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WeeksInAYear

Function WeeksInAYear( const AYear : Word) : Word

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := WeeksInAYear(2020);
  // Value is 53.
end;

Usage​

WeeksInAYear returns whether a supplied ISO week-year contains 52 or 53 weeks.

Parameters

NameTypeDescription
AYearWordGregorian year from 1 through 9999 whose ISO week count is required.

Behaviour

A 53-week year is one whose calendar layout leaves 53 Thursdays in the ISO week-year: a common year beginning on Thursday, or a leap year beginning on Wednesday or Thursday. Locale first-day-of-week settings do not alter the calculation.

Errors

An invalid year causes the installed EncodeDate Velox to raise a date conversion error. Velox does not catch it.

Additional Technical Info​

Returns the number of ISO 8601 weeks in AYear. A valid year has either 52 or 53 ISO weeks.

Implementation

Velox binds directly to System.DateUtils.WeeksInAYear. The installed routine starts with 52, encodes 1 January of AYear, obtains its ISO weekday and adds one week when 1 January is Thursday, or when it is Wednesday in a leap year. This is the standard consequence of assigning the first ISO week to the week containing the year's first Thursday.

Edge cases and quirks

  • AYear is a Word, so the scripting declaration accepts numeric values beyond the supported Gregorian year. The implementation does not pre-check the range; its EncodeDate(AYear, 1, 1) call raises for 0 or a value above 9999.
  • The result describes an ISO week-year, not the count of arbitrary seven-day periods in 365 or 366 days.
  • Free Pascal documents the equivalent 52/53 rule. Installed Delphi 37.0 source remains authoritative for the exposed Velox routine.

Performance and concurrency

The routine performs one date encoding plus fixed arithmetic and allocates no objects.

Related entries

  • WeeksInYear — obtains the calendar year from a TDateTime before applying this function.
  • WeekOfTheYear — returns the ISO week containing a date.
  • IsInLeapYear — tests whether an encoded date falls in a leap year.

External references

Created 2026-07-15