Calendar weeks are a system of dividing the year into 52 or 53 periods of seven days each, with each week beginning on Monday and ending on Sunday. The first calendar week of a year is the week that contains January 1st. Calendar weeks are used for scheduling and planning purposes in many countries around the world.
In 2025, the first calendar week will begin on Monday, January 1st and end on Sunday, January 5th. The last calendar week of 2025 will begin on Monday, December 29th and end on Sunday, January 4th, 2026. Calendar weeks can be a helpful way to track the passage of time and plan for upcoming events.