WhatsApp is one of the most widely used instant messaging apps on mobile devices, thanks to its low data usage and ability to be used internationally. Unfortunately, the instant messaging application does not allow users to control their online or offline status. (Each time a user opens the application, they are shown as "online" to all of their contacts.)
Luckily, for users who would like to use the application in "Offline Mode," there are several possible workaround solutions.
Hide Online Status on WhatsApp
Appear Offline on WhatsApp for Android
Android users who want to appear offline can do so by simply disabling their internet connection.
Alternatively, the W-Tools application (available on Google Play) can be used to achieve an offline status on WhatsApp.
Appear Offline on WhatsApp for iPhone
iPhone users can achieve offline status through a quick tweak to their user settings.
Launch WhatsApp and head to your Settings tab, located in the bottom right hand corner.
Next, go to Chat Settings/Privacy > Advanced. Toggle the Last Seen Timestamp option to OFF, and then select Nobody to disable the application timestamps. This method will allow you to continue in "offline" mode.
Note that this process can be reversed by simply toggling the Last Seen Timestamp option to ON.