weekstart

Weekstart, also written as week start, refers to the day that marks the beginning of the calendar week in a particular system or locale. It is a configuration used for displaying dates, computing week-based intervals, and grouping data by weeks.

The choice of weekstart varies by cultural, regional, and organizational conventions. The most common options are Monday and Sunday. In many international and technical contexts, Monday is used as the start of the week, aligning with the ISO 8601 standard. In many North American contexts, Sunday serves as the first day of the week. Some systems allow other days to be set as the weekstart, depending on local practice or specific application needs.

Standards and conventions influence how weeks are numbered and displayed. Under ISO 8601, weeks begin on Monday, and week numbers are defined so that Week 01 is the first week with a Thursday of the year. This creates consistency across countries adhering to ISO conventions but may differ from local calendar practices that start on Sunday or another day.

In software and data analysis, weekstart is typically a configurable parameter. Date libraries and tools offer options to set the first day of the week for operations such as weekly resampling, reporting, and aggregations. For example, some programming libraries provide weekly frequencies anchored to a chosen weekday, and database systems may offer modes or settings that determine the week’s starting day for week-based functions.

The concept affects calendar displays, fiscal calendars, and time-based reporting, making it a key consideration in localization and internationalization of date-handling features. See also: ISO 8601, week numbering, calendar systems, localization.