HMMM
Handy Medical Math Machine
Calculator

Electrolyte Correction

Sodium deficit / free water deficit and potassium replacement estimates. Always correct slowly and re-check labs.

Na deficit (mEq) = TBW × (desired Na − measured Na) · FWD (L) = TBW × (Na/140 − 1)
kg
Section

Sodium correction

mmol/L
mmol/L
Correct chronic hyponatremia by a maximum of 8–10 mEq/L per 24 hours to prevent Osmotic Demyelination Syndrome (ODS). Consider entering a Desired Na of [Measured Na + 8] as a safe guide for the first 24 hours.
Sodium deficit
mEq
Total body water
L
Min. correction time (at 8 mEq/L/24h)
h
Enter weight and sodium values.
Section

Potassium replacement

mmol/L
Correction > 10 mEq/hour (via central line) MUST be accompanied by continuous ECG monitoring.
Estimated K deficit
mEq
Infusion time (peripheral · 10 mEq/h)
h
Infusion time (central · 20 mEq/h)
h
Enter weight and potassium values.