eGFR Calculator — Estimate Kidney Function (CKD-EPI 2021)
Estimate your glomerular filtration rate (eGFR) from a serum creatinine lab value. Uses the race-free CKD-EPI 2021 equation — the current clinical standard for staging chronic kidney disease.
Serum creatinine (SCr) comes from a blood test — look for "Creatinine" or "Creat" on a basic or comprehensive metabolic panel (BMP/CMP). Typical reference ranges: men 0.74–1.35 mg/dL, women 0.59–1.04 mg/dL.
Mildly reduced kidney function. Often no symptoms. This stage alone is not diagnostic for CKD without other evidence of kidney damage.
| Stage | eGFR | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high |
| G2← You | 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 |
This eGFR is an estimate calculated from serum creatinine using the CKD-EPI 2021 equation. A single eGFR value does not diagnose CKD — diagnosis requires persistent abnormalities over 3+ months and consideration of other markers (urine albumin, imaging, symptoms). Muscle mass, diet, hydration, and medications all affect creatinine. Always discuss your kidney function results with a physician or nephrologist.
How to use this calculator
Enter your sex, age, and serum creatinine value from a recent blood test. Serum creatinine (SCr) is a standard component of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). Your eGFR and CKD stage appear instantly. If you do not have a lab result, ask your doctor — eGFR is routinely reported on any creatinine blood draw.
Understanding your eGFR result
eGFR (estimated glomerular filtration rate) measures how well your kidneys are filtering blood, expressed in mL of blood plasma cleared per minute per 1.73 m² of body surface area. A single eGFR reading is informative but not diagnostic — CKD is defined as persistently abnormal eGFR or other kidney damage markers for more than 3 months. Always discuss your results with a physician who can interpret them in the context of your full clinical picture, including urine albumin, blood pressure, imaging, and medical history.
Frequently asked questions
CKD stages and eGFR ranges
The KDIGO (Kidney Disease: Improving Global Outcomes) classification system defines six GFR categories (G1–G5, with G3 split into G3a and G3b). CKD is defined as abnormalities in kidney structure or function persisting for more than 3 months — eGFR alone does not diagnose CKD, but it is the primary staging tool.
| Stage | eGFR (mL/min/1.73m²) | Description | Typical management approach |
|---|---|---|---|
| G1 | ≥ 90 | Normal or high (with evidence of kidney damage) | Treat underlying condition; annual eGFR/urine monitoring |
| G2 | 60–89 | Mildly decreased | BP control; lifestyle changes; yearly monitoring |
| G3a | 45–59 | Mildly to moderately decreased | Nephrology referral; medication review; dietary guidance |
| G3b | 30–44 | Moderately to severely decreased | Active nephrology management; complication treatment |
| G4 | 15–29 | Severely decreased | Renal replacement therapy planning; intensive management |
| G5 | < 15 | Kidney failure | Dialysis or transplant; or conservative/palliative care |
What eGFR actually measures
Glomerular filtration rate (GFR) is the volume of fluid the kidneys filter from the blood per minute. The "estimated" GFR (eGFR) is calculated from serum creatinine — a waste product of muscle metabolism that healthy kidneys continuously clear from the blood.
- ·Creatinine is produced at a relatively constant rate and freely filtered by the kidney glomeruli — making it a reliable proxy for filtration rate
- ·eGFR is normalized to a standard body surface area of 1.73 m² so results are comparable across body sizes
- ·A value of 100 mL/min/1.73m² means your kidneys are filtering approximately 100 mL of blood plasma per minute
- ·eGFR naturally declines with age: the average 80-year-old has an eGFR of 60–70 even with healthy kidneys
- ·eGFR reflects the combined function of both kidneys — a single remaining kidney typically compensates to roughly 75% of two-kidney function
Factors that affect eGFR readings
Because eGFR is derived from serum creatinine, anything that changes creatinine production or clearance can shift your eGFR without reflecting a true change in kidney function.
- ·Muscle mass: athletes and bodybuilders naturally produce more creatinine, yielding lower eGFR estimates; frail or sarcopenic individuals produce less, yielding higher estimates
- ·Meat consumption: a large steak can transiently raise serum creatinine for several hours — tests are typically done fasting or after avoiding meat
- ·Hydration: severe dehydration concentrates creatinine and lowers eGFR; adequate hydration normalizes it
- ·Medications: NSAIDs (ibuprofen, naproxen), ACE inhibitors, ARBs, and contrast dyes can acutely reduce eGFR
- ·Acute illness: infections, fever, and surgery can temporarily impair kidney filtration without representing chronic disease
- ·Lab variation: eGFR can vary ±5–10% between draws on the same day — trends over multiple tests matter more than any single value
- ·Pregnancy: GFR increases 40–65% during pregnancy, making standard eGFR thresholds unreliable in pregnant patients
CKD-EPI 2021 vs the older MDRD formula
The CKD-EPI 2021 equation (used in this calculator) replaced the MDRD formula as the standard for estimating GFR. It performs better across the full range of kidney function, particularly at higher eGFR values where MDRD systematically underestimates true GFR.
| Feature | MDRD (1999) | CKD-EPI 2009 | CKD-EPI 2021 |
|---|---|---|---|
| Still uses race? | Yes | Yes | No — race removed |
| Accuracy at eGFR ≥ 60 | Underestimates | Better | Best |
| Accuracy at eGFR < 60 | Acceptable | Good | Good |
| Population validated on | CKD patients only | CKD + healthy | Large diverse cohort |
| Current guideline status | Phased out | Largely replaced | Recommended standard (NKF/ASN) |
Normal eGFR by age
eGFR naturally declines with age — approximately 0.75–1 mL/min/1.73m² per year after age 40. This means an eGFR of 68 in a 75-year-old may be within normal aging parameters, while the same value in a 35-year-old would be concerning. Context and trajectory always matter.
| Age group | Average eGFR | Notes |
|---|---|---|
| 20–29 | ~116 | Peak kidney function; high end of normal |
| 30–39 | ~107 | Minimal decline from peak |
| 40–49 | ~99 | Age-related decline begins (~1 mL/min/year) |
| 50–59 | ~93 | Continued gradual decline |
| 60–69 | ~85 | eGFR approaching 60 requires closer monitoring |
| 70–79 | ~75 | G2 range is common and often not pathological |
| 80+ | ~65 | G2/G3a common; CKD staging requires other markers |