Question

How to get the number of months between two dates in Pascal

Answer 1

program MonthsBetweenExample;

{$mode objfpc}{$H+}

uses
  SysUtils;

{
  Returns the number of complete months between two dates.

  Examples:
    2026-01-15 -> 2027-07-20 = 18
    2026-01-15 -> 2027-07-14 = 17
}
function GetMonthsBetween(startdate, enddate: TDateTime): Integer;
var
  StartYear, StartMonth, StartDay: Word;
  EndYear, EndMonth, EndDay: Word;
begin
  { Extract year, month, and day components }
  DecodeDate(startdate, StartYear, StartMonth, StartDay);
  DecodeDate(enddate, EndYear, EndMonth, EndDay);

  { Calculate the raw month difference }
  Result :=
    (EndYear - StartYear) * 12 +
    (EndMonth - StartMonth);

  { If the end day is before the start day,
    the last month is not complete }
  if EndDay < StartDay then
    Dec(Result);
end;

var
  startdate: TDateTime;
  enddate: TDateTime;
  months: Integer;
begin
  { YYYY, MM, DD }
  startdate := EncodeDate(2026, 1, 15);
  enddate   := EncodeDate(2027, 7, 20);

  months := GetMonthsBetween(startdate, enddate);

  WriteLn('Months between dates: ', months);
end.


(*
run:

Months between dates: 18

*)

 

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