A streak is calculated when you complete all three daily tasks for two or more consecutive days.
Here's how it works:
Maintaining A Streak
Complete all three tasks in your "Daily Tasks" section each day. If you miss one task by 12am the next day, your streak is considered broken.
Reviving A Streak
If you miss a day, you can revive your streak by going back (up to one day) and completing the unfinished tasks.