eGFR Calculator (CKD-EPI 2021)
Estimate how well your kidneys filter blood from a creatinine result, a cystatin C result or both, using the race-free CKD-EPI equations the National Kidney Foundation recommends.
What eGFR tells you
eGFR estimates how much blood your kidneys filter each minute, scaled to a standard body size and reported in ml/min/1.73 m². It is calculated from a blood marker, creatinine or cystatin C, plus age and sex.1 The creatinine equation is designed for laboratory creatinine values standardized to the reference method (IDMS), which is how US laboratories report it (National Kidney Foundation).
Why the 2021 equations dropped race
Earlier equations included race. In 2021 the CKD-EPI researchers built new equations without it, noting that race in eGFR equations is a social rather than a biological construct. They used 10 studies with 8,254 participants for the creatinine equation and 13 studies with 5,352 participants for the combined creatinine and cystatin C equation, then checked the results in 12 further studies with 4,050 participants.1 The new equations that use both creatinine and cystatin C were the most accurate and narrowed the differences between Black and non-Black participants.1
Creatinine, cystatin C or both
When both results are available, the combined equation is the better estimate: in the 2012 validation, it was more precise than either marker alone (an interquartile range of error of 13.4 ml/min/1.73 m², against 15.4 and 16.4).2 That is why this calculator labels the combined result as the main estimate when you enter both. NIDDK notes that the 2021 creatinine-only equation can be less precise than the equations that use cystatin C, overestimating measured GFR by about 4% on average in non-Black people and underestimating it by about 4% in Black people (NIDDK).
What the number means
A large international analysis of 45 cohorts with 1,555,332 participants supported keeping the definition of chronic kidney disease as an eGFR below 60 ml/min/1.73 m² or a urine albumin-to-creatinine ratio above 30 mg/g.3 One reading is not a diagnosis, and a normal eGFR does not rule out kidney disease if urine albumin is raised, so your clinician will look at repeat results and a urine test together.
Kidney function and age
Kidneys age by steadily losing nephrons, with a matching fall in GFR that begins around age 30. In older adults, a modest, persistent reduction to about 45 to 59 ml/min/1.73 m² without abnormal protein in the urine does not seem to carry much added risk to survival.4
How we check this calculator
The page uses the published equations exactly as the National Kidney Foundation lists them. Every time the site is built, an automated test compares our code with an independent implementation of the same equations across 220 combinations of age, sex and lab values; the build fails if any result differs.
This calculator is for education. It does not diagnose kidney disease or replace your clinician, who will interpret eGFR alongside urine tests, repeat results and your history. It is not intended for children, pregnancy or rapidly changing kidney function.
References
- 1Inker LA, et al. "New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race." N Engl J Med. 2021;385(19):1737-1749. PubMed · DOI
- 2Inker LA, et al. "Estimating glomerular filtration rate from serum creatinine and cystatin C." N Engl J Med. 2012;367(1):20-9. PubMed · DOI
- 3Levey AS, et al. "The definition, classification, and prognosis of chronic kidney disease: a KDIGO Controversies Conference report." Kidney Int. 2011;80(1):17-28. PubMed · DOI
- 4Glassock R, et al. "When kidneys get old: an essay on nephro-geriatrics." J Bras Nefrol. 2017;39(1):59-64. PubMed · DOI