GFR Calculator

A GFR calculator estimates glomerular filtration rate (eGFR), a key marker used in kidney-function assessment. In practice, eGFR is not a direct measured filtration test; it is an estimate derived from serum creatinine and patient variables such as age and sex. Some legacy equations also include race adjustment. This calculator provides adult and pediatric modes so that users can compare common methods in one place.

The adult mode includes CKD-EPI, MDRD, and Mayo Quadratic estimates for comparison. The children mode uses the Schwartz formula, which incorporates height and serum creatinine. Presenting multiple equations helps users understand that eGFR is model-dependent and that values can differ across formulas, especially near decision thresholds.

This tool is educational and supports interpretation literacy, not diagnosis. Clinical decisions require the full context: repeat measurements, urine albumin data, blood pressure, medication history, and physician evaluation.

Adult equations estimate filtration from serum creatinine, but each equation is calibrated differently. CKD-EPI is often preferred in many modern settings because it tends to perform better across broader GFR ranges. MDRD remains historically important and is still seen in legacy systems. The Mayo Quadratic equation can produce different values in certain creatinine ranges because of its mathematical form.

Differences between equations do not necessarily mean one lab result is wrong. They reflect different model assumptions and cohorts used during equation development. This is why trend direction over time often matters more than one isolated value.

If results fall near stage boundaries, clinicians may use repeated labs, cystatin C, or other context to improve confidence. The calculator's side-by-side display is useful for seeing this sensitivity directly.

Children require a separate approach because body composition and growth patterns differ from adults. The Schwartz equation estimates pediatric GFR using height and serum creatinine. Height is a critical term in the formula and should be entered carefully in the correct unit.

Pediatric kidney assessment should always be interpreted in a clinical context by qualified professionals. Growth stage, hydration, laboratory method, and baseline conditions can affect interpretation.

The pediatric mode in this calculator is intended to mirror common educational workflows: input creatinine and height, then review estimated filtration as a reference point for discussion with a clinician.

Serum creatinine can be reported in mg/dL or umol/L depending on region and laboratory convention. This calculator supports both and normalizes internally to mg/dL for equation consistency. Correct unit selection is essential because a unit mismatch can shift eGFR estimates significantly.

As a quick check, creatinine in umol/L is typically a larger numeric value than mg/dL. If an entered value seems unexpectedly high or low for your context, verify units before interpreting results.

Accurate input quality is one of the highest-impact factors in calculator reliability.

eGFR is commonly grouped into CKD stage categories (G1 through G5), but stage context requires more than eGFR alone. For example, G1 or G2 values may still require follow-up if there is persistent kidney-damage evidence such as albuminuria. Conversely, an isolated reduced estimate during acute illness may not represent chronic disease.

Clinical interpretation generally uses repeated measurements over time. A stable trend can imply different risk than a fast decline. Albuminuria category, blood pressure control, diabetes status, and medication exposure all influence risk stratification.

Use calculator staging as educational context only and avoid self-diagnosis from a single number.

Step 1: choose adult or pediatric mode correctly. Step 2: verify creatinine unit before entry. Step 3: enter profile fields carefully. Step 4: compare equation outputs and look for consistency. Step 5: use stage context as a guide, then discuss results with your clinician, especially when values are near thresholds or changing over time.

For follow-up tracking, record date, creatinine, and equation output. Trend visualization over months often provides more useful signal than one snapshot.

If symptoms or high-risk conditions are present, do not delay professional care regardless of calculator output.