Return Array of Months Between and Inclusive of Start and End Dates

Question

I have two dates - a start date and an end date. I need to return an array of months ('Y-m' format) which includes every month between start and end date, as well as the months that those dates are in. I've tried:

$start = strtotime('2010-08-20');
$end = strtotime('2010-09-15');
$month = $start;
while($month <= $end) {
  $months[] = date('Y-m', $month);
  $month = strtotime("+1 month", $month);
}

The problem is that, in the above example, it only adds '2010-08' to the array, and not '2010-09'. I feel like the solution should be obvious, but I just can't see it.

Note that this should take into account situations like:

$start = strtotime('2010-08-20');
$end = strtotime('2010-08-21');
// should return '2010-08'

$start = strtotime('2010-08-20');
$end = strtotime('2010-09-01');
// should return '2010-08,2010-09'

$start = strtotime('2010-08-20');
$end = strtotime('2010-10-21');
// should return '2010-08,2010-09,2010-10'

Also, the version of PHP on my host is 5.2.6 so it has to work within those confines.

---

The solution I used was based on the answer below re. setting $start to the first day of the month. However I couldn't get it working with just the strtotime() and instead had to use another function I found on the web.

function firstDayOfMonth($uts=null) 
{ 
    $today = is_null($uts) ? getDate() : getDate($uts); 
    $first_day = getdate(mktime(0,0,0,$today['mon'],1,$today['year'])); 
    return $first_day[0]; 
}

$start = strtotime('2010-08-20');
$end = strtotime('2010-09-15');
$month = firstDayOfMonth($start);
while($month <= $end) {
  $months[] = date('Y-m', $month);
  $month = strtotime("+1 month", $month);
}

Answer 1

The problem is that $start day is bigger than end day, so after you add month to start its bigger than end, solution is to use first day of the month, like 2010-08-01 so after you add +1 month you will get at least equal $end ;)

Answer 2

This should do what you need.

$start = strtotime('2010-08-20');
$end = strtotime('2010-10-15');
$month = $start;
$months[] = date('Y-m', $start);
while($month <= $end) {
  $month = strtotime("+1 month", $month);
  $months[] = date('Y-m', $month);
}

Answer 3

Add a

if( date('d',$month) != date('d',$end) )
   $months[] = date('Y-m', $month);

below the loop. This means, you add the last month if its only partially contained in $end (days are different: last difference is smaller than a month).

rbo