A blood creatinine test is one of the cheapest, most common lab tests in medicine — yet the number on its own tells you surprisingly little. A "normal" creatinine of 1.0 mg/dL means one thing for a 25-year-old competitive athlete with large muscles and quite another for an 80-year-old woman with about 30% less muscle mass. This creatinine calculator turns that single lab value into an estimated glomerular filtration rate (eGFR) using the CKD-EPI 2021 equation — the same race-free formula recommended by the National Kidney Foundation and the American Society of Nephrology — and then maps the result to a chronic kidney disease (CKD) stage so you can see where your kidney function actually stands.
Adjust the four fields and the result card updates instantly: your eGFR in mL/min per 1.73 m², the matching CKD stage, and a plain-English interpretation.
How to Use
- Enter your Serum Creatinine exactly as it appears on your lab report, in mg/dL. Most reports print the unit next to the number; if yours uses µmol/L, divide by 88.4 first to convert (e.g., 88 µmol/L ≈ 1.0 mg/dL).
- Type your Age in years. The equation is built for adults 18 and older; pediatric eGFR uses a different, height-based formula.
- Pick your Sex — female or male. This only changes the two constants in the equation (the κ value and the power α), not your actual result on a personal level.
- Choose Race if your lab report asks for it. Note that the 2021 CKD-EPI equation deliberately does not use race — the field is here only so you can compare this result with older lab printouts that still used the 2009 race-adjusted formula.
- Read the result card: eGFR, the CKD stage code (1 = G1 at/above 90, 2 = G2 60–89, 3 = G3a 45–59, 4 = G3b 30–44, 5 = G4 15–29, 6 = G5 under 15), and the eGFR gap from the normal lower bound of 90 (negative means below normal). An eGFR of 90 or above is the normal range; 60–89 is mildly reduced; below 60 warrants repeat testing over time.
The whole point of the calculator is that creatinine and kidney function are not the same thing. eGFR corrects your raw creatinine for age, sex, and body scale, which is why two people with identical creatinine values can land in very different stages.
The CKD-EPI 2021 Formula
The calculator uses the latest creatinine equation published by Inker and colleagues in 2021, after the nephrology community decided race should not be baked into a clinical estimate:
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(−1.200) × 0.9938^Age × [1.012 if female]
Where:
- Scr is your serum creatinine in mg/dL.
- κ (kappa) is 0.7 for females and 0.9 for males — the roughly "normal" creatinine for each group.
- α (alpha) is −0.241 for females and −0.302 for males.
- 0.9938^Age accounts for the natural decline in filtration as people grow older.
- The 1.012 factor is applied only for females.
Because the equation compares your creatinine to a typical value of your age and sex, a creatinine of 1.2 mg/dL in a 40-year-old man yields about 78 mL/min/1.73 m² (stage G2), while the same creatinine in a 70-year-old man falls to roughly 65 mL/min/1.73 m² — still G2, but clearly trending lower. That age correction is exactly why doctors stopped reading creatinine as a standalone number decades ago.
CKD Stages at a Glance
The result card uses the KDIGO staging thresholds that nephrologists worldwide use:
- G1 — 90 or above: Normal or high filtration.
- G2 — 60 to 89: Mildly reduced function; common with aging.
- G3a — 45 to 59: Mild-to-moderate reduction.
- G3b — 30 to 44: Moderate-to-severe reduction.
- G4 — 15 to 29: Severely reduced function; prepare for possible dialysis planning.
- G5 — below 15: Kidney failure; usually requires renal replacement therapy.
A single eGFR below 60 is not automatically chronic kidney disease — the label "CKD" requires the reduced function (or another marker like protein in urine) to persist for at least three months. That is why doctors usually repeat the test rather than panic over one low value.
Examples
Example 1 — Mild reduction, typical adult. A 54-year-old woman has a creatinine of 0.9 mg/dL. Plugging her into the 2021 equation gives eGFR ≈ 76 mL/min/1.73 m², stage G2 — mildly reduced. This is not alarming: her value sits in the range millions of otherwise healthy middle-aged adults carry, and the calculator's interpretation recommends repeating the test in 6–12 months and checking for urine protein.
Example 2 — Healthy young adult. A 30-year-old female marathon runner with a creatinine of 0.6 mg/dL gets eGFR ≈ 124 mL/min/1.73 m², stage G1 — normal or high. Notice her raw creatinine is low because of low body weight, and the equation correctly translates that into excellent filtration rather than a false scare.
Example 3 — Advanced impairment. A 70-year-old man with long-standing diabetes has a creatinine of 3.5 mg/dL. The equation returns eGFR ≈ 18 mL/min/1.73 m², which the stage code reports as 5 — that numeric code corresponds to KDIGO G4 — severely reduced (the code sequence is 1=G1, 2=G2, 3=G3a, 4=G3b, 5=G4, 6=G5, so code 5 is not "G5"). At this level the interpretation card urges a nephrology referral, since patients in G4 are usually preparing for dialysis access planning within the next one to three years.
Example 4 — Young male at the boundary. A 40-year-old man with creatinine 1.2 mg/dL lands at eGFR ≈ 78 mL/min/1.73 m², stage G2 — technically "mildly reduced," but within the variation seen in healthy adults his age.
FAQ
What is a normal creatinine level?
For adults, serum creatinine is usually reported between about 0.6 and 1.3 mg/dL, with men typically running higher than women because of greater muscle mass. But "normal" depends heavily on age: a value of 1.3 mg/dL may be perfect for a muscular 30-year-old man yet mildly concerning for a frail 80-year-old woman. That is exactly why the calculator converts creatinine to eGFR rather than judging the raw number.
What is the difference between creatinine and eGFR?
Creatinine is a waste molecule your muscles produce every day; the lab measures its concentration in your blood. eGFR is an estimate of how well your kidneys filter, calculated from creatinine plus your age and sex (and, in older equations, race). Two people with the same creatinine can have different eGFRs — the younger, more muscular person filters faster.
How is eGFR calculated?
This calculator uses the CKD-EPI 2021 equation: eGFR = 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^(−1.200) × 0.9938^Age, times 1.012 if you are female. κ is 0.7 (female) or 0.9 (male), and α is −0.241 (female) or −0.302 (male). It is the most widely validated adult equation in use today.
What CKD stage is an eGFR of 60?
An eGFR of 60–89 is stage G2 (mildly reduced), and 90 or above is G1. Below 60 you enter the G3 range: 45–59 is G3a and 30–44 is G3b. Stages G4 (15–29) and G5 (under 15) indicate severe impairment or kidney failure. Remember that chronic kidney disease requires the abnormality to persist for about three months, so a single low value is usually repeated before a diagnosis is made.
Why does the race field not change my result?
Until 2021, the CKD-EPI equation included a Black-race multiplier of 1.159, which inflated eGFR estimates for Black patients and could delay care. Following a 2021 National Kidney Foundation / American Society of Nephrology task force report, the race-free 2021 equation removed that term entirely. The calculator keeps the race selector purely so you can compare its output with older lab reports.
What do the CKD stage numbers mean?
The result card prints a numeric code that maps directly to the KDIGO stages: 1 = G1 (eGFR at/above 90, normal or high filtration), 2 = G2 (60–89, mildly reduced), 3 = G3a (45–59, mild-to-moderate), 4 = G3b (30–44, moderate-to-severe), 5 = G4 (15–29, severe reduction), and 6 = G5 (below 15, kidney failure). The companion "eGFR below 90" field shows how many mL/min/1.73 m² you sit under the normal lower bound — a negative number means reduced filtration, while a positive number means you are above the normal floor.
What can raise my creatinine?
High creatinine (and therefore lower eGFR) can come from genuine kidney damage — diabetes, hypertension, glomerulonephritis — but also from non-kidney causes such as dehydration, intense exercise, a high-protein meal, creatine supplements, certain antibiotics, or a large recent muscle mass. If your value is mildly elevated, drinking normally and repeating the test while rested often resolves it.
Should I worry about a creatinine of 1.2 mg/dL?
Usually not by itself. A 40-year-old man with 1.2 mg/dL calculates to roughly 78 mL/min/1.73 m² — stage G2, within normal age-related variation. Worry is warranted only when eGFR falls below 60 persistently, when urine shows protein or blood, or when creatinine climbs compared with a previous test. Always discuss trends with your own doctor.
Disclaimer
This creatinine calculator is provided for informational purposes only and is not medical advice, diagnosis, or treatment. It applies the CKD-EPI 2021 equation to the numbers you enter and should not replace interpretation by a qualified clinician. eGFR estimates are less reliable in people with unusual muscle mass, amputees, pregnant people, children, or those on very high-protein diets. Kidney disease is diagnosed from repeated tests, urine studies, and clinical context — always consult your physician about your lab results before making any health decision.