Week Numbers for the Year 2021

Knowing the week numbers for 2021 can be helpful for planning events, managing projects, or simply staying organized. Here’s a complete breakdown of all the weeks in 2021, including their start and end dates.

What Are Week Numbers?

Week numbers are a standardized way of counting the weeks in a year. Each week is assigned a number from 1 to 52 (sometimes 53), depending on how the calendar aligns with the start of the year. According to the ISO 8601 standard, each week starts on a Monday, and Week 1 is the week that contains the first Thursday of the year.

Week Number Table for 2021

Yes, 2021 has 53 weeks! This happens when the year starts on a Thursday or is a leap year that ends on a Thursday—allowing for that extra ISO week.

Why Are Week Numbers Useful?

Week numbers are used in a variety of scenarios across professional and personal settings:

• Software Development: Sprint planning and agile iterations often use weekly cycles.
• Business Operations: Sales goals, reporting cycles, and payroll often reference week numbers.
• Education: Academic calendars may follow weekly structures, particularly in Europe.
• Travel & Hospitality: Hotels, airlines, and tour companies often plan based on week-based pricing and schedules.

Fun Fact

The ISO 8601 week-numbering system was first introduced in 1988 and is used by many countries around the world, especially in Europe. The U.S. doesn't commonly use it, but many global systems rely on it for consistency.

Find the Week Number of Any Date

Want to know the week number of a specific date? In PHP, you can use the DateTime object like this:

Week number is: 29

List the week numbers of the coming years.

• 2025
• 2026
• 2027
• 2028
• 2029
• 2030
• 2031
• 2032
• 2033
• 2034
• 2035
• 2036
• 2037
• 2038
• 2039
• 2040
• 2041
• 2042
• 2043
• 2044
• 2045
• 2046
• 2047
• 2048
• 2049
• 2050
• 2051
• 2052
• 2053