Calendars and time
ISO Week Date
Direct answer
ISO Week Date: An ISO Week Date identifies a date by week-numbering year, week number, and weekday, with weeks beginning on Monday.
An ISO Week Date writes dates as a week-year, numbered week, and weekday.
$0 today, then $12/month after 7 days. Cancel anytime.
At a glance
- Found in
- Calendars & Timekeeping
- Related
- Revised Julian Calendar, Ordinal Date, Calendar, Julian Date
An ISO Week Date writes dates as a week-year, numbered week, and weekday.
A cycle or timeline schematic for comparing the named timekeeping concept.
What does your own chart say about you?
Choose love, work or purpose. Your reading is written from your chart. Your reading uses your own birth details.
Walk through Alex’s whole example first
The Road of AgesSee the turning points of your whole life, from your birth date
See your road's shape
Prefer to explore first?
The Road of AgesThe turning points of your whole life, from your own chart
Walk my road
Free, by email
Your daily Almanac letter
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
The story behind ISO Week Date
International standardization formalized a Monday-based week in which week 01 contains the year first Thursday.
Why ISO Week Date matters
ISO Week Date supports unambiguous weekly reporting across month and year boundaries, especially in logistics and data systems.
How to read ISO Week Date
ISO Week Date speaks to week-based schedules and datasets that follow the ISO rule for week 01.
ISO Week Date in practice: an example
January 1 can belong to the final ISO week of the preceding week-numbering year.
Where readings of ISO Week Date go wrong
It is a mistake to assume the ISO week-year always equals the Gregorian calendar year printed beside the same day.
Sources and editorial method
Research references used for this entry include:
- ISO: ISO 8601 Date and Time Format - Standards-body overview of unambiguous international date and time representations.
- IAU SOFA: Time Scale and Calendar Tools - IAU-standard algorithms and guidance for civil calendars, Julian dates, and seven recognized astronomical time scales.
- Source
- The Great Almanac Dictionary
- Category
- Calendars & Timekeeping
- Last updated
- 2026-09-26
Verify the week-numbering year
A definition tells you what it is; your own birth chart tells you what it means for you. The Oracle casts your real chart and answers for your love, your work, and your year ahead, in conversation. It opens with the 7-day Seeker trial.
Speak with the OracleRelated terms
More in Calendars & Timekeeping
- Local Sidereal Time
- Proleptic Gregorian Calendar
- Solar Calendar
- UT1
- Barycentric Coordinate Time
- Civil Day
- DUT1
- GPS Time
From the reference page to your own chart
Every word here
is in your own chart.
- A personal reading about love, work or purpose, written from your chart
- A practical next step to consider
- It opens with 7 days free, with the AI Oracle and daily guidance
$0 today, then $12/month after 7 days. Cancel anytime.
Common questions
What is an ISO Week Date?
An ISO Week Date identifies a date by week-numbering year, week number, and weekday, with weeks beginning on Monday.
What do people get wrong about an ISO Week Date?
It is a mistake to assume the ISO week-year always equals the Gregorian calendar year printed beside the same day.
Free, by email
The Almanac, in your inbox at 7
One short letter at 7 each morning: the day’s theme read for your own chart, and one thing to do with it.
