Skip to main content

WeekOfTheMonth

Function WeekOfTheMonth( const AValue : TDateTime) : Word

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := WeekOfTheMonth(EncodeDate(2024, 6, 1));
  // Value is 5: this Saturday belongs to the final ISO week of May.
end;

Usage​

WeekOfTheMonth returns the ISO 8601x week-of-month number assigned to an encoded date/time value.

Parameters

NameTypeDescription
AValueTDateTimeA valid encoded date/time. Only its Gregorian date is used.

Returns

The numbered week within the month that owns the ISO week. In Velox the calculation produces 1 through 5.

Behaviour

This is a week-ownership calculation, not the ordinal occurrence of the date's weekday. For example, the first Saturday of a month can still be week 4 or 5 of the preceding month. Use NthDayOfWeek when the requirement is "the first Saturday" rather than an ISO week number.

Errors

Velox does not catch exceptions. Any conversion or range exception from the installed RTL propagates.

Additional Technical Info​

Returns the one-based ISO-style week-of-month number assigned to AValue. Weeks run from Monday through Sunday. The first week owned by a month is the first week containing at least four days in that month, so a boundary date can belong to a neighbouring month's numbered week.

Implementation

Velox binds directly to the one-argument System.DateUtils.WeekOfTheMonth overload. It calls DecodeDateMonthWeek, discarding the decoded owner year, owner month and ISO weekday. The decoder obtains the weekday of the month's first day, offsets the day number so Monday-based four-day weeks align, and rounds a positive adjusted day number up to a week. It recursively decodes the prior month's last day when the adjusted number is zero or negative, and assigns qualifying Monday-to-Wednesday month-end dates to week 1 of the next month.

Edge cases and quirks

  • Velox exposes only the week number. At a boundary, the result alone does not identify whether it belongs to the previous, current or next month; DecodeDateMonthWeek returns that owner information.
  • The current DocWiki page says the result can be 1 through 6. The installed source's offset and month-length bounds produce 1 through 5; Velox follows the installed source.
  • Time-of-day, locale and host timezone do not affect the result.
  • The input must be within the supported encoded Gregorian range. An invalid lower-bound value leads to an RTL conversion error during month-start encoding.

Performance and concurrency

The calculation uses bounded date decoding and, at most, one adjacent-month recursive step. It allocates no objects and uses no Velox shared state.

Related entries

  • DecodeDateMonthWeek — returns the owner year, owner month, week number and ISO weekday.
  • WeekOfTheYear — applies the corresponding four-day rule to ISO week-years.
  • NthDayOfWeek — returns the ordinal occurrence of a weekday in the literal calendar month.

External references

Created 2026-07-15