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WeeksBetween

Function WeeksBetween( const ANow, AThen : TDateTime) : Integer

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := WeeksBetween(EncodeDate(2026, 1, 1), EncodeDate(2026, 1, 20));
  // Value is 2. The remaining five days are discarded.
end;

Usage​

WeeksBetween returns the absolute number of complete seven-day periods between two millisecond-normalised date/time values.

Parameters

NameTypeDescription
ANowTDateTimeOne encoded date/time endpoint. The name does not require it to be later than AThen.
AThenTDateTimeThe other encoded date/time endpoint.

Returns

A non-negative Integer containing the number of complete 604,800,000-millisecond periods. Any fractional week is discarded.

Behaviour

Parameter order is interchangeable because the difference is made absolute. Timestamp conversion rounds the encoded floating-point value to millisecond resolution before subtraction. A gap one millisecond short of seven days returns 0; exactly seven days returns 1.

Errors

There is no validation or exception handling in the Velox binding. Arithmetic or conversion failures for values outside the representable TDateTime range propagate.

Additional Technical Info​

Returns the absolute number of complete seven-day periods between ANow and AThen. It measures encoded timestamp distance; it does not count crossed ISO week numbers or Monday boundaries.

Implementation

Velox binds directly to System.DateUtils.WeeksBetween. The installed routine converts each endpoint with System.SysUtils.DateTimeToTimeStamp, combines the timestamp date and time into an Int64 millisecond count, takes the absolute difference and performs integer division by seven days.

Edge cases and quirks

  • This routine is duration-based. Two values in different ISO weeks can still return 0, and a seven-day interval returns 1 regardless of weekday.
  • The millisecond timestamp path preserves valid pre-1899 chronology, unlike the raw subtraction used by WeekSpan.
  • TDateTime carries no timezone. Daylight-saving transitions are not consulted; values are compared as encoded wall-clock timestamps.
  • Free Pascal documents the same two-argument concept. Velox follows the installed Delphi conversion and rounding implementation.

Performance and concurrency

The calculation is constant-time integer arithmetic after two timestamp conversions. It allocates no objects and reads no shared Velox state.

Related entries

  • WeekSpan — returns fractional weeks but uses raw TDateTime subtraction.
  • WithinPastWeeks — compares this complete-week result with an inclusive limit.
  • DaysBetween — returns the equivalent complete-day distance.

External references

Created 2026-07-15