Sodium Deficit Calculator

About this calculator

In hyponatremia, the sodium deficit estimates how much sodium (in mEq) would need to be replaced to raise a person's serum sodium from its current, low level to a chosen target: Sodium deficit = TBW × (Target Na − Current Na), where total body water (TBW) is approximated as a fraction of body weight — roughly 0.6 in men and 0.5 in women, lower in the elderly — reflecting that sodium distributes through all of the body's water, not just the bloodstream.

This calculation, closely related to the Adrogué-Madias approach to correcting sodium disorders, is a bedside tool in hospital medicine and nephrology: it gives clinicians a starting estimate of the correction needed, which is then weighed against strict safe correction-rate limits to avoid complications like osmotic demyelination from correcting sodium too quickly.

Physicians, nurses, and medical students working through electrolyte disorders use it as a teaching and quick-reference calculation — it estimates the deficit only, not a treatment plan, since actual correction always accounts for the rate limits and clinical context an individual patient requires.