Julianday Converter is an app that to convert Gregorian date to Julianday. This app is the implementation of Julian Date Lib from Smart Calc library that was made by Computational Physics Laboratory, Department of Physics, Faculty of Mathematics and Sciences, Brawijaya University Malang. However this app just the first step of idea implementation, and still need more the validation how far this app usable and more accurate. Please give us a feedback about this app to: [email protected]