Kidney calculators
Calculators for patients, families, students and clinicians. Each one names the study or guideline it comes from. Nothing you type leaves your device.
For patients and families
Use these before your appointment and bring the results so we can talk about them together. They are estimates for learning, not a diagnosis.
How much water should I drink?
A daily estimate from your weight and age. If you know your blood sodium from a recent lab, add it: a low or high sodium changes the advice, and it always deserves a look for the cause. This assumes you do not take a water pill (diuretic).
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academies Press; 2005.
- Holliday MA, Segar WE. The maintenance need for water in parenteral fluid therapy. Pediatrics. 1957;19:823-832.
- Adrogué HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342:1493-1499.
- Verbalis JG, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1-S42.
- Pearle MS, et al. Medical management of kidney stones: AUA guideline. J Urol. 2014;192:316-324.
Fluid converter and daily limit planner
Convert cups, ounces, milliliters and liters. If you have a fluid limit, enter it to see it in every unit and spread across your day.
Kidney failure risk (KFRE)
The Kidney Failure Risk Equation estimates the chance of needing dialysis or a transplant within 2 and 5 years. It is meant for people with an eGFR between 10 and 59. Your eGFR is on your lab report.
- Tangri N, et al. A predictive model for progression of chronic kidney disease to kidney failure. JAMA. 2011;305:1553-1559.
- Tangri N, et al. Multinational assessment of accuracy of equations for predicting risk of kidney failure: a meta-analysis. JAMA. 2016;315:164-174.
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314.
Home blood pressure average
Measure seated after 5 minutes of rest, arm supported at heart level. Take 2 readings in the morning and 2 in the evening for 3 to 7 days.
If any reading is 180/120 or higher with chest pain, shortness of breath, weakness or vision changes, call 911.
For clinicians and students
Decision support for clinicians and trainees in the hospital, the dialysis unit and the classroom. These estimates do not replace clinical judgment: confirm inputs, recheck labs, and follow your institution’s protocols.
Sodium and water
Sodium corrected for glucose
Hyperglycemia draws water out of cells and dilutes sodium. Both common correction factors are shown.
Free water deficit (hypernatremia)
Estimated water needed to bring sodium to the target, and a safe pace to give it.
Infusate effect on sodium (Adrogué–Madias)
Predicted change in serum sodium from 1 liter of a fluid, the volume to reach your 24-hour goal, and the rate.
- Adrogué HJ, Madias NE. Hyponatremia. N Engl J Med. 2000;342:1581-1589.
- Verbalis JG, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1-S42.
- Spasovski G, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol. 2014;170:G1-G47.
Serum osmolality and osmolal gap
Calculated osmolality, and the gap to the measured value (toxic alcohols, mannitol, others).
Urine electrolytes: free water clearance and fluid restriction
The urine-to-serum electrolyte ratio predicts whether fluid restriction can correct hyponatremia (SIAD), and how strict it must be.
- Furst H, et al. The urine/plasma electrolyte ratio: a predictive guide to water restriction. Am J Med Sci. 2000;319:240-244.
- Verbalis JG, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1-S42.
- Rose BD, Post TW. Clinical Physiology of Acid-Base and Electrolyte Disorders. 5th ed. McGraw-Hill; 2001.
Kidney function and AKI
eGFR and creatinine clearance for drug dosing
CKD-EPI 2021 eGFR (indexed and de-indexed to body size) and Cockcroft–Gault creatinine clearance. Only valid when creatinine is stable.
- Inker LA, et al. New creatinine- and cystatin C-based equations to estimate GFR without race. N Engl J Med. 2021;385:1737-1749.
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16:31-41.
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (drug dosing, chapter 4). Kidney Int. 2024;105(4S):S117-S314.
FENa and FEUrea
Fractional excretion of sodium and of urea to separate prerenal states from tubular injury. FEUrea is more useful after diuretics.
AKI stage (KDIGO)
Stage by creatinine and urine output. The higher of the two defines the stage.
Contrast-associated kidney injury risk
Intra-arterial (cardiac catheterization): Mehran risk score. Intravenous (CT): the 2020 ACR–NKF consensus by eGFR.
- Mehran R, et al. A simple risk score for prediction of contrast-induced nephropathy after percutaneous coronary intervention. J Am Coll Cardiol. 2004;44:1393-1399.
- Davenport MS, et al. Use of intravenous iodinated contrast media in patients with kidney disease: consensus statements from the American College of Radiology and the National Kidney Foundation. Radiology. 2020;294:660-668.
- Weisbord SD, et al. Outcomes after angiography with sodium bicarbonate and acetylcysteine (PRESERVE). N Engl J Med. 2018;378:603-614.
Acid–base and minerals
Anion gap, delta ratio and Winters’ formula
Albumin-corrected anion gap, the delta ratio for mixed disorders, and the expected pCO₂ for a metabolic acidosis.
- Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26:1807-1810.
- Rastegar A. Use of the ΔAG/ΔHCO3- ratio in the diagnosis of mixed acid-base disorders. J Am Soc Nephrol. 2007;18:2429-2431.
- Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis. Ann Intern Med. 1967;66:312-322.
Calcium corrected for albumin
A quick estimate. In kidney disease and critical illness, an ionized calcium is more reliable.
Dialysis and CRRT
CRRT sodium planner: fixing hypo- or hypernatremia on the circuit
Single-pool sodium kinetic model. Enter where you want the sodium to be in 24 hours; it returns the effective CRRT fluid sodium needed, how to make it (sterile water or 23.4% NaCl added to the bags, or a post-filter D5W or 3% NaCl infusion), and the effluent rate that would reach the goal with standard 140 mmol/L fluid.
- Yessayan L, Yee J, Frinak S, Szamosfalvi B. Treatment of severe hyponatremia in patients with kidney failure: role of continuous venovenous hemofiltration with low-sodium replacement fluid. Am J Kidney Dis. 2014;64:305-310.
- Yessayan LT, Szamosfalvi B, Rosner MH. Management of dysnatremias with continuous renal replacement therapy. Semin Dial. 2021;34:472-479.
- Watson PE, Watson ID, Batt RD. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr. 1980;33:27-39.
CRRT dose (effluent mL/kg/h)
Prescribed effluent dose, corrected for pre-filter dilution.
- KDIGO Clinical Practice Guideline for Acute Kidney Injury (recommendation 5.8.4). Kidney Int Suppl. 2012;2:1-138.
- VA/NIH Acute Renal Failure Trial Network. Intensity of renal support in critically ill patients with acute kidney injury. N Engl J Med. 2008;359:7-20.
- RENAL Replacement Therapy Study Investigators. Intensity of continuous renal-replacement therapy in critically ill patients. N Engl J Med. 2009;361:1627-1638.
Hemodialysis adequacy: Kt/V and URR
Single-pool Kt/V (Daugirdas second generation) and urea reduction ratio from pre- and post-dialysis BUN.
Lab unit converter
Convert lab units (U.S. ↔ SI)
For international labs, papers and students.
These tools are for education and decision support only and do not replace medical advice. Never change a medicine or your fluids on your own because of a result.