eGFR Calculator (CKD-EPI 2021) with Kidney G Stage

How is eGFR calculated?

The CKD-EPI 2021 equation estimates glomerular filtration rate from serum creatinine, age and sex. Creatinine must be in mg/dL, so a value in µmol/L is divided by 88.4 first.

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

Scr is serum creatinine in mg/dL.
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 mean that only one creatinine term changes the result. If Scr/κ is below 1, the α term applies. If it is above 1, the −1.200 term applies.

The result is in mL/min/1.73 m², rounded to a whole number. Unlike the 2009 version, the 2021 equation has no race coefficient.

How to use the eGFR calculator

Enter the Age in years. The equation is validated for adults, 18 and over.
Choose the Sex: Female or Male.
Pick the Creatinine unit that matches the lab report: µmol/L or mg/dL.
Enter the Serum creatinine and read the eGFR and the GFR category (G1 to G5).

The category follows the rounded number you see. An exact value of 59.6 shows as 60 and falls in G2, not G3a.

Worked examples

Example 1 – creatinine in µmol/L. A 68-year-old man, creatinine 130 µmol/L. 130 ÷ 88.4 = 1.471 mg/dL. Scr/κ = 1.471 ÷ 0.9 = 1.634, above 1, so the −1.200 term applies: 1.634^−1.2 = 0.555. Then 0.9938^68 = 0.655. 142 × 0.555 × 0.655 = 52 mL/min/1.73 m², category G3a.

Example 2 – creatinine in mg/dL. A 60-year-old man, creatinine 1.0 mg/dL. Scr/κ = 1.0 ÷ 0.9 = 1.111; 1.111^−1.2 = 0.881. Then 0.9938^60 = 0.689. 142 × 0.881 × 0.689 = 86 mL/min/1.73 m², category G2.

Example 3 – a low creatinine. A 30-year-old woman, creatinine 0.6 mg/dL. Scr/κ = 0.6 ÷ 0.7 = 0.857, below 1, so this time the α term applies: 0.857^−0.241 = 1.038. Then 0.9938^30 = 0.830. 142 × 1.038 × 0.830 × 1.012 = 124 mL/min/1.73 m², category G1.

GFR categories (KDIGO)

Category	eGFR (mL/min/1.73 m²)	Description
G1	90 or more	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	below 15	Kidney failure

G1 and G2 count as chronic kidney disease only when there are other signs of kidney damage, such as albuminuria. KDIGO stages CKD by both the G category and the albuminuria (A) category.

Common mistakes

Wrong creatinine unit. 80 µmol/L entered as 80 mg/dL gives an eGFR close to zero. The reverse, 0.9 mg/dL entered as µmol/L, gives an absurdly high value. A normal adult creatinine is roughly 45–110 µmol/L, or 0.5–1.2 mg/dL.
Comparing different equations. CKD-EPI 2009, MDRD and CKD-EPI 2021 give different numbers for the same blood test. Trends are best followed within the same equation.
Reading one value as a diagnosis. Creatinine varies day to day. A single eGFR is a snapshot, not a label.
Using eGFR as if it were CrCl. Drug labels that dose on Cockcroft-Gault expect that calculation, in mL/min and not indexed to body surface area. Use the creatinine clearance calculator for those, and see our guide to eGFR vs creatinine clearance for when each applies.

When the estimate is unreliable

Changing kidney function. In acute kidney injury creatinine lags behind the true GFR, so the equation is only valid when creatinine is stable.
Unusual muscle mass. Amputation, paralysis, frailty and malnutrition lower creatinine production and make eGFR look better than it is. Very high muscle mass or creatine supplements do the opposite.
Body size far from average. For a very small or very large person the indexed value can mislead. The absolute GFR is eGFR × BSA ÷ 1.73, and the body surface area calculator gives the BSA.
Children, pregnancy and dialysis. The equation was not developed for these groups.
Drugs that block creatinine secretion, such as trimethoprim, can raise creatinine without a change in true GFR.

In these situations a cystatin C–based estimate or a measured clearance is often used instead.

Frequently asked questions

Which equation does this eGFR calculator use?

The CKD-EPI 2021 creatinine equation, published by Inker and colleagues in 2021. It is the race-free update of the 2009 equation, so there is no ethnicity input. It needs only serum creatinine, age and sex, and the result is indexed to 1.73 m² of body surface area.

Why is the result in mL/min/1.73 m²?

Because eGFR is indexed to a standard body surface area of 1.73 m². This lets you compare kidney function between people of different sizes. It is not the absolute filtration rate of the person in front of you: for that, multiply eGFR by the person’s BSA and divide by 1.73.

Can I enter creatinine in µmol/L or mg/dL?

Yes, either. Choose the Creatinine unit that matches the lab report and enter the number as it is. For µmol/L the calculator divides by 88.4 to convert to mg/dL before applying the equation, and shows that step. Italian labs usually report mg/dL, UK labs µmol/L.

Why is my result different from the eGFR on the lab report?

Usually because the lab uses another equation or rounds differently. In Europe the EFLM recommends that laboratories keep CKD-EPI 2009; some still use MDRD, and some report only “above 90” or “above 60”. For the same creatinine, CKD-EPI 2021 usually gives a few points more than 2009. It’s worth checking which equation your lab uses before comparing, and following trends only within the same equation.

Does a low eGFR mean the person has chronic kidney disease?

Not on its own. CKD is defined by a reduced GFR, or other markers of kidney damage, lasting more than three months. Staging also uses albuminuria, not only the G category. A single eGFR is a snapshot, and creatinine can change from one day to the next.

Can I use eGFR to adjust drug doses?

It depends on the drug. Some product information uses eGFR, and some uses creatinine clearance from Cockcroft-Gault. It’s best to use the measure named in the product information or local guidance, because the two are not interchangeable. Our guide on eGFR versus creatinine clearance explains when each one applies.

eGFR calculator (CKD-EPI 2021)