By default, Streakster starts a week on Sunday. This can be changed in the settings.
From the home screen, press the “Gear” icon on the bottom navigation bar. Then tap on “Week Starts On” and select which day you want to start your week on.
Please note that once you’ve selected which day of the week you want your week to start on, this will affect your weekly goals, as any weekly goal will now reset on the user-defined day.