflect genuinely increased filtration. Drug exposure research in atrial fibrillation has specifically examined patients whose estimated creatinine clearance exceeded 100 mL/min, because an unusually high estimate may change expected blood levels of a renally cleared medication 2. Studies suggest that in some autoimmune kidney disease, clearance can run high while serum creatinine still reads normal, which may obscure early kidney involvement 3.
Whatever band you land in, the useful habit is observation, then context, then conversation. The value shows one snapshot, the trend across repeat tests shows more, and a clinician reading both alongside your history is the only person positioned to act on it.
Because the equation infers creatinine production from age, weight and sex, and those proxies fail in anyone whose body composition is unusual. Research suggests that estimates of creatinine clearance vary meaningfully depending on which weight descriptor and which equation are used, enough to move a result into a different band 4. The practical consequences of that variability have been debated in the nephrology literature for years, including whether the formula should still be used at all in its original form 5.
The situations that most often push the estimate away from reality are worth knowing.
High or low muscle mass. A heavily muscled person produces more creatinine, which raises serum creatinine without any loss of filtration, and the estimate reads low. Someone with low muscle mass, significant weight loss, an amputation or advanced illness produces less, and the estimate reads high.
Creatinine that is still moving. Cockcroft-Gault assumes a steady state. If creatinine is rising or falling day to day, the equation is describing yesterday rather than today. Model-based work in critically ill patients was developed precisely because clearance is unstable in that setting and a single static estimate can mislead 6. Comparisons of methods in acute brain injury have likewise found that different approaches to estimating clearance do not agree closely in acutely ill patients 7.
Recent diet and training. A large meat intake or creatine supplementation can raise serum creatinine. So can a hard resistance session in the days before the draw. Neither means your kidneys changed.
Hydration and assay differences. Dehydration concentrates blood and nudges creatinine up. Laboratories also differ slightly in how they measure it, which is one reason reference ranges vary by lab, age and sex.
The eGFR on your lab report comes from a different equation, usually CKD-EPI, which reports in mL/min/1.73 m2 after adjusting to a standard body surface area, while this calculator reports raw mL/min for your actual body size. That single difference explains much of the gap between the two numbers, and the two equations are not equivalent tools.
Both survive for historical and practical reasons. Many medication labels were written using Cockcroft-Gault creatinine clearance, so pharmacists and prescribers kept using it to stay aligned with those labels. Meanwhile eGFR became the standard for staging and monitoring kidney function. A National Kidney Foundation workgroup consensus has argued for moving medication-related decision-making away from Cockcroft-Gault creatinine clearance toward race-free eGFR across healthcare settings 8. For a reader checking their own labs, the sensible position is to treat this calculator as context for your eGFR, not as a replacement for it.
Mostly in deciding whether and how a renally cleared medication is used, and in flagging people who need closer kidney follow-up. In anticoagulation, estimated clearance helps determine suitability, and drug exposure changes at the high end of the range 2. In emergency care, lower creatinine clearance is associated with worse clinical outcomes in patients presenting with atrial fibrillation 9. In intensive care, where creatinine rarely holds still, clinicians lean on repeated measurement rather than a one-off estimate.
None of those decisions is one you make from a web calculator. Choosing a medication, adjusting one or stopping one belongs to a licensed provider who can see your full picture.
Start with the input itself, serum Creatinine, because the calculator is only as good as that value and a single creatinine can be swayed by training, protein intake and hydration. Read it next to your eGFR, your blood urea nitrogen and, ideally, a urine albumin to creatinine ratio, since early kidney change often appears as protein in urine before creatinine moves at all.
Cystatin C is the other marker worth knowing about. It is produced more independently of muscle mass, which makes it useful when body composition is unusual in either direction and the creatinine-based estimate looks implausible. Electrolytes, uric acid and blood pressure round out the picture, because kidney function rarely changes in isolation.
Creatinine, the input this calculator depends on, is part of FitScript's Organ Health panel, which covers kidney and liver markers alongside the rest of the membership's 150+ biomarkers tested per year. Results are interpreted by Atlas, FitScript's AI health advisor, so the number is read as a trend across repeat draws rather than as a one-off reading.
Talk to a clinician whenever the estimate sits below about 60 mL/min, whenever it drops noticeably between tests, or whenever it is low alongside symptoms such as swelling, persistent fatigue, foamy urine or a change in how much you are passing. A result below roughly 30 mL/min, or any sudden fall, is worth discussing with a clinician promptly.
Also raise it if you take medications cleared by the kidneys, if you live with diabetes or high blood pressure, or if the estimate simply does not match how you look and feel. Bring the actual lab report, the units and the date, since the interpretation depends on all three. This article is educational and is not medical advice, and any result or treatment decision should be discussed with a clinician or licensed provider who knows your history.
For related reading, see Creatinine for what the marker measures, how do i lower creatinine for the everyday factors that move it, and why is cystatin c better than creatinine for when a muscle-independent marker gives a clearer read.
Cockcroft-Gault creatinine clearance is in mL/min and uses body weight. eGFR from the CKD-EPI equations is scaled to a standard body size, in mL/min/1.73m², and does not use weight.
Yes. The original equation uses weight in kg. To convert pounds, divide by 2.2.
Cockcroft and Gault set the estimate for women 15% below the estimate for men in their original paper, which is what the 0.85 factor applies.
Lower estimates are common with increasing age, and interpretation varies by lab, age and sex. A single number never defines kidney health on its own, so read it alongside your eGFR and urine results and discuss it with a clinician.
Subtract your age from 140, multiply that by your body weight in kilograms, then divide by 72 times your serum creatinine in mg/dL. For women, multiply the result by 0.85. The calculator above does this for you and removes the arithmetic errors that creep in when people convert units or use the wrong weight.
They come from different equations and are reported differently. eGFR usually comes from CKD-EPI and is adjusted to a standard body surface area, while Cockcroft-Gault reports raw mL/min for your actual body size. The two are not equivalent, so expect them to differ, especially if your body size is well above or below average.
The original equation used actual body weight, but in people who are obese, underweight or fluid overloaded, that can distort the result. Published work has suggested calculating more than one version and reading the resulting range rather than a single figure. If you are unsure which weight applies to your situation, ask the clinician or pharmacist reviewing your results.
Divide the value in µmol/L by 88.4 to convert it to mg/dL, then enter that number. Entering µmol/L directly will produce a result that is far too low and meaningless.
The 0.85 multiplier reflects an average difference in muscle mass between sexes, not a difference in kidney tissue. Because creatinine comes from muscle, less muscle means less creatinine produced, and the equation adjusts for that assumption. Like every assumption in the formula, it fits averages better than individuals.
Yes. Heavy resistance training, a large meat intake and creatine supplementation can all raise serum creatinine without any change in kidney filtration, which lowers the calculated clearance. Standardising the days before a blood draw, and comparing repeat tests taken under similar conditions, makes the trend far more informative than any single value.
A timed urine collection measures clearance directly rather than estimating it, which can be useful when body composition is unusual or the estimate looks implausible. It is also easy to collect incompletely, which introduces its own error. Whether it is worth doing is a decision for the clinician managing your care.
That depends on your baseline, your medications and any existing conditions, so the interval is set by the clinician reviewing your results. As a general principle, kidney markers are most useful as a trend, so repeat testing under similar conditions tells you more than a single reading ever will.