- substr: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$a = "2014-12-01";
$b = "2015-01-01";
$i = date("Y-m", strtotime($a));
while($i <= date("Y-m", strtotime($b))){
echo $i."\n";
if(substr($i, 5, 2) == "12")
$i = (date("Y", strtotime($i."-01")) + 1)."-01";
else
$i++;
}