A php function that outputs a calendar for a given month and year. Optionally, a heading (e.g. weekdays) can be displayed, and the current day is highlighted. The calendar can be styled via CSS.

calendar.php

<?php
function drawCalendar($year, $month, $heading = null, $forceSixthRow = false) {
	$daysInMonth = date("t", mktime(0, 0, 0, $month, 1, $year));
	$daysInPrevious = date("t", mktime(0, 0, 0, $month-1, 1, $year));
	$weekdayOfFirst = date("N", mktime(0, 0, 0, $month, 1, $year)) - 1;
	$rows = ($forceSixthRow || $weekdayOfFirst + $daysInMonth > 35) ? 6 : 5;
	echo '<table class="calendar" border="1">';
	if($heading != null) {
		for ($i=0; $i < 7; $i++) { 
			echo '<th>'.$heading[$i].'</th>';
		}
	}
	for ($row=0; $row < $rows; $row++) { 
		echo '<tr>';
		for ($column=0; $column < 7; $column++) {
			$day = 7*$row + $column - $weekdayOfFirst + 1;
			if($day < 1) {
				$todayClass = date('Y-m-d') == date('Y-m-d', mktime(0, 0, 0, $month-1, $daysInPrevious + $day, $year)) ? ' current' : '';
				echo '<td class="inactive'.$todayClass.'">'.($daysInPrevious + $day).'</td>';
			} else if($day > $daysInMonth) {
				$todayClass = date('Y-m-d') == date('Y-m-d', mktime(0, 0, 0, $month+1, $day - $daysInMonth, $year)) ? ' current' : '';
				echo '<td class="inactive'.$todayClass.'">'.($day - $daysInMonth).'</td>';
			} else {
				$todayClass = date('Y-m-d') == date('Y-m-d', mktime(0, 0, 0, $month, $day, $year)) ? ' class="current"' : '';
				echo '<td'.$todayClass.'>'.$day.'</td>';
			}
		}
		echo '</tr>';
	}
	echo '</table>';
}
?>