A free water and sodium calculator app is available for download for iOS, Android. The app was created by Daniel Batlle from Northwestern University. The app focuses on commonly used formulas for water and sodium. While there are many apps available with sodium and water formulas, this one goes the extra mile to give some much needed extras. Click on the information icon on the upper right of the app and you get explanations of the formulas, a discussion of the concept, clinical utility, gives a clinical example, limitations/caveats, and references. Overall, this is a nice app and we highly recommend. Plus it is free.