Date matching time period ...

Below is code that should provide the functionality that you need; handles fiscal month <-> calendar month mapping, as well as determining the last friday of any month. You only need to set the FiscalYearStart var (1-12) to specify when the fiscal years starts, the rest of the functions will then make use of this.

Let me know if there are questions / problems
Russell

// Example usage
  // Fiscal year starts in July (July is first fiscal month)
  FiscalYearStart:=7;

  // Get the posting date for the 6th fiscal month (December)
  ShowMessage(DateToStr(GetPostingDate(6)));

  // Check that a given posting date is correct for the period that it falls in
  if IsValidPostingDate(StrToDate('3/28/2008')) then
     ShowMessage('Valid')
  else
     ShowMessage('Invalid');

  if IsValidPostingDate(StrToDate('2/21/2008')) then
     ShowMessage('Valid')
  else
     ShowMessage('Invalid');

-----------

unit GL_Example;
////////////////////////////////////////////////////////////////////////////////
//
//   Unit        :  GL_Example
//   Author      :  rllibby
//   Date        :  01.22.2008
//   Description :  Functions to check that a given date is correct for the
//                  posting period, as well as return the posting date for
//                  a given period. Also routines for changing a calendar month
//                  to a fiscal period, and vice versa.
//
////////////////////////////////////////////////////////////////////////////////
interface

////////////////////////////////////////////////////////////////////////////////
//   Include units
////////////////////////////////////////////////////////////////////////////////
uses
  Windows, SysUtils;

////////////////////////////////////////////////////////////////////////////////
//   Resource strings
////////////////////////////////////////////////////////////////////////////////
resourcestring
  resMonth          =  'Invalid calendar month specified';
  resFiscalMonth    =  'Invalid fiscal month specified';
  resFiscalYear     =  'Invalid fiscal year starting period';

////////////////////////////////////////////////////////////////////////////////
//   Date functions
////////////////////////////////////////////////////////////////////////////////
function   GetFiscalMonth(PostingDate: TDateTime): Word;
function   GetPostingDate(FiscalMonth: Word): TDateTime;
function   FiscalMonthToMonth(FiscalMonth: Word): Word;
function   MonthToFiscalMonth(Month: Word): Word;
function   IsValidPostingDate(PostingDate: TDateTime): Boolean;

////////////////////////////////////////////////////////////////////////////////
//   Determines the month (period) that the fiscal year starts on: valid 1-12
////////////////////////////////////////////////////////////////////////////////
var
  FiscalYearStart:  Word  =  1;

implementation

function GetFiscalMonth(PostingDate: TDateTime): Word;
var  wParts:        Array [0..2] of Word;
begin

  // Decode posting date to get the calendar month
  DecodeDate(PostingDate, wParts[0], wParts[1], wParts[2]);

  // Check posting date against calculated posting date for the period
  result:=MonthToFiscalMonth(wParts[1]);

end;

function IsValidPostingDate(PostingDate: TDateTime): Boolean;
var  wParts:        Array [0..2] of Word;
begin

  // Decode posting date to get the calendar month
  DecodeDate(PostingDate, wParts[0], wParts[1], wParts[2]);

  // Check posting date against calculated posting date for the period
  result:=(Trunc(PostingDate) = GetPostingDate(GetFiscalMonth(PostingDate)));

end;

function MonthToFiscalMonth(Month: Word): Word;
begin

  // Check month
  if not(Month in [1..12]) then raise Exception.CreateRes(@resMonth);

  // Check fiscal year start
  if not(FiscalYearStart in [1..12]) then raise Exception.CreateRes(@resFiscalYear);

  // Remap calendar month into fiscal period
  if (Month >= FiscalYearStart) then
     // Succesor of the difference
     result:=Succ(Month - FiscalYearStart)
  else
     // Subtract and add 12 to the difference
     result:=Succ(12 + (Month - FiscalYearStart));

end;

function FiscalMonthToMonth(FiscalMonth: Word): Word;
begin

  // Check period
  if not(FiscalMonth in [1..12]) then raise Exception.CreateRes(@resFiscalMonth);

  // Check fiscal year start
  if not(FiscalYearStart in [1..12]) then raise Exception.CreateRes(@resFiscalYear);

  // Remap fiscal period into calendar month
  if (Pred(FiscalYearStart + FiscalMonth) > 12) then
     // Handle month wrap
     result:=Pred(FiscalYearStart + FiscalMonth) mod 12
  else
     // No wrap
     result:=Pred(FiscalYearStart + FiscalMonth);

end;

function GetPostingDate(FiscalMonth: Word): TDateTime;
var  wParts:        Array [0..2] of Word;
     wDay:          Word;
begin

  // Decode current date to get the year
  DecodeDate(Now, wParts[0], wParts[1], wParts[2]);

  // Remap fiscal period into calendar month
  wParts[1]:=FiscalMonthToMonth(FiscalMonth);

  // We need to get the first day of the following month and subrtact one to get the last day for the period
  if (wParts[1] = 12) then
  begin
     // Increment the year
     Inc(wParts[0]);
     // Set month to one
     wParts[1]:=1;
  end
  else
     // Increment the month
     Inc(wParts[1]);

  // Set the day to first of month
  wParts[2]:=1;

  // Encode date and subtract one to get last day of month
  result:=EncodeDate(wParts[0], wParts[1], wParts[2]) - 1.0;

  // Check the day of week to figure out where the last friday of the month falls
  wDay:=DayOfWeek(result);

  // Handle the day to determine where friday is
  case wDay of
     // Sunday
     1  :  result:=result - 2.0;
     // Monday
     2  :  result:=result - 3.0;
     // Tuesday
     3  :  result:=result - 4.0;
     // Wednesday
     4  :  result:=result - 5.0;
     // Thursday
     5  :  result:=result - 6.0;
     // Friday
     6  :  ;
     // Saturday
     7  :  result:=result - 1.0;
  end;

end;

end.