I.e.
Month Returns
January 1
February 2
March 3
April 4
May 5
June 6
July 7
August 8
September
Depending on your scenario probably the most efficient solution to this would be to create an associative array like:
$months = array("january" => 1, "february" => 2, "march" => 3, "april" => 4, "may" => 5, "june" => 6, "july" => 7, "august" => 8, "september" => 9, "october" => 10, "november" => 11, "december" => 12);
And then your lookups are super easy:
$month = "Nobember";
$monthNumber = $months[strtolower($month)];