What is the 2021 CKD-EPI eGFR formula?

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, κ is 0.7 for women and 0.9 for men, and α is −0.241 for women and −0.302 for men. Those coefficients are printed in Table 2 of Inker et al., N Engl J Med 2021;385:1737–1749. The result is in ml/min/1.73 m². For a 50-year-old man with a creatinine of 1.0 mg/dL it comes to 92.

Does the eGFR equation still use race?

No. The 2009 CKD-EPI creatinine equation multiplied the result by 1.159 for people recorded as Black; the 2021 refit removed that term, and removing it was the purpose of the paper, which states that "race in eGFR equations is a social and not a biologic construct". The NKF-ASN Task Force called for immediate implementation of the race-free equation in all US laboratories in 2021, and KDIGO’s 2024 guideline carries the practice point "Use of race in the computation of eGFR should be avoided". This calculator has no race input because the equation it implements has no race term. Many calculators still online do, and they will give a Black user a figure roughly 16% higher than this page will.

How accurate is eGFR compared with a measured GFR?

In the 2021 validation set of 4,050 people, 87.2% of creatinine-based estimates in Black participants and 86.5% in non-Black participants fell within 30% of measured GFR — which sounds loose because it is: 30% either side of 80 is a range from 56 to 104. Adding cystatin C lifts that to 90.5% and 90.8%. The paper treats 80–90% as acceptable and 90% or better as preferred. Precision is worst at high GFR, so a healthy person’s number should be read as a broad band rather than a reading.

Why is my eGFR low if I lift weights or take creatine?

Because creatinine is a product of muscle metabolism before it is a marker of filtration, and both extra muscle and supplemental creatine raise it without anything happening to your kidneys. KDIGO 2024 lists "Extreme sport/exercise/body builder" and "High-protein diets and creatine supplements" as named indications for measuring cystatin C instead. A meta-analysis of 19 randomised trials put the mean rise on creatine at 0.13 mg/dL, which at a starting creatinine of 1.0 mg/dL in a 35-year-old man moves the reported eGFR from 101 to 87. The same analysis found no significant change in eGFR or urea between creatine and control arms.

Does testosterone therapy affect eGFR?

It affects the creatinine the estimate is built on. KDIGO 2024 lists "Steroids (anabolic, hormone)" in its table of non-GFR determinants of serum creatinine, notes that the effect on cystatin C is "not known", and suggests using the combined creatinine–cystatin C equation in that situation. A 2026 Clinical Journal of the American Society of Nephrology review of gender-affirming hormone therapy states that "Testosterone therapy often raises SCr, while estrogen therapy may lower or has no effect on SCr levels". What none of that establishes is a size of effect for a man on a standard TRT dose — that figure is not something we found a source for, so this page does not state one. If you are on testosterone and your creatinine has risen, the useful next step is a cystatin C, not an assumption in either direction.

What is cystatin C and should I ask for it?

Cystatin C is a small protein produced by nearly all nucleated cells and cleared by the glomerulus, and unlike creatinine its blood level does not track muscle mass. KDIGO’s 2024 Recommendation 1.2.2.1 is to use the combined creatinine–cystatin C estimate "in clinical situations when eGFRcr is less accurate and GFR affects clinical decision-making", and the NKF-ASN Task Force called for national efforts to increase its routine use, "especially to confirm eGFR in adults who are at risk for or have CKD". It is a separate blood test, not part of a basic metabolic panel, and it costs more. If you are muscular, supplementing creatine or on testosterone and a creatinine-based eGFR has come back low, it is the test that actually answers the question.

How do I convert creatinine from µmol/L to mg/dL?

Divide by 88.40 — so 88 µmol/L is 1.0 mg/dL, 106 µmol/L is 1.2 mg/dL and 133 µmol/L is 1.5 mg/dL. Going the other way, multiply. That factor is not arbitrary: creatinine has a relative molecular mass of 113.1179 (C₄H₇N₃O), and 10,000 ÷ 113.1179 = 88.40. Cystatin C needs no conversion; it is reported in mg/L worldwide. The calculator above accepts creatinine in either unit.

Does an eGFR under 60 mean I have chronic kidney disease?

Not by itself. KDIGO defines CKD as a GFR below 60 ml/min/1.73 m² sustained for more than three months, so a single low reading is a reason to repeat the test, not a diagnosis — and readings move with hydration, an acute illness, a hard training session or a recent high-protein meal. Above 60 the bands do not constitute CKD at all on their own: KDIGO’s own footnote says that "in the absence of evidence of kidney damage, neither G1 nor G2 fulfills the criteria for CKD". The usual marker of damage is albuminuria, from a urine albumin-to-creatinine ratio, which is a different test this calculator does not compute.

Is eGFR reliable during an acute illness or acute kidney injury?

No, and this is the failure that catches people out. Every one of these equations assumes creatinine is in steady state — that production and clearance have had time to balance. In acute kidney injury they have not: creatinine lags the loss of filtration by a day or more, so an eGFR calculated in the middle of an acute event describes the kidney of a day ago rather than the one in front of you. KDIGO 2024 lists "non-steady-state conditions" first among the sources of error in creatinine-based estimation. The same applies to any reading taken during a severe illness, a period of dehydration, or shortly after starting or stopping a drug that alters creatinine handling.

Why does the eGFR chart not adjust for my body size?

Because eGFR is reported per 1.73 m² of body-surface area by design — it is a filtration rate for a standard-sized body, which is what makes one person’s number comparable with another’s and with the KDIGO bands. It is not your absolute GFR, and a very large or very small person’s true filtration in ml/min differs from the indexed figure. That distinction matters mainly for dosing some drugs, where an absolute clearance is wanted instead, which is a different calculation from this one and a conversation for whoever is prescribing.

Free clinical tool

eGFR Calculator

Your estimated GFR by the 2021 CKD-EPI equations — the ones with no race coefficient — from serum creatinine in mg/dL or µmol/L, with cystatin C if you have it.

Reviewed by: Alpha Health Finder Editorial Team
Last reviewed: September 2026

What eGFR measures, what changed in 2021, and where creatinine misleads

Glomerular filtration rate is the volume of fluid your kidneys filter out of the blood per minute. Measuring it properly means injecting a marker that the kidneys clear and nothing else touches — iohexol, iothalamate — and sampling blood or urine over several hours. Almost nobody gets that. What appears on a routine panel instead is an estimate calculated from serum creatinine, a waste product of muscle metabolism that the kidneys clear at a roughly predictable rate.

The equation this page uses is the 2021 CKD-EPI creatinine equation. Its inputs are creatinine, age and sex, and that list is the news. The 2009 version it replaced took a fourth input: it multiplied the result by 1.159 when the person was recorded as Black. Inker and colleagues refitted the equation without that term in the New England Journal of Medicine in 2021, stating the reason in the paper's opening line — "race in eGFR equations is a social and not a biologic construct". The NKF-ASN Task Force recommended "immediate implementation of the CKD-EPI creatinine equation refit without the race variable in all laboratories in the United States", and KDIGO's 2024 guideline carries it as a practice point: "Use of race in the computation of eGFR should be avoided."

The change is not free of consequence and the paper does not pretend otherwise. Against measured GFR in the validation set, the 2021 creatinine equation underestimated GFR in Black participants by a median of 3.6 ml/min/1.73 m² and overestimated it in non-Black participants by 3.9. KDIGO 2024 describes the same effect as "a small overestimate of GFR in non-Black individuals and a small underestimate in Black individuals". What the removal bought is a single equation applied to everyone, with agreement within 30% of measured GFR of 87.2% in Black participants and 86.5% in non-Black — for the first time, essentially the same accuracy in both groups. This calculator implements the 2021 equation and nothing else. There is no race question on it because there is no race term in it.

Now the part that matters most if you found this page from a men's health search. Creatinine is a muscle metabolite. The equation assumes your muscle mass and your protein intake are ordinary, and if they are not, the number it returns is wrong in a completely predictable direction: more muscle means more creatinine means a lower eGFR, with no change in your kidneys at all. KDIGO 2024's Table 8, which lists the situations where a creatinine-only estimate should not be trusted, includes "Extreme sport/exercise/body builder", "High-protein diets and creatine supplements" and "Steroids (anabolic, hormone)" among them. A randomised-trial meta-analysis found creatine supplementation raises serum creatinine by a mean of 0.13 mg/dL (95% CI 0.07 to 0.18) while finding no significant change in eGFR or urea, and concluded the rise reflects "metabolic turnover rather than renal impairment". At a starting creatinine of 1 mg/dL in a 35-year-old man, 0.13 mg/dL is the difference between an eGFR of 101 and one of 87.

The answer to that is not to ignore the result. It is to measure cystatin C, a small protein filtered by the glomerulus whose blood level does not track muscle mass. KDIGO 2024's Recommendation 1.2.2.1 is to "use eGFRcr-cys in clinical situations when eGFRcr is less accurate and GFR affects clinical decision-making", and the combined creatinine–cystatin C equation is the most accurate of the three here: 90.5% and 90.8% of its estimates fell within 30% of measured GFR in the two race groups, against 87.2% and 86.5% for creatinine alone. This calculator takes a cystatin C if you have one and solves all three equations at once. If you do not have one, it gives you the creatinine answer and tells you when it is the wrong test to be relying on.

Two limits that apply to everybody. eGFR is expressed per 1.73 m² of body-surface area, so it is a rate for a standard-sized body rather than a measurement of yours — it is not adjusted for your weight and should not be confused with a Cockcroft-Gault creatinine clearance, which is a different quantity used for some drug dosing. And the whole model assumes creatinine is in steady state. In acute kidney injury it is not: creatinine lags the injury by a day or more, so during an acute event the eGFR printed on the report describes a kidney that no longer exists. KDIGO 2024 lists the sources of error in one sentence — "non-steady-state conditions, non-GFR determinants of SCr, measurement error at higher GFR, and interferences with the creatinine assays" — and notes that estimates are least precise at the high end, which is where most healthy readers of this page will land.

The formula

Common form (all three equations):

eGFR = µ × min(Scr/κ,1)^a₁ × max(Scr/κ,1)^a₂

× min(Scys/0.8,1)^b₁ × max(Scys/0.8,1)^b₂

× c^Age × d [if female]

κ = 0.7 female, 0.9 male Scr in mg/dL, Scys in mg/L

2021 CKD-EPI creatinine µ=142 a₁=-0.241/F -0.302/M a₂=-1.200

c=0.9938 d=1.012

2012 CKD-EPI cystatin C µ=133 b₁=-0.499 b₂=-1.328

c=0.996 d=0.932

2021 CKD-EPI creatinine–cys µ=135 a₁=-0.219/F -0.144/M a₂=-0.544

b₁=-0.323 b₂=-0.778

c=0.9961 d=0.963

Units creatinine µmol/L = mg/dL × 88.40

cystatin C mg/L on every report; no conversion

There is a fifth coefficient in the published table — "e, if Black" — and it is the reason the 2021 paper exists. For all three equations above that cell is empty, so there is nothing to implement and nothing here implements it. Each equation is a two-slope power law: below the knot (κ for creatinine, 0.8 mg/L for cystatin C) the curve is shallow, above it steep, which is why a 0.1 mg/dL change matters far more at 1.4 mg/dL than at 0.7. The creatinine exponent above the knot is -1.200 in the creatinine-only equation and only -0.544 in the combined one — the combined equation leans on creatinine roughly half as hard, which is precisely why it is the one to use when creatinine is the input you distrust. The µmol/L factor is derived from the relative molecular mass of creatinine, 113.1179 (C₄H₇N₃O, NIST Chemistry WebBook), not quoted: 10,000 ÷ 113.1179 = 88.403, which rounds to the 88.4 that Inker 2021 prints in its Table 1 footnote. All three equations are for adults; KDIGO 2024 Table 14 gives their age range as 18 and over, and this calculator returns nothing below that rather than extrapolating onto children.

Worked example

A 38-year-old man who lifts four times a week and takes creatine. Serum creatinine 1.35 mg/dL (119 µmol/L) — flagged high by the laboratory. His clinician also ran a cystatin C, which came back 0.85 mg/L:

κ for a man is 0.9, so Scr/κ = 1.35 / 0.9 = 1.500 — above the knot, so the steep exponent -1.200 applies
eGFRcr = 142 × 1.500^-1.200 × 0.9938^38 = 68.9 ml/min/1.73 m²
eGFRcys = 133 × (0.85/0.8)^-1.328 × 0.996^38 = 105.4 ml/min/1.73 m²
eGFRcr-cys, the equation using both markers = 89.0 ml/min/1.73 m²
The creatinine-only figure sits 20 ml/min/1.73 m² below the two-marker one — on one side of 60 to 89 ml/min/1.73 m², where KDIGO's reference table reads "mildly decreased", versus within a rounding error of the top band. Nothing about his kidneys changed between those two numbers; only which molecule was asked about.
This is a constructed panel, not a prediction. A cystatin C can equally well confirm a low creatinine-based figure, and when it does, that is real information rather than a reprieve. The point of running it is that the creatinine answer alone cannot tell you which case you are in.

eGFR chart for men — 2021 CKD-EPI creatinine, by creatinine and age

Find your serum creatinine down the left and your age across the top. The cell is your eGFR in ml/min/1.73 m². Both creatinine units are given on every row.

Serum creatinine	Age 25	Age 35	Age 45	Age 55	Age 65	Age 75
0.6 mg/dL53 µmol/L	137	129	121	114	107	101
0.7 mg/dL62 µmol/L	131	123	116	109	102	96
0.8 mg/dL71 µmol/L	126	118	111	105	98	92
0.9 mg/dL80 µmol/L	122	114	107	101	95	89
1.0 mg/dL88 µmol/L	107	101	95	89	84	78
1.1 mg/dL97 µmol/L	96	90	84	79	74	70
1.2 mg/dL106 µmol/L	86	81	76	71	67	63
1.3 mg/dL115 µmol/L	78	73	69	65	61	57
1.4 mg/dL124 µmol/L	72	67	63	59	56	52
1.6 mg/dL141 µmol/L	61	57	54	51	48	45
1.8 mg/dL159 µmol/L	53	50	47	44	41	39
2.2 mg/dL194 µmol/L	42	39	37	35	32	30
3.0 mg/dL265 µmol/L	29	27	25	24	22	21

Every cell is ml/min/1.73 m², computed by the same function the calculator above calls. There is no race column and there will not be one: the 2021 equation takes creatinine, age and sex, and nothing else. Notice how much steeper the table gets past 0.9 mg/dL — that is the knot in the equation, above which the exponent changes from -0.302 to -1.200. It is also why a small creatinine change matters so much more to men in the middle of this table than at the top of it.

eGFR chart for women — 2021 CKD-EPI creatinine, by creatinine and age

The same equation with the female coefficients. The same creatinine gives a markedly lower eGFR in a woman, because the knot sits lower.

Serum creatinine	Age 25	Age 35	Age 45	Age 55	Age 65	Age 75
0.6 mg/dL53 µmol/L	128	120	113	106	100	94
0.7 mg/dL62 µmol/L	123	116	109	102	96	90
0.8 mg/dL71 µmol/L	105	98	93	87	82	77
0.9 mg/dL80 µmol/L	91	85	80	75	71	67
1.0 mg/dL88 µmol/L	80	75	71	67	63	59
1.1 mg/dL97 µmol/L	72	67	63	59	56	52
1.2 mg/dL106 µmol/L	64	61	57	53	50	47
1.3 mg/dL115 µmol/L	59	55	52	49	46	43
1.4 mg/dL124 µmol/L	54	50	47	44	42	39
1.6 mg/dL141 µmol/L	46	43	40	38	36	33
1.8 mg/dL159 µmol/L	40	37	35	33	31	29
2.2 mg/dL194 µmol/L	31	29	27	26	24	23
3.0 mg/dL265 µmol/L	21	20	19	18	17	16

Sex enters the equation twice: through κ, which is 0.7 mg/dL for women against 0.9 for men, and through a flat ×1.012 multiplier. κ is doing almost all of the work. A creatinine of 1.0 mg/dL is below the knot for a man and well above it for a woman, which is why the same number reads 92 at age 50 in the men's table and 69 here.

What a cystatin C does to the answer

All three equations at one fixed creatinine of 1.35 mg/dL (119 µmol/L) in a 38-year-old man, as the cystatin C varies. The creatinine-only answer is the same 69 in every row.

Cystatin C	eGFRcyscystatin C alone	eGFRcr-cysboth markers	Move from eGFRcrml/min/1.73 m²
0.6 mg/L	132	102	+34
0.7 mg/L	122	97	+29
0.8 mg/L	114	93	+24
0.9 mg/L	98	85	+16
1.0 mg/L	85	78	+10
1.1 mg/L	75	73	+4
1.3 mg/L	60	64	−5
1.6 mg/L	45	54	−14
2.0 mg/L	34	46	−23

This table is the argument for asking for the second test. Holding creatinine completely still, the two-marker answer moves across roughly 57 ml/min/1.73 m² depending on the cystatin C. A low cystatin C alongside a high creatinine is the muscle signature; the two rising together is the one that means something about filtration. Note that the middle column, not the left one, is the number KDIGO recommends: Recommendation 1.2.2.1 asks for eGFRcr-cys, not eGFRcys, "in clinical situations when eGFRcr is less accurate and GFR affects clinical decision-making".

What 0.13 mg/dL of creatinine does to a reported eGFR

The mean rise in serum creatinine on creatine supplementation, from a meta-analysis of randomised trials, applied across a range of starting values in a 40-year-old man. Nothing about the kidney changes between the two columns.

Starting creatinine	eGFR beforeml/min/1.73 m²	eGFR at +0.13 mg/dLml/min/1.73 m²	Changeml/min/1.73 m²
0.8 mg/dL71 µmol/L	115	106	−8
0.9 mg/dL80 µmol/L	111	94	−17
1.0 mg/dL88 µmol/L	98	84	−13
1.1 mg/dL97 µmol/L	87	76	−11
1.2 mg/dL106 µmol/L	78	69	−9
1.3 mg/dL115 µmol/L	71	64	−8
1.5 mg/dL133 µmol/L	60	54	−6
1.8 mg/dL159 µmol/L	48	44	−4

The 0.13 mg/dL is the pooled mean difference (95% CI 0.07 to 0.18) from Tsiaras and colleagues' 2026 meta-analysis of 19 randomised trials. The same analysis found no significant difference in eGFR between creatine and control arms and no difference in urea, and concluded the creatinine rise is "not related to significant alterations in urea concentrations and eGFR" — so this table shows what the arithmetic does, not what creatine does to a kidney. The loss is biggest at the top of the table because that is where the curve is steepest relative to the number. This is also the reason a single eGFR taken during a training block should not be compared with one taken on holiday.

Creatinine unit conversion chart — mg/dL to µmol/L

Creatinine is reported in mg/dL in the US and µmol/L almost everywhere else. Multiply by 88.40 to go one way, divide to go the other. The last two columns show each value's eGFR at age 45.

Serum creatinine	µmol/L	eGFR, manage 45	eGFR, womanage 45
0.6 mg/dL	53	121	113
0.7 mg/dL	62	116	109
0.8 mg/dL	71	111	93
0.9 mg/dL	80	107	80
1.0 mg/dL	88	95	71
1.1 mg/dL	97	84	63
1.2 mg/dL	106	76	57
1.3 mg/dL	115	69	52
1.5 mg/dL	133	58	44
1.8 mg/dL	159	47	35
2.5 mg/dL	221	31	24
4.0 mg/dL	354	18	13

1 mg/dL = 88.403 µmol/L. That factor is not a convention — it is 10,000 divided by 113.1179, the relative molecular mass of creatinine (C₄H₇N₃O) given by the NIST Chemistry WebBook, and it lands on the 88.4 that Inker 2021 prints in its Table 1 footnote. Entering a µmol/L creatinine into a calculator expecting mg/dL is the commonest way this page gets misused: 88 µmol/L is a perfectly ordinary 1.0 mg/dL, but read as 88 mg/dL it is an eGFR the equation would refuse outright. The calculator above takes either unit, so the mistake cannot be made.

When a creatinine-only eGFR is the wrong test — KDIGO 2024, Table 8

The named conditions under which KDIGO says a creatinine-based estimate loses accuracy, and what it suggests instead. The wording in the last three columns is KDIGO’s, reproduced rather than summarised.

Condition	Domain	Cause of decreased accuracy	KDIGO comment on GFR evaluation
Extreme sport/exercise/body builder	Body habitus and changes in muscle mass	Non-GFR determinants of SCr	eGFRcys may be appropriate if an increase in muscle mass is the only abnormality.
High-protein diets and creatine supplements	Diet	Non-GFR determinants of SCr	Minimal data, suggest eGFRcr may be appropriate if no changes to non-GFR determinants of SCr or no comorbid illness.
Steroids (anabolic, hormone)	Medication effects	Non-GFR determinants of SCr. Effect on SCys not known	Physiological effect on SCys unknown, suggest eGFRcr-cys.
Above-knee amputation	Body habitus and changes in muscle mass	Non-GFR determinants of SCr	eGFRcys may be appropriate in those without other comorbid conditions. Suggest eGFRcr-cys in those with comorbid illness.
Class III obesity	Body habitus and changes in muscle mass	Non-GFR determinants of SCr and SCys	eGFRcr-cys demonstrated to be most accurate.
Eating disorders	Body habitus and changes in muscle mass	Non-GFR determinants of SCr	eGFRcys may be appropriate if no comorbid illness other than reduction in muscle mass.

Reproduced from KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease, Kidney Int. 2024;105(4S):S117–S314, Table 8, "Indications for use of cystatin C". This is a subset — the full table also covers smoking, malnutrition, cancer, heart failure, cirrhosis, muscle-wasting disease, spinal cord injury and several medication classes. The rows chosen here are the ones that describe an ordinary gym-going man rather than a rare patient. "SCr" is serum creatinine and "SCys" serum cystatin C. Note what the table does not say: it does not say a creatinine eGFR is meaningless in these people, it says the estimate is less accurate and that a second marker resolves it.

KDIGO GFR categories — a reference, not a diagnosis

The six GFR bands used internationally to describe a filtration rate. Read the footnote before reading yourself into one of them.

Category	eGFRml/min/1.73 m²	KDIGO term
G1	≥90	Normal or high
G2	60–89	Mildly decreased
G3a	45–59	Mildly to moderately decreased
G3b	30–44	Moderately to severely decreased
G4	15–29	Severely decreased
G5	<15	Kidney failure

From KDIGO 2024, Table 2, "GFR categories in CKD". A category is a description of one number on one day; chronic kidney disease is a diagnosis, and the two are not the same thing. KDIGO requires the reduction to persist: the guideline describes "the threshold GFR <60 ml/min per 1.73 m2 (GFR categories G3a–G5) for >3 months to indicate a diagnosis of CKD". Above that line the bands do not constitute CKD at all on their own — Table 2’s own footnote reads "Relative to the young adult level. In the absence of evidence of kidney damage, neither G1 nor G2 fulfills the criteria for CKD", the marker of damage usually being albuminuria on a urine albumin-to-creatinine ratio. KDIGO also notes that estimates are least precise at the high end, which is where most people reading this will be.

Frequently asked questions

What is the 2021 CKD-EPI eGFR formula?: 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, κ is 0.7 for women and 0.9 for men, and α is −0.241 for women and −0.302 for men. Those coefficients are printed in Table 2 of Inker et al., N Engl J Med 2021;385:1737–1749. The result is in ml/min/1.73 m². For a 50-year-old man with a creatinine of 1.0 mg/dL it comes to 92.
Does the eGFR equation still use race?: No. The 2009 CKD-EPI creatinine equation multiplied the result by 1.159 for people recorded as Black; the 2021 refit removed that term, and removing it was the purpose of the paper, which states that "race in eGFR equations is a social and not a biologic construct". The NKF-ASN Task Force called for immediate implementation of the race-free equation in all US laboratories in 2021, and KDIGO’s 2024 guideline carries the practice point "Use of race in the computation of eGFR should be avoided". This calculator has no race input because the equation it implements has no race term. Many calculators still online do, and they will give a Black user a figure roughly 16% higher than this page will.
How accurate is eGFR compared with a measured GFR?: In the 2021 validation set of 4,050 people, 87.2% of creatinine-based estimates in Black participants and 86.5% in non-Black participants fell within 30% of measured GFR — which sounds loose because it is: 30% either side of 80 is a range from 56 to 104. Adding cystatin C lifts that to 90.5% and 90.8%. The paper treats 80–90% as acceptable and 90% or better as preferred. Precision is worst at high GFR, so a healthy person’s number should be read as a broad band rather than a reading.
Why is my eGFR low if I lift weights or take creatine?: Because creatinine is a product of muscle metabolism before it is a marker of filtration, and both extra muscle and supplemental creatine raise it without anything happening to your kidneys. KDIGO 2024 lists "Extreme sport/exercise/body builder" and "High-protein diets and creatine supplements" as named indications for measuring cystatin C instead. A meta-analysis of 19 randomised trials put the mean rise on creatine at 0.13 mg/dL, which at a starting creatinine of 1.0 mg/dL in a 35-year-old man moves the reported eGFR from 101 to 87. The same analysis found no significant change in eGFR or urea between creatine and control arms.
Does testosterone therapy affect eGFR?: It affects the creatinine the estimate is built on. KDIGO 2024 lists "Steroids (anabolic, hormone)" in its table of non-GFR determinants of serum creatinine, notes that the effect on cystatin C is "not known", and suggests using the combined creatinine–cystatin C equation in that situation. A 2026 Clinical Journal of the American Society of Nephrology review of gender-affirming hormone therapy states that "Testosterone therapy often raises SCr, while estrogen therapy may lower or has no effect on SCr levels". What none of that establishes is a size of effect for a man on a standard TRT dose — that figure is not something we found a source for, so this page does not state one. If you are on testosterone and your creatinine has risen, the useful next step is a cystatin C, not an assumption in either direction.
What is cystatin C and should I ask for it?: Cystatin C is a small protein produced by nearly all nucleated cells and cleared by the glomerulus, and unlike creatinine its blood level does not track muscle mass. KDIGO’s 2024 Recommendation 1.2.2.1 is to use the combined creatinine–cystatin C estimate "in clinical situations when eGFRcr is less accurate and GFR affects clinical decision-making", and the NKF-ASN Task Force called for national efforts to increase its routine use, "especially to confirm eGFR in adults who are at risk for or have CKD". It is a separate blood test, not part of a basic metabolic panel, and it costs more. If you are muscular, supplementing creatine or on testosterone and a creatinine-based eGFR has come back low, it is the test that actually answers the question.
How do I convert creatinine from µmol/L to mg/dL?: Divide by 88.40 — so 88 µmol/L is 1.0 mg/dL, 106 µmol/L is 1.2 mg/dL and 133 µmol/L is 1.5 mg/dL. Going the other way, multiply. That factor is not arbitrary: creatinine has a relative molecular mass of 113.1179 (C₄H₇N₃O), and 10,000 ÷ 113.1179 = 88.40. Cystatin C needs no conversion; it is reported in mg/L worldwide. The calculator above accepts creatinine in either unit.
Does an eGFR under 60 mean I have chronic kidney disease?: Not by itself. KDIGO defines CKD as a GFR below 60 ml/min/1.73 m² sustained for more than three months, so a single low reading is a reason to repeat the test, not a diagnosis — and readings move with hydration, an acute illness, a hard training session or a recent high-protein meal. Above 60 the bands do not constitute CKD at all on their own: KDIGO’s own footnote says that "in the absence of evidence of kidney damage, neither G1 nor G2 fulfills the criteria for CKD". The usual marker of damage is albuminuria, from a urine albumin-to-creatinine ratio, which is a different test this calculator does not compute.
Is eGFR reliable during an acute illness or acute kidney injury?: No, and this is the failure that catches people out. Every one of these equations assumes creatinine is in steady state — that production and clearance have had time to balance. In acute kidney injury they have not: creatinine lags the loss of filtration by a day or more, so an eGFR calculated in the middle of an acute event describes the kidney of a day ago rather than the one in front of you. KDIGO 2024 lists "non-steady-state conditions" first among the sources of error in creatinine-based estimation. The same applies to any reading taken during a severe illness, a period of dehydration, or shortly after starting or stopping a drug that alters creatinine handling.
Why does the eGFR chart not adjust for my body size?: Because eGFR is reported per 1.73 m² of body-surface area by design — it is a filtration rate for a standard-sized body, which is what makes one person’s number comparable with another’s and with the KDIGO bands. It is not your absolute GFR, and a very large or very small person’s true filtration in ml/min differs from the indexed figure. That distinction matters mainly for dosing some drugs, where an absolute clearance is wanted instead, which is a different calculation from this one and a conversation for whoever is prescribing.

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Order cystatin C alongside your creatinineCystatin C is not on a basic metabolic panel and has to be asked for. It is the test that separates a muscular man from a man with reduced filtration.What else belongs on a kidney panelA urine albumin-to-creatinine ratio answers a question eGFR cannot, and KDIGO stages kidney disease on both together rather than on filtration alone.

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Educational reference, not medical advice. eGFR is an estimate of filtration calculated from a blood marker, indexed to a standard body size, and validated only when that marker is in steady state. It is unreliable in acute kidney injury, at extremes of muscle mass, after amputation, and on a high-protein diet or creatine supplementation. A single value is not a diagnosis of chronic kidney disease, which requires the reduction to persist beyond three months. Interpretation, and any decision about treatment, belongs to your clinician.