eGFR Calculator: Estimated GFR

eGFR in brief

The estimated glomerular filtration rate (eGFR) is the standard way to judge how well the kidneys are filtering the blood. It is calculated from a blood creatinine level together with age and sex, and reported in mL/min/1.73 m² – the volume of blood plasma cleared each minute, scaled to an average adult body surface area. A healthy young adult typically has an eGFR above 90; values below 60 for three months or more indicate chronic kidney disease (CKD).

The calculator above uses the CKD-EPI 2021 creatinine equation, recommended in the United States since 2021 and used by most US laboratories. It accepts creatinine in mg/dL or µmol/L and shows the KDIGO GFR category (G1–G5) with an explanation. For example, a 65-year-old woman with a creatinine of 1.2 mg/dL (106 µmol/L) has an eGFR of about 50 – category G3a.

This guide explains what GFR is, how the equation works, how to read the stages, why the race coefficient was removed, when eGFR is unreliable, and what to do with your result.

What GFR measures

Each kidney contains about a million nephrons, the units that filter blood and make urine. Each nephron begins with a glomerulus, a tiny tuft of capillaries that filters water and small molecules from the blood while keeping blood cells and most proteins inside. The glomerular filtration rate is the total volume of fluid filtered by all glomeruli per minute. In healthy young adults it is about 120 mL/min/1.73 m², meaning the kidneys filter roughly 170–180 liters of plasma a day, almost all of which is reabsorbed.

GFR falls gradually with age, by around 1 mL/min/1.73 m² per year after the age of about 40 in many people, although the rate varies widely. It falls faster with diabetes, high blood pressure, glomerular diseases, inherited kidney disease and other conditions.

Measured versus estimated GFR

Measuring GFR directly requires an injected marker, such as iohexol or iothalamate, and timed blood or urine samples – accurate but impractical for routine care. Instead, GFR is estimated from substances that are filtered by the kidneys and accumulate in the blood when filtration falls. Creatinine, produced from muscle, is the most widely used; cystatin C, produced by all nucleated cells, is an increasingly used alternative.

The CKD-EPI 2021 equation

The equation used in this calculator is:

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^Age × 1.012 [if female]

where:

• Scr is serum creatinine in mg/dL (divide µmol/L by 88.4 first)
• κ is 0.7 for females and 0.9 for males
• α is −0.241 for females and −0.302 for males
• min and max take the smaller or larger of Scr/κ and 1

The equation was developed by the Chronic Kidney Disease Epidemiology Collaboration and published in the New England Journal of Medicine in 2021, using data from about 8,000 participants with measured GFR. It is intended for adults aged 18 and over with stable kidney function.

Worked examples

These values come from the CKD-EPI 2021 equation:

• Man, 50, creatinine 1.0 mg/dL (88 µmol/L): eGFR ≈ 92 – G1.
• Woman, 30, creatinine 0.8 mg/dL (71 µmol/L): eGFR ≈ 102 – G1.
• Man, 40, creatinine 0.9 mg/dL (80 µmol/L): eGFR ≈ 111 – G1.
• Woman, 65, creatinine 1.2 mg/dL (106 µmol/L): eGFR ≈ 50 – G3a.
• Woman, 80, creatinine 1.1 mg/dL (97 µmol/L): eGFR ≈ 51 – G3a.
• Man, 70, creatinine 2.0 mg/dL (177 µmol/L): eGFR ≈ 35 – G3b.

Notice that a creatinine of 1.1–1.2 mg/dL, which falls within many laboratories' "normal" creatinine range, corresponds to an eGFR around 50 in an older woman. This is precisely why laboratories report eGFR rather than relying on creatinine alone.

A short history of GFR equations

The first widely used bedside estimate was the Cockcroft-Gault formula (1976), which estimated creatinine clearance from creatinine, age, weight and sex. In 1999 the MDRD study equation introduced estimates normalised to 1.73 m², and laboratories began reporting eGFR automatically in the 2000s. Because MDRD underestimated GFR at higher levels, the CKD-EPI 2009 equation replaced it in most guidelines, followed by the race-free CKD-EPI 2021 equation. In Europe, the EKFC (European Kidney Function Consortium) equation, published in 2021, is also used in some laboratories and can be applied across ages from childhood. Different equations give somewhat different numbers, so it is best to follow trends from the same laboratory.

Understanding the GFR categories

KDIGO (Kidney Disease: Improving Global Outcomes) classifies GFR into six categories:

What counts as chronic kidney disease

CKD is defined as abnormalities of kidney structure or function present for more than three months. This means either:

• an eGFR below 60 (categories G3a–G5) for more than three months, or
• markers of kidney damage at any eGFR – most commonly albuminuria (a urine albumin-to-creatinine ratio of 30 mg/g or 3 mg/mmol or more), but also blood in the urine of kidney origin, structural abnormalities on imaging, abnormal biopsy findings or a kidney transplant.

An eGFR of 60–89 (G2) on its own, without other markers of kidney damage, does not meet the definition of CKD – it is common in older adults.

Combining eGFR and albuminuria

KDIGO stages CKD by both GFR category and albuminuria category (A1–A3). A person with eGFR 50 and UACR 400 mg/g (G3a A3) has a much higher risk of kidney failure and heart disease than a person with eGFR 50 and UACR 10 mg/g (G3a A1). That is why a urine albumin test is recommended alongside eGFR – see our UACR converter for the categories.

Why race was removed from the equation

Earlier equations – the MDRD study equation (1999) and the 2009 CKD-EPI equation – included a multiplier that increased eGFR for people identified as Black (by 21% and 16%, respectively), based on observations that, on average, Black participants had higher creatinine for the same measured GFR. This coefficient was criticised because race is a social rather than biological category, because it could delay diagnosis, referral and transplant listing for Black patients, and because it did not apply to people of mixed or other backgrounds.

In 2021, a joint task force of the US National Kidney Foundation and the American Society of Nephrology recommended adopting the refitted CKD-EPI 2021 equations without a race coefficient, and recommended increased use of cystatin C. Most US laboratories have since switched. Outside the US, practice varies: some countries, including the UK, had already advised against applying the race coefficient, and many European laboratories continue to use the 2009 CKD-EPI equation without it.

Compared with the 2009 equation without the race term, the 2021 equation gives slightly higher eGFR values for most people, and compared with the 2009 equation with the race term, it gives lower values for Black people.

When eGFR is less reliable

Creatinine-based eGFR assumes average muscle mass, diet and creatinine handling. It can be misleading when:

• Muscle mass is unusual – very muscular people (eGFR underestimated) or people with low muscle mass, amputations, frailty, paralysis or muscle-wasting conditions (eGFR overestimated).
• Diet is unusual – high meat intake or creatine supplements raise creatinine; vegetarian or vegan diets lower it.
• Kidney function is changing rapidly – in acute kidney injury, creatinine lags behind the true fall in GFR, and eGFR equations should not be used.
• Certain medicines block creatinine secretion – trimethoprim, cimetidine, dolutegravir and others raise creatinine without reducing GFR.
• Pregnancy – GFR increases, and the equations have not been validated.
• Extremes of body size – eGFR is normalised to 1.73 m²; for drug dosing in very large or small people, the actual (non-normalised) GFR may be more relevant.
• Children – adult equations do not apply; paediatric equations such as the CKiD bedside Schwartz equation are used.

Cystatin C and combined equations

When creatinine-based eGFR may be inaccurate, or when a decision depends on a precise value (for example, around the threshold of 60), KDIGO recommends measuring cystatin C and calculating eGFR with the CKD-EPI 2021 creatinine–cystatin C equation, which is more accurate than either marker alone. Cystatin C is less affected by muscle mass and diet, but can be altered by thyroid disease, high-dose corticosteroids, inflammation and obesity.

eGFR normal range by age

There is no single "normal" estimated GFR for everyone: kidney function is highest in young adulthood and declines gradually with age. The National Kidney Foundation publishes average eGFR values by age group:

An eGFR of 90 or above is classed as G1 (normal or high) at any age, and 60–89 as G2 (mildly decreased). A value in the G2 range is not called chronic kidney disease unless there are other markers of kidney damage, such as albumin in the urine. See GFR levels and CKD stages for the full table.

eGFR in older adults

Because GFR falls with age, many people over 70 have an eGFR between 45 and 75 without albuminuria or other signs of kidney damage. Whether this represents disease or normal ageing has been debated, and some nephrologists have proposed age-adapted thresholds. Under current KDIGO definitions, a persistent eGFR below 60 still counts as CKD at any age, but the risk associated with stable G3a without albuminuria in older people is modest. In practice, the trend over time, urine albumin and overall health matter more than a single number. Older adults should still take kidney function into account when taking medicines, because many drug doses depend on it.

Preparing for an eGFR test

No special preparation is usually required, but a few simple steps make results more consistent:

• Avoid eating a large meat-based meal in the 12 hours before the test, as cooked meat can raise creatinine temporarily – NICE advises this.
• Avoid very strenuous exercise the day before.
• If you take creatine supplements, tell the clinician, or stop them for a week or two before testing if advised.
• Stay normally hydrated; dehydration can lower GFR temporarily.
• Tell the clinician about recent illness or new medicines, including trimethoprim, which raises creatinine.

A single abnormal result should be repeated to confirm it before a diagnosis of CKD is made.

eGFR and medicine doses

Many medicines are cleared by the kidneys, and their doses need adjusting when kidney function is reduced. Examples include metformin (not recommended to start below eGFR 45 and to stop below 30), many antibiotics, direct oral anticoagulants, gabapentin, pregabalin, lithium and digoxin. SGLT2 inhibitors, which protect the kidneys, have specific eGFR thresholds for starting and continuing.

Drug labels may use either eGFR or creatinine clearance estimated by the Cockcroft-Gault equation. The two are not identical: Cockcroft-Gault uses body weight and is not normalised to body surface area, and in older or underweight people it often gives lower values than eGFR. Our creatinine clearance calculator provides the Cockcroft-Gault estimate when a drug label requires it.

What to do with your result

• G1–G2 without albuminuria: no CKD. Continue routine checks if you have diabetes, high blood pressure, heart disease or a family history of kidney disease.
• G3a: repeat the test within three months to confirm, check a urine albumin-to-creatinine ratio, review medicines, and manage blood pressure and cardiovascular risk. Many people with stable G3a never progress to kidney failure.
• G3b: confirm and monitor more frequently; review medicines carefully; consider referral depending on albuminuria, rate of decline and cause.
• G4: referral to a kidney specialist is usually recommended, with planning for possible future kidney replacement therapy.
• G5: specialist care is essential; a new result in this range needs urgent review.

KDIGO and NICE also recommend referral when eGFR falls quickly – for example, a sustained decrease of 25% or more with a change of category, or a fall of 15 or more within 12 months – or when the predicted five-year risk of kidney failure (using the Kidney Failure Risk Equation) is 5% or higher.

Slowing the decline in kidney function

Treatments that protect kidney function include:

• controlling blood pressure, with ACE inhibitors or angiotensin receptor blockers when albuminuria is present
• SGLT2 inhibitors, recommended for most people with CKD and an eGFR of 20 or more
• good glucose control in diabetes, and for type 2 diabetes with albuminuria, finerenone or a GLP-1 receptor agonist where appropriate
• stopping smoking, keeping active, reducing salt intake and maintaining a healthy weight
• avoiding medicines that can harm the kidneys, such as regular non-steroidal anti-inflammatory drugs (ibuprofen, naproxen), unless advised

When to see a doctor

See a doctor if your eGFR is below 60, if it has fallen noticeably since your last test, or if your urine test shows albumin, even if your eGFR is normal. Seek prompt care if a low eGFR is accompanied by swelling of the legs or face, breathlessness, a marked reduction in urine output, persistent nausea, itching or confusion. People with diabetes, high blood pressure, heart disease or a family history of kidney failure should have eGFR and urine albumin checked at least once a year.