Kidney Function Calculator — eGFR

Use the kidney function calculator (eGFR)

Enter age, sex, and creatinine to estimate eGFR and CKD stage. Add ACR for albuminuria context and optional BSA for absolute GFR.

How to Use Kidney Function Calculator — eGFR

1. Step 1: Enter age and select sex

   Type your age in years (18–120) and choose sex. The CKD‑EPI 2021 equation adjusts for these inputs.

2. Step 2: Add creatinine and pick units

   Enter serum creatinine and select mg/dL or µmol/L. Switching units converts the same value automatically.

3. Step 3: Optional: ACR and body size

   Toggle ACR (mg/g) to see albuminuria context. Enable BSA to view absolute GFR (mL/min).

4. Step 4: Calculate kidney function

   Tap Calculate to see eGFR (mL/min/1.73 m²), CKD stage (G1–G5), and any ACR‑based risk label.

5. Step 5: Review and compare

   Use the Understanding section and Related Calculators to interpret values and explore next steps.

Key Features

• CKD‑EPI 2021 eGFR (no race)
• CKD staging (G1–G5) + ACR context
• Creatinine in mg/dL or µmol/L
• Optional absolute GFR via BSA
• Mobile‑first inputs, clear results

Understanding Results

Formula

This tool uses the CKD‑EPI 2021 creatinine equation. In simple terms, it compares your serum creatinine (Scr) to a sex‑specific reference value (κ is 0.7 for females and 0.9 for males), applies two power terms for values below/above that reference, and adjusts for age. A small factor is applied for females. The result is standardized per 1.73 m² of body surface area and reported as mL/min/1.73 m².

Interpreting kidney function calculator results

CKD stages based on eGFR are commonly grouped as follows: G1 ≥ 90 (normal/high when no kidney damage), G2 60–89 (mildly decreased), G3a 45–59, G3b 30–44, G4 15–29, and G5 < 15 mL/min/1.73 m². To refine risk, clinicians also look at albuminuria with categories A1 (< 30 mg/g), A2 (30–300 mg/g), and A3 (> 300 mg/g). Persistent changes over time matter more than a single result; repeat testing and context (blood pressure, diabetes, imaging, medications) are essential.

Assumptions & Limitations

eGFR is an estimate based on population data; it is less reliable in pregnancy, acute illness, extremes of muscle mass, and some medication or diet conditions. If the result seems out of step with how you feel or with prior labs, discuss it with your clinician—cystatin C or measured clearance may add clarity.

Complete Guide: Kidney Function Calculator — eGFR

Estimate kidney function with our kidney function calculator. Enter age, sex, and creatinine (mg/dL or µmol/L) to get eGFR, CKD stage, and ACR context.

The goal of this kidney function calculator — egfr is practical: make it fast to estimate kidney filtration, and just as fast to read the number in context—CKD staging, albuminuria, and everyday factors that shape accuracy. This guide walks through the formula used, typical ranges, and how small choices like units or hydration can influence your result.

What “kidney function” means

In everyday language, kidney function describes how effectively your kidneys filter waste, balance fluids, and regulate electrolytes. Because directly measuring filtration is complex, clinicians use estimates based on routine blood and urine tests. The most common estimate is eGFR (estimated glomerular filtration rate), calculated from serum creatinine, age, and sex. To round out the picture, a urine test—albumin‑to‑creatinine ratio (ACR)—shows whether there is excess protein in the urine, which can signal kidney damage even when the filtration number is near normal.

Your kidneys are resilient. One isolated result rarely tells the whole story. Evidence of chronic kidney disease (CKD) generally requires changes that persist for at least three months, considered alongside risk factors (blood pressure, diabetes, medications), imaging, and symptoms. The kidney function calculator — egfrhelps you place a single snapshot in context and plan informed conversations with your clinician.

How to read eGFR at a glance

eGFR roughly corresponds to kidney filtering capacity. Higher numbers indicate better filtration; persistent values below 60 mL/min/1.73 m² generally prompt closer follow‑up, especially with albumin in the urine (elevated ACR). A single low value during illness or dehydration may rebound on repeat testing. Use the kidney function calculator for a quick estimate, then pair it with ACR, blood pressure logs, and your lab’s reference notes.

Bottom line: treat one reading as a starting point, not a verdict. Repeat the test when you’re well, compare with prior results, and bring the full picture (medications, blood pressure, ACR) to your clinician. The trend across months tells the real story.

Formula and inputs used

The calculator uses the CKD‑EPI 2021 creatinine equation, which estimates eGFR without a race coefficient. In plain terms, the math compares your creatinine to a sex‑specific reference value (κ) and then applies two power terms to handle values below and above that reference. A small age factor decreases the estimate each year. The equation is standardized to a body surface area of 1.73 m², so results are reported in mL/min/1.73 m².

Required inputs are minimal: age (adults only), sex, and serum creatinine. You can enter creatinine in mg/dL or µmol/L and switch units at any time—the number is converted for you. If you want to see how body size would change the absolute filtration rate, enable the BSA option to show an additional value in mL/min using the Mosteller body surface area adjustment.

Creatinine units and conversion

Labs report creatinine in either mg/dL (common in the United States) or µmol/L (common internationally). The calculator accepts both and keeps your quantity the same when you switch. For reference, 1 mg/dL ≈ 88.4 µmol/L. Enter the units exactly as shown on your lab report to avoid confusion.

Creatinine reflects muscle metabolism, so it can vary with exercise, diet (especially recent meat intake), and muscle mass. This is why two people with the same creatinine may have different eGFR values once age and sex are accounted for. The equation compresses these factors into a practical estimate that tracks reasonably well with measured filtration for most adults.

CKD staging and ACR categories

eGFR is commonly grouped into CKD stages: G1 (≥ 90), G2 (60–89), G3a (45–59), G3b (30–44), G4 (15–29), and G5 (< 15 mL/min/1.73 m²). On its own, eGFR highlights filtration, but CKD classification also weighs albuminuria—how much protein appears in urine. Albuminuria categories are A1 (< 30 mg/g), A2 (30–300 mg/g), and A3 (> 300 mg/g). You can optionally enter your ACR in the calculator to see this context and a combined KDIGO‑style risk label.

Why does albuminuria matter? Because protein in the urine can signify kidney damage even when filtration looks near normal. A person with eGFR in the G1 range but ACR in the A3 range may warrant closer follow‑up than a person with G1 and A1. By pairing G (filtration) and A (albuminuria), risk moves from Low → Moderate → High → Very High across a standard grid. The calculator displays this combined context whenever you enter ACR.

eGFR vs. creatinine clearance

eGFR is a standardized estimate (per 1.73 m² body surface area). Creatinine clearance (CrCl), often estimated by Cockcroft–Gault, approximates the volume of plasma cleared of creatinine per minute without indexing to body size. Some medication labels still reference CrCl for dosing decisions. When doses hinge on kidney function and numbers are borderline or unexpected, clinicians may compare eGFR and CrCl or order a measured clearance test.

If you need a CrCl estimate, try our dedicated creatinine clearance calculator. For a focused eGFR workflow, the eGFR calculator offers the same CKD‑EPI 2021 approach with an option to view absolute (BSA‑adjusted) values.

What can affect accuracy

Estimates perform best when labs are stable and typical. Certain scenarios deserve extra caution or alternate methods:

• Rapidly changing kidney function (acute illness or injury) where creatinine is not at steady state.
• Extremes of muscle mass, recent intense exercise, or high meat intake that alter creatinine independent of filtration.
• Pregnancy, severe liver disease, and some medications or supplements that influence creatinine production or assay.
• Pediatric use—children require different equations; this tool is intended for adults.

Hydration can also shift creatinine slightly. If a result seems off compared to how you feel or compared to prior labs, repeating the test under usual conditions—ordinary diet, normal activity, well rested—often clarifies the picture. When estimates and the clinical picture disagree, clinicians may check cystatin C or proceed to measured clearance when precision matters.

Preparing for labs and when to repeat

You do not need elaborate preparation for creatinine testing. A few practical tips help reduce noise: avoid unusually heavy workouts just before the blood draw, follow your usual diet (rather than a very high‑meat meal immediately before testing), and bring a list of medications and supplements. If you track blood pressure at home, consider recording a few readings to discuss the full context.

If your number is new or unexpected, a repeat test is common. Chronic kidney disease is defined by persistent changes, so clinicians generally confirm that an abnormal result remains present over time. The interval varies—days to weeks for clarifying a lab quirk, months for routine monitoring—based on individual risk factors.

What to do next

Use your kidney function calculator — egfr result as a conversation starter. If the estimate is lower than expected or changes from prior labs, bring it to your clinician along with medications, supplements, and home measurements (blood pressure, weight, glucose). To review blood pressure context, try our blood pressure calculator. For metabolic context, our A1C calculator converts A1C ↔ eAG, and the hydration calculator offers a practical daily fluid target. If you want to consider body size in dosing or physiology discussions, calculate body surface area.

Tracking eGFR trends over time

One number rarely tells the story. Kidney function is best understood as a trend over months. Consider saving results from the same lab to reduce noise from method differences, and try to keep pre‑test routines consistent (hydration, exercise timing, and large meat meals can nudge creatinine). If your eGFR dips once and returns to baseline on repeat testing, clinicians often view that differently than a steady downward drift across several measurements. For people with diabetes, blood pressure readings and ACR add helpful context — a stable eGFR with rising albuminuria may still warrant attention. If your care team changes medications (for example, starting an ACE inhibitor/ARB or an SGLT2 inhibitor), they may expect a small initial shift with longer‑term kidney protection; documenting values before and after helps you interpret those changes confidently. Bring a short log of dates and results to appointments — it keeps conversations focused on what has changed and what actions make sense next.

If a medication label references creatinine clearance rather than eGFR, use the creatinine clearance calculator to estimate Cockcroft–Gault. For a focused eGFR‑only workflow, the dedicated eGFR calculator mirrors the same equation with a streamlined layout.

Helpful related calculators

• eGFR (CKD‑EPI 2021) — quick estimate of filtration with CKD staging.
• Creatinine clearance (CrCl) — commonly used for medication dosing.
• Blood pressure — hypertension context for kidney health.
• A1C ↔ eAG — glucose perspective when diabetes is part of the picture.
• Hydration — simple daily fluid target estimate.
• BSA — compare indexed vs. absolute GFR using body surface area.

References

Patient‑friendly background and clinical references:

• National Kidney Foundation: GFR
• NCBI Bookshelf: Chronic Kidney Disease (overview)

This article is informational and does not provide medical advice. Always discuss lab results and treatment decisions with your clinician.

Frequently Asked Questions