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WeeksInYear

Function WeeksInYear( const AValue : TDateTime) : Word

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := WeeksInYear(EncodeDate(2020, 12, 31));
  // Value is 53 because the encoded calendar year is 2020.
end;

Usage​

WeeksInYear returns the 52- or 53-week ISO count for the calendar year encoded in a date/time value.

Parameters

NameTypeDescription
AValueTDateTimeA valid encoded date/time whose Gregorian year supplies the input to WeeksInAYear.

Behaviour

The time component is ignored. Locale and timezone settings are not consulted. The function answers a property of the encoded Gregorian year, not a property of the date's ISO week owner.

Errors

Velox does not catch RTL exceptions. Invalid encoded dates or invalid derived years can produce a date conversion error.

Additional Technical Info​

Returns the number of ISO 8601 weeks in the Gregorian calendar year component of AValue. The result is 52 or 53.

Implementation

Velox binds directly to System.DateUtils.WeeksInYear. The installed function calls YearOf(AValue), then passes that calendar year unchanged to WeeksInAYear. The latter encodes 1 January and applies the ISO Thursday/leap-year rule.

Edge cases and quirks

  • Around New Year, YearOf(AValue) can differ from the ISO week-year returned by DecodeDateWeek. WeeksInYear deliberately uses the calendar year. For example, a late-December date in ISO week 1 of the following year still returns the week count for its December calendar year.
  • A date's returned WeekOfTheYear should therefore not automatically be paired with WeeksInYear when constructing an ISO year/week key.
  • For an invalid lower-bound encoded date, YearOf returns 0 and WeeksInAYear(0) then raises while encoding 1 January.

Performance and concurrency

The routine performs bounded date decoding and encoding without object allocation or Velox shared state.

Related entries

  • WeeksInAYear — accepts the year explicitly.
  • YearOf — supplies the calendar year used here.
  • DecodeDateWeek — returns the ISO week-year required for an ISO year/week key.

External references

Created 2026-07-15