Rapid correction of the dysnatremias can result in significant patient morbidity and mortality. To avoid overly rapid correction of the dysnatremias, the sodium deficit equation, water deficit equation, and Adrogue-Madias equation are frequently utilized to predict the change in plasma sodium concentration (Delta[Na+]p) following a therapeutic maneuver. However, there are significant limitations inherent in these equations. Specifically, the sodium deficit equation assumes that total body water (TBW) remains unchanged. Similarly, when using the Adrogue-Madias equation, the volume of infusate required to induce a given Delta[Na+]p is determined by dividing the target Delta[Na+]p by the result of this formula. This calculation also assumes that TBW remains constant. In addition, neither of these equations are applicable in the management of symptomatic syndrome of inappropriate antidiuretic hormone secretion (SIADH) because they fail to consider the subsequent increase in sodium excretion following the administration of infusate. Furthermore, in the treatment of hypernatremia, the water deficit equation is only applicable if the hypernatremia is caused by pure water loss. In hypernatremia caused by hypotonic fluid losses, the water deficit equation does not provide any information on the differential effect of infusates of variable [Na+] and [K+] on the [Na+]p. Finally, all these equations fail to consider any ongoing Na+, K+, or H2O losses. Taking all these limitations into consideration, we have derived two new equations which determine the volume of a given infusate required to induce a target Delta[Na+]p. These equations consider the mass balance of Na+, K+, and H2O, as well as therapy-induced changes in TBW. The first equation is applicable to both hypernatremia and hyponatremia. The second equation is applicable to the management of severe symptomatic SIADH requiring intravenous therapy.