wYear

wYear is a term used in some date and time systems to denote the year associated with a particular week in a week-numbering scheme, most commonly the ISO week date. In these systems, a date is described by a year, a week number, and a weekday, and the week-year (wYear) can differ from the calendar year for dates near the year’s boundaries.

The key distinction is that the wYear depends on which week the date falls into. ISO 8601 defines Week 1 as the week that contains the first Thursday of the year (equivalently, the week with Thursday). The wYear is the year that corresponds to that week. As a result, some early January dates can belong to the previous calendar year’s week-year, while late December dates can belong to the next year’s week-year. For example, 2021-01-02 typically has wYear 2020, whereas 2021-01-04 has wYear 2021.

In programming and data processing, wYear is often referred to as the week-based year or week-year. Libraries may expose it as a distinct field or through patterns such as WeekBasedYear or WeekYear. In Java and related ecosystems, the difference between calendar year and week-year is encountered when formatting or parsing dates, using mechanisms like WeekFields.ISO or patterns that distinguish year types.

The wYear facilitates consistent weekly labeling across year boundaries and is defined by standards such as ISO 8601. It is used in calendars, scheduling, and data analyses where week-based reporting is required.