eGFR Calculator: Kidney Function Estimate (CKD-EPI 2021)

Your lab sheet gives you a creatinine number, not an answer. This eGFR calculator turns that number into an estimated glomerular filtration rate using the CKD-EPI Creatinine (2021) equation, the race-free formula the National Kidney Foundation and the American Society of Nephrology recommend and US labs now report. Enter your age, sex, and serum creatinine in mg/dL or µmol/L, and you get your eGFR in mL/min/1.73m² plus the KDIGO GFR category it falls in. This is an educational estimate only, not medical advice and not a diagnosis. Discuss any result with your clinician.

One name note, because this page used to carry it. This calculator is not affiliated with DaVita, and it is not the DaVita tool. DaVita is a dialysis provider, and its own GFR calculator states that it uses the same public CKD-EPI Creatinine (2021) equation used here, so there is no separate DaVita method or DaVita dataset behind either tool. If you want the provider’s own page, it is the GFR Calculator at davita.com. What you get here instead is the same standard equation with the working shown: the exact formula, a checked worked example, and a side-by-side look at what the older MDRD equation would have made of the same blood test.

Quick Answer

Three numbers that frame any eGFR result

Three thresholds do most of the work in kidney reporting, and knowing them makes any result easier to place. They come from the KDIGO classification that clinicians use worldwide.

The middle number carries a condition people often miss: below 60 matters when it lasts. According to NIDDK guidance on identifying CKD, the diagnosis generally requires evidence for more than 3 months of kidney damage, decreased function (eGFR under 60), or both. A single low reading during an illness, after hard exercise, or while dehydrated is a reason to retest, not a verdict. The prevalence figure is the other framing worth keeping: kidney disease is common and usually silent, which is why a routine creatinine on a lab panel gets converted into an eGFR at all. The CDC’s CKD basics page puts it at more than 1 in 7 American adults, with as many as 9 in 10 of them unaware they have it.

The CKD-EPI 2021 equation, term by term

The equation estimates filtration from creatinine by correcting for the three things that change creatinine without changing kidneys: age, sex, and where a person’s creatinine sits relative to a sex-specific reference point. It was published by Inker and colleagues in the New England Journal of Medicine in 2021 after the NKF-ASN task force work, and NIDDK’s GFR equations guidance supports it as the recommended creatinine equation.

The min and max terms are the part worth understanding. Below the reference point κ, creatinine barely moves the result, because small creatinine differences at low levels mostly reflect muscle and diet rather than filtration. Above κ, the −1.200 exponent takes over and every rise in creatinine pulls the estimate down steeply. That split is why a creatinine drifting from 1.0 to 1.3 mg/dL in an older man is a bigger event than the small numbers suggest, and why the same 1.3 means different things at 55 for a man (64.9) and a woman (48.6). The 0.9938^age term applies a small, steady decline for each year of life, reflecting the gradual fall in filtration that happens with age even in healthy kidneys.

Worked example: one creatinine, two answers, and what the old equation said

The worked example is the pre-filled case in the calculator. A 55-year-old man with creatinine 1.3 mg/dL: Scr/κ is 1.3 / 0.9 = 1.444, so the min term is 1 and the max term is 1.444^−1.200. The calculation runs 142 × 1.444^−1.200 × 0.9938⁵⁵ = 64.9 mL/min/1.73m², category G2. Enter 114.9 µmol/L instead of 1.3 mg/dL and you get the same 64.9, because the tool divides by 88.4 before calculating. For a 55-year-old woman with the same creatinine, Scr/κ is 1.3 / 0.7 = 1.857, and 142 × 1.857^−1.200 × 0.9938⁵⁵ × 1.012 = 48.6, category G3a.

Now run the same two people through the older IDMS-traceable MDRD equation (175 × Scr^−1.154 × Age^−0.203 × 0.742 if female), the formula labs used before CKD-EPI:

The gaps are not rounding. For the man, MDRD puts him under the 60 line (57.3) while the current equation puts him above it (64.9). For the woman, MDRD says 42.5 (G3b) where CKD-EPI 2021 says 48.6 (G3a). And MDRD with its Black coefficient applied to the same man returns 69.5, a third answer for one blood test, produced entirely by a race multiplier. If an old printout disagrees with a recent lab report, an equation change is the first explanation to check, before assuming your kidneys changed. NIDDK makes the same point to laboratories: compare trends only across values calculated with the same equation.

KDIGO GFR categories, and the albumin half of the picture

A GFR category describes filtration only, and the full KDIGO picture pairs it with a urine albumin category. The G categories below are the ones this calculator reports, taken from the KDIGO 2024 CKD guideline.

The albumin half comes from a urine albumin-to-creatinine ratio (UACR): A1 is under 30 mg/g (normal to mildly increased), A2 is 30–300 mg/g (moderately increased), and A3 is over 300 mg/g (severely increased). Two people with the same eGFR can sit at very different risk once albumin is counted, which is why NIDDK describes kidney testing as two tests, a blood test for GFR and a urine test for albumin, not one. A UACR of 30 mg/g or more may be a sign of kidney disease even when eGFR is above 60. One more indexing note: the 1.73m² in the unit means the result is scaled to a standard body size so people can be compared fairly. It is not your personal surface area; if you ever need that figure itself, a body surface area calculator works it out from height and weight.

Why older results disagree: MDRD and CKD-EPI 2009

Three equations have carried US kidney reporting, and only the newest belongs on a current lab report. The differences are structural, not cosmetic.

The practical rule is simple. Compare like with like: a 2025 result from the 2021 equation against a 2019 result from MDRD mixes real change with equation change. Ask your clinician which equation produced an older number before reading a trend into it.

eGFR is not creatinine clearance

These two numbers get confused constantly, and they are not interchangeable. eGFR, the number on this page, is indexed to a standard body surface area and reported in mL/min/1.73m², which suits staging and comparison. Creatinine clearance from the Cockcroft-Gault equation is a different estimate: it needs body weight, returns plain mL/min with no surface-area indexing, and survives mainly in drug-dosing references. The National Kidney Foundation lists its Cockcroft-Gault tool for drug research use, which tells you how narrow that role now is. This calculator does not compute creatinine clearance, and you should not type an eGFR into a dosing band written for CrCl, or the reverse, without pharmacy or clinician guidance. When a medication decision rides on the number, KDIGO and the KDOQI statement both point to a confirmatory test, often cystatin C, rather than a second creatinine equation.

When this estimate misleads

Every creatinine equation assumes creatinine is stable and that your muscle mass is roughly typical, and both assumptions fail in recognisable situations. The estimate runs low or high for reasons that have nothing to do with your kidneys when creatinine is still rising or falling during an acute illness, when muscle mass is far from average (bodybuilding, amputation, severe muscle loss, eating disorders), during pregnancy, and after creatine supplements or a large cooked-meat meal, since both raise creatinine directly. Some medicines, including trimethoprim and cimetidine, block creatinine secretion into the urine and raise the blood level without harming filtration. Activity level is part of the same story: sustained training builds the muscle that produces creatinine, a link worth remembering if you track fitness numbers with something like a BMI and walking calculator while also watching kidney labs. In any of these cases the honest next step is not a different online calculator. It is a repeat test when you are well and hydrated, plus a cystatin C based estimate (eGFRcr-cys) if your clinician needs a firmer number, exactly as the KDIGO guideline’s confirmatory pathway sets out.

Five sensible steps after a low result

A low eGFR starts a process; it does not end one. These are the steps kidney organisations describe for turning one number into a reliable picture, to work through with your clinician rather than alone.

1. Repeat the test. CKD requires persistence over 3 months, so a confirmatory repeat when you are well, hydrated, and off creatine supplements separates a real finding from a bad week.
2. Add the urine test. Ask for a urine albumin-to-creatinine ratio if you have not had one. Albumin in the urine (30 mg/g or more) changes both the diagnosis and the risk picture at any eGFR.
3. Bring your medicine list. Blood pressure medicines, diabetes medicines, and painkillers such as NSAIDs all interact with kidney care. Reviewing them is a clinician task; do not stop or adjust prescribed medicines on the strength of a calculator result.
4. Work the two big levers. Diabetes and high blood pressure are the leading causes of kidney failure in the US, accounting for about 2 in 3 new cases according to the CDC. Keeping blood pressure and glucose in the ranges your clinician sets is the main way progression is slowed; a blood pressure percentile calculator can help you see where a reading sits while you track it.
5. Know the referral lines. Persistent eGFR under 60 merits ongoing follow-up, under 30 usually means specialist (nephrology) involvement, and under 15 means planning conversations about dialysis or transplant. Sudden changes, blood in the urine, or swelling deserve prompt care at any number.

What competing calculators miss

The strongest tools for this search are the National Kidney Foundation’s own calculator and DaVita’s, and both run the same CKD-EPI 2021 equation as this page. Where they stop short is explanation: neither shows what your lab value would have scored under the older equations, which is the single most common reason a returning patient lands on a page like this, holding two printouts that disagree. Multi-equation tools such as MiniWebTool go the other way and hand you four numbers at once, including an MDRD result your lab no longer reports, with no clear word on which figure to act on.

This page takes the narrower, more useful path. One current-standard answer, stated plainly. The old equations shown once, as a labelled comparison with checked numbers (64.9 versus 57.3 for the same man), so a discrepancy gets explained instead of multiplied. Both creatinine units accepted, with the conversion visible. And the two cautions that decide whether a category means anything at all, the 3-month persistence rule and the albumin test, stated next to the staging table rather than buried in a disclaimer.

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