rounddate

Rounddate is a concept in date handling describing the process of converting a specific calendar date to a standardized representative date by applying a rule that maps the date to a coarser time unit. The purpose is to align dates for comparison, grouping, or reporting, so that values within the same period share a common date marker.

Rounding methods fall into several categories: floor, which rounds down to the start of the chosen unit; ceiling (or ceil), which rounds up to the start of the next unit; and round, which rounds to the nearest unit. Units commonly used include day, week, month, quarter, and year, with the option for custom intervals such as every 7 or 15 days depending on the tool.

In software and data workflows, rounddate-like functionality is provided by various date utilities. Libraries often offer floor_date, ceiling_date, or round_date types of functions, while SQL dialects may provide equivalents such as date_trunc or date_round. The exact behavior can depend on locale settings and the definitions of week or month boundaries.

Applications of rounddate include preparing time series for aggregation, generating consistent reporting periods (for example, month-ends or quarter-starts), and establishing calendar-based billing cycles or forecasting analyses. When implementing rounddate, attention to time zones and fiscal calendars is important to avoid ambiguities.

See also: date truncation, time series resampling, date arithmetic, rounding.