Diferencia, en meses entre dos fechas

[quimfv]

$d2 = 'YYYY-mm-dd'; <--- debes estar seguro que llega en este formato

$duracion = mysql_query("SELECT DATEDIFF(NOW(),".$d2.",) AS 'd1 - d2'");

Manual

DATEDIFF() returns expr1 – expr2 expressed as a value in days from one date to the other. expr1 and expr2 are date or date-and-time expressions. Only the date parts of the values are used in the calculation.

mysql> SELECT DATEDIFF('2007-12-31 23:59:59','2007-12-30');
-> 1
mysql> SELECT DATEDIFF('2010-11-30 23:59:59','2010-12-31');
-> -31