What is Tim Urban's life calendar?

Tim Urban's "life calendar" is a visual representation that he created to highlight the finite nature of human life. He uses a diagram made up of small boxes, each representing one week of a person's life, assuming they live to be 90 years old. The total number of boxes is around 4,680, and seeing how many weeks have already passed and how few are left can be a powerful motivator to make the most of one's time.

For a detailed explanation and visualization of this concept, you might want to check out Tim Urban's work directly on his blog "Wait But Why", where he dives into the concept thoroughly.