yearweek

Yearweek is a combined representation of a calendar year and a week number used to label weekly intervals in time-series data, reporting, and scheduling. It allows analysts to group or compare data on a weekly basis without relying on specific calendar dates.

The most widely used convention is the ISO-8601 week date system. In ISO weeks, weeks start on Monday, and Week 1 is the week that contains the year's first Thursday (equivalently the week with January 4). A yearweek value is often written in a format such as 2024-W23 or, in some databases, as 202423 (year followed by the two-digit week). Different systems may use different formats, so it is important to know the convention in use when integrating data from multiple sources.

In practice, yearweek values can be derived from dates using various functions. For example, many SQL dialects offer a YearWeek or YEARWEEK function that returns a numeric year-week representation. Programming languages provide equivalents based on isocalendar or ISO week calculations. The key point is that yearweek encodes the week label rather than a precise day, which can simplify weekly aggregations but requires consistent handling across tools.

Yearweek systems must address cross-year boundaries. Some years have 53 ISO weeks, causing the final weeks of a year to belong to the next year’s sequence, and the first weeks of the new year may belong to the previous year’s ISO week count. This can affect reporting continuity and alignment with fiscal calendars.

Uses for yearweek include weekly sales analysis, weather patterns, project timelines, and any scenario needing stable weekly grouping.