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Wednesday, February 5, 2025
ISO 8601
Week 6
Starts on Monday
  • Year start rule: First week must include January 4th
    • US Traditional
    Week 6
    (Standard US System)
    Starts on Sunday
  • Year start rule: First week includes January 1st
    • US Broadcast Calendar
    Week 6
    Starts on Monday
  • Year start rule: Week containing January 1st is week 1
    • US Accounting
    Week 6
    Starts on Sunday
  • Year start rule: Week containing January 1st is week 1

    • Week Numbers Explained

    Current Time Across Time Zones

    US Pacific

    Wednesday, February 5, 2025 at 11:21 AM Pacific Standard Time

    ISO Week: 6US Week: 6

    US Eastern

    Wednesday, February 5, 2025 at 2:21 PM Eastern Standard Time

    ISO Week: 6US Week: 6

    UK

    Wednesday, February 5, 2025 at 7:21 PM Greenwich Mean Time

    ISO Week: 6US Week: 6

    Central Europe

    Wednesday, February 5, 2025 at 8:21 PM Central European Standard Time

    ISO Week: 6US Week: 6

    India

    Thursday, February 6, 2025 at 12:51 AM India Standard Time

    ISO Week: 6US Week: 6

    Japan

    Thursday, February 6, 2025 at 4:21 AM Japan Standard Time

    ISO Week: 6US Week: 6

    Australia Eastern

    Thursday, February 6, 2025 at 6:21 AM Australian Eastern Daylight Time

    ISO Week: 6US Week: 6

    New Zealand

    Thursday, February 6, 2025 at 8:21 AM New Zealand Daylight Time

    ISO Week: 6US Week: 6

    Note: Week numbers are based on the calendar date in each timezone. While most days will show the same week numbers worldwide, differences can occur near date boundaries when some locations are already on the next day.

    When Do Week Numbers Differ?

    Week numbers can differ between locations in these cases:

    • At year boundaries (Dec 31/Jan 1) when timezones are on different years
    • At week boundaries when timezones are on different dates
    • During week 1 calculation in January (different systems, different dates)

    Example: When it's Sunday 11:59 PM in New York, it's already Monday in London. If this is at a week boundary, London will show the next week's number.

    ISO Week Numbers (European Standard)

    The ISO week numbering system (ISO-8601) defines weeks as follows:

    • Weeks start on Monday
    • Week 1 is the week containing the first Thursday of the year (this ensures the week belongs to the year that contains most of its days)
    • Each week belongs to exactly one year, but December 31 might be in week 1 of next year, or January 1 might be in week 52/53 of previous year
    • Most commonly used in Europe and international standards

    Examples of year transitions:

    • 2024/2025: The last days of December 2024 will be in week 1 of 2025 because January 2nd, 2025 is a Thursday
    • 2025/2026: The last days of December 2025 will be in week 1 of 2026 because January 1st, 2026 is a Thursday

    US Week Numbers

    The US week numbering system (reference) follows these rules:

    • Weeks start on Sunday (following the traditional US calendar)
    • Week 1 is the first week containing January 1st
    • Weeks always belong to the current calendar year (1-54)
    • Commonly used in the United States and some business applications

    Note: This system can result in partial weeks at the beginning and end of the year.

    Why Different Systems?

    Multiple week numbering systems exist worldwide due to cultural, religious, and business practices (reference):

    • ISO 8601 provides international standardization for business and commerce
    • US Traditional system aligns with traditional American and Western calendar practices
    • US Broadcast Calendar serves specific industry needs for TV/radio programming
    • US Accounting serves specific industry needs for financial accounting

    While ISO 8601 aims to standardize week numbering globally, regional and industry-specific systems continue to serve important cultural and practical purposes in their respective contexts.

    Global Week Numbering Systems

    Different regions use various week numbering systems based on cultural and business needs:

    ISO 8601

    • First day: Monday
    • Year start rule: First week must include January 4th
    • Used in: International standard, widely used in Europe and business
    • Weeks are assigned to the year containing most of their days. A year has 52 or 53 full weeks.

    US Traditional

    • First day: Sunday
    • Year start rule: First week includes January 1st
    • Used in: United States, parts of North America
    • Has partial weeks at year start/end. 52 full weeks plus 1-2 partial weeks possible.

    US Broadcast Calendar

    • First day: Monday
    • Year start rule: Week containing January 1st is week 1
    • Used in: US Broadcasting Industry
    • Similar to ISO but defines week 1 differently. Up to 6 days of December may be in week 1.

    US Accounting

    • First day: Sunday
    • Year start rule: Week containing January 1st is week 1
    • Used in: US Financial Sector
    • A hybrid system with 52 or 53 weeks per year

    Source: Wikipedia: Week Numbering Systems