© 2012 Michael Thompson php Algorithm for Calculating Easter Holidays [ Main Index ]

Sample Implementation:

Holiday
Mardi Gras	Tue, Feb 21st
Ash Wednesday	Wed, Feb 22nd
Palm Sunday	Sun, Apr 1st
Maundy Thursday	Thu, Apr 5th
Good Friday	Fri, Apr 6th
Easter	Sun, Apr 8th
Quasimodo Sunday	Sun, Apr 15th
Rogation Sunday	Sun, May 13th
Ascension Thursday	Thu, May 17th
Pentecost	Sun, May 27th
Trinity Sunday	Sun, Jun 3rd
Corpus Christi	Thu, Jun 7th

Purpose:

To determine the date of the Easter holidays for a given year:

The date of Easter Day was defined by the Council of Nicaea in AD325 as the Sunday after the first full moon which falls on or after the Spring Equinox. The Equinox is assumed to always fall on 21st March, so the calculation reduces to determining the date of the full moon and the date of the following Sunday. The algorithm used here was introduced around the year 532 by Dionysius Exiguus. Under the Julian Calendar a simple 19-year cycle is used to track the phases of the Moon. Under the Gregorian Calendar (devised by Clavius and Lilius, and introduced by Pope Gregory XIII in October 1582, and into Britain and its then colonies in September 1752) two correction factors are added to make the cycle more accurate.

Method:

function tmEaster($year,$EasterDay=0)
{

################################################################
# if you have php v3.1 or greater use the following to get the
# value for Easter
#
# $rtn = mktime(0,0,0,3,21 + easter_days($year),$year);
#
# otherwise we need to do it the long way...
################################################################
  $golden = ($year % 19) + 1;
  if( $year <= 1752 )
  {
    # Julian calendar
    $dom = floor(($year + ($year/4) + 5) % 7);
    if( $dom<0 ) $dom += 7;

    $pfm = floor((3 - (11 * $golden) - 7) % 30);
  }
  else
  {
    # Gregorian calendar
    $dom = ($year + ($year/4) - ($year/100) + ($year/400)) % 7;
    if( $dom<0 ) $dom += 7;

    $solar = floor(($year - 1600)/100 - ($year - 1600)/400);
    $lunar = floor(((($year - 1400)/100) * 8) /25);

    $pfm = floor((3 - (11 * $golden) + $solar - $lunar) % 30);
  }
  if( $pfm<0 ) $pfm += 30;

  if( ($pfm==29) || ($pfm==28 && $golden>11) ) $pfm--;

  $tmp = floor((4 - $pfm - $dom) % 7);
  if( $tmp<0 ) $tmp += 7;

  $easter = $pfm + $tmp + (date("L",mktime(0,0,0,1,1,$year))!=0?0:1);

  if( $easter<11 )
  {
    $mo = 3;
    $da = $easter + 21;
  }
  else
  {  
    $mo = 4;
    $da = $easter - 10;
  }
  $rtn = mktime(0,0,0,$mo,$da,$year);
################################################################

  if( $EasterDay!=0 )
  {
    $mo = date("n",$rtn);
    $da = date("j",$rtn);

    switch( $EasterDay )
    {
      case 1:  # Palm Sunday
      $rtn = mktime(0,0,0,$mo,$da - 7,$year);
      break;
      case 2:  # $Mardi Gras
      $rtn = mktime(0,0,0,$mo,$da - 47,$year);
      break;
      case 3:  # Ash Wednesday
      $rtn = mktime(0,0,0,$mo,$da - 46,$year);
      break;
      case 4:  # Holy Thursday
      $rtn = mktime(0,0,0,$mo,$da - 3,$year);
      break;
      case 5:  # Good Friday
      $rtn = mktime(0,0,0,$mo,$da - 2,$year);
      break;
      case 6:  # Passover
      $rtn = mktime(0,0,0,$mo,$da - 6,$year);
      break;
      case 7:  # Pentecost
      $rtn = mktime(0,0,0,$mo,$da + 49,$year);
      break;
      case 8:  # Ascension
      $rtn = mktime(0,0,0,$mo,$da + (49 - 10),$year);
      break;
      case 9:  # Pentecost
      $rtn = mktime(0,0,0,$mo,$da + (49 + 7),$year);
      break;
      case 10:  # Rogation Sunday
      $rtn = mktime(0,0,0,$mo,$da + 35,$year);
      break;
      case 11:  # Corpus Christi
      $rtn = mktime(0,0,0,$mo,$da + (49 + 11),$year);
      break;
      case 13:  # Quasimodo Sunday
      $rtn = mktime(0,0,0,$mo,$da + 7,$year);
      break;
    }
  }
  return $rtn;
}