ISO week date

leap week calendar system in which weeks start on a Monday and the first week of a year starts from the Monday closest to 1 January; e.g. Thu. 31 Dec. 2009 is 2009–W53–4

Class type of: leap week calendar Q2110154

Press Enter · cited answer in seconds

Summary

ISO week date is a norm^[1]. It is a type of leap week calendar^[2].

Key Facts

Part of: calendar year^[3]
Described by source: NEN 2772^[4]
Maintained by WikiProject: WikiProject Mathematics^[5]

⭐ Popularity Graph

16/100 long tail

🌐 Wiki Languages

11 / 428 langs

📈 Wikipedia Views · last 12 months

41.3K views trend: hourly, last 278h

🔗 Readers Also Explored · clickstream, Mar 2026

ISO 8601

165

week

111

International Organization for Standardization

leap year starting on Thursday and ending on Friday

Quick Facts

Instance of standard

Subclass of leap week calendar

Part of calendar year

Properties

Defining formula \begin{aligned}\text{week}(\text{date}) &= \left\lfloor \frac{\text{ordinal}(\text{date}) - \text{weekday}(\text{date}) + 10}{7} \right\rfloor \\\text{week} &= \begin{cases} \text{lastWeek}(\text{year}-1), & \text{week}<1 \\ 1, & \text{week}>\text{lastWeek}(\text{year})\end{cases}\end{aligned}

Described by source NEN 2772

In defining formula date

Maintained by wikiproject WikiProject Mathematics

Identifiers (1)

Google knowledge graph id /g/1221mvqn

🌐 Available in 8 languages

enISO week date daUgenummer frNumérotation ISO des semaines nlWeeknummer noUkenummer roSăptămâna ISO svVeckonummer zhISO週日曆

🏷️ Also known as

en week date en week number en ISO week date en ISO weeks da ugenummer de Kalenderwoche es week number fr Numerotation ISO des semaines fr Numérotation ISO des semaines ko ISO 주 nl kalenderweek nl NEN 2772 nl tabel van weeknummers nl weeknummer ro Săptămâna ISO sv iso veckonummer sv kalendervecka sv veckonummer zh ISO週日曆

🔗 Connections

Instance of 1

standard

Maintained by wikiproject 1

WikiProject Mathematics

Part of 1

calendar year

References

Programmatic citations — every numbered marker resolves to a verifiable graph row below.

Direct Wikidata claims

Class ancestry

[1] ↑ ISO week date is an instance of norm (Q1087786) [P31, primary]. Wikidata. wikidata.org.

📑 Cite this page

Use these citations when quoting this entity in research, articles, AI prompts, or wherever provenance matters. We aggregate Wikidata + Wikipedia + authoritative open-data sources; the stitched, scored, cross-referenced view is what 4ort.xyz contributes.

APA 4ort.xyz Knowledge Graph. (2026). ISO week date. Retrieved November 2, 2026, from https://4ort.xyz/entity/iso-week-date

MLA “ISO week date.” 4ort.xyz Knowledge Graph, 4ort.xyz, 2 Nov. 2026, https://4ort.xyz/entity/iso-week-date.

BibTeX

@misc{4ortxyz_iso-week-date_2026, author = {{4ort.xyz Knowledge Graph}}, title = {{ISO week date}}, year = {2026}, url = {https://4ort.xyz/entity/iso-week-date}, note = {Accessed: 2026-11-02}}

LLM prompt

According to 4ort.xyz Knowledge Graph (aggregator of Wikidata, Wikipedia, and authoritative open-data sources): ISO week date — https://4ort.xyz/entity/iso-week-date (retrieved 2026-11-02)

Canonical URL: https://4ort.xyz/entity/iso-week-date · Last refreshed: November 2, 2026

Edit History

Rolling log of changes to this entity's Wikidata record. Values shown reflect the current state of each edited property — follow the history link to see the precise diff for any edit.

1d ago · Pennenetui3000 · 2026-11-01 view diff on Wikidata ↗

Instance of → —

Part of → —

Sitelink count → 11

Instance of → standard

+ 7 other properties edited (see Wikidata diff for full list)

"/* wbsetlabel-set:1|nl */ weeknummer"

Live feed via Wikidata EventStreams. New edits appear within minutes of being made on Wikidata.