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14 Nephrology Calculators – Kidney Function, Electrolytes & Urine

Nephrology calculators cover kidney-function and dialysis estimates, serum electrolyte and water arithmetic, acid-base measures, urine ratios, output, and fractional excretion. Their inputs and intended uses differ even when the same analyte appears.

Distinguish indexed eGFR from Cockcroft–Gault creatinine clearance, and keep paired serum and urine measurements or dialysis samples within the timing requirements stated on the selected page.

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Choose a calculator by task

Use the task groups below to find the calculator whose formula, intended population, required measurements, and purpose match the task.

Kidney-function and dialysis estimates

Choose between adult CKD-EPI eGFR, historical Cockcroft–Gault creatinine clearance, and protocol-dependent hemodialysis adequacy arithmetic.

Adult eGFR CalculatorEstimate adult race-free indexed glomerular filtration rate (eGFR) with 2021 CKD-EPI creatinine, 2012 cystatin C, or 2021 combined equations.CrClCockcroft–Gault Creatinine Clearance CalculatorEstimate adult Cockcroft–Gault creatinine clearance in mL/min from an explicit weight basis, without automatic weight selection or a dosing recommendation.spKt/V & URRAdult Single-Pool Kt/V (Daugirdas II) & URR CalculatorCalculate adult Daugirdas II single-pool Kt/V and URR for one completed intermittent hemodialysis treatment using paired sampling and actual delivered time; no adequacy classification or prescription.

Serum electrolytes, osmolality, and water

Use measured serum inputs and the specified units for hyperglycemia-adjusted sodium, calculated osmolality, or free-water-deficit arithmetic.

Adjusted Na⁺Hyperglycemia-Adjusted Sodium Calculator (Katz & Hillier)Compare Katz 1.6 and Hillier overall 2.4 hyperglycemia-adjusted sodium estimates from measured sodium and paired glucose in mg/dL or mmol/L, without selecting a primary model.Calculated Serum Osmolality, Tonicity & Osmolal Gap CalculatorCalculate serum osmolality and effective osmolality (tonicity), with optional measured osmolality, osmolal gap, and separate ethanol assumptions; no toxic-alcohol or HHS diagnosis.Free Water Deficit Calculator (Explicit TBW Coefficient)Estimate a static positive free water deficit for hypernatremia when current sodium is >145 mmol/L or mEq/L, using an explicitly selected lower target, kg or lb weight, and an explicit TBW coefficient, with estimated TBW and results in L and mL—not an infusion volume or treatment output.

Acid-base arithmetic

Select the albumin-adjusted serum anion gap, urine anion gap, or bicarbonate-deficit estimate according to the required measurements and assumptions.

Adjusted AGAlbumin-Adjusted Anion Gap Calculator (Figge 2.5)Calculate a signed sodium-only Figge 2.5 albumin-adjusted anion gap from same-specimen or paired chemistry and albumin in g/dL or g/L, with no universal interval, diagnosis, delta ratio, or treatment output.Urine Anion Gap Calculator (Na + K − Cl)Calculate the one-decimal signed urine anion gap from sodium, potassium, and chloride in the same urine specimen using mmol/L or mEq/L, without treating UAG as direct urine ammonium or a universal positive/negative diagnosis.Estimated Bicarbonate Deficit Calculator (Explicit Distribution Factor)Estimate a static positive bicarbonate deficit in mEq from submitted bicarbonate, an externally selected higher target, kg or lb weight, and an explicit distribution factor; not blood-gas base deficit, a sodium bicarbonate dose, product volume, or treatment output.

Urine and renal-handling measures

Match urine protein, urine output, BUN/creatinine, FENa, or FEUrea inputs to the stated collection and paired-sample requirements.

Spot Urine Protein-to-Creatinine Ratio Calculator (UPCR / PCR)Calculate a same-specimen spot urine total protein-to-creatinine ratio in mg/mg, mg/g, and mg/mmol; not ACR, 24-hour protein, or a diagnosis.Measured Urine Output Rate Calculator (mL/hr & mL/kg/hr)Calculate measured urine output for one completed collection interval as average mL/hr and average mL/kg/hr using protocol-selected weight, without AKI diagnosis, stage, or treatment output.BUN/Cr RatioBUN-to-Creatinine Ratio CalculatorCalculate a same-specimen or clinically paired conventional BUN-to-creatinine ratio after exact normalization of BUN mg/dL or urea mmol/L and creatinine mg/dL or µmol/L, without diagnostic or treatment output.Fractional Excretion of Sodium (FENa) CalculatorCalculate fractional excretion of sodium from paired urine and serum sodium plus independently normalized urine and serum creatinine in mg/dL or µmol/L, returning a percentage without a universal cutoff, AKI-cause classification, or treatment output.Fractional Excretion of Urea (FEUrea) CalculatorCalculate paired urine and serum FEUrea (FEUN) after independent exact normalization of BUN mg/dL or whole urea mmol/L and urine/serum creatinine in mg/dL or µmol/L, with no AKI-cause or treatment output.

How to choose a calculator in this category

  • Use eGFR for its indexed CKD-EPI estimate and Cockcroft–Gault only when that historical creatinine-clearance model is the required metric; they are not interchangeable.
  • For FENa, FEUrea, and urine calculations, verify paired measurements, collection duration, units, and timing before calculation.
  • For Kt/V, follow the stated hemodialysis blood-sampling and treatment-session protocol rather than mixing values from unrelated time points.

Important limits

  • A calculated kidney-function or urine result does not by itself diagnose acute kidney injury or chronic kidney disease.
  • Changing biomarkers, non-steady-state creatinine, collection error, and nonrenal determinants can limit these estimates.
  • These pages do not generate medication doses, dialysis prescriptions, referral instructions, or treatment decisions.

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