Dates showing up wrong on 31st of the month.

In your original posted function you are sending something like '-1 months' and setting the variables:

PHP Code:

   $pm = (int) date('n', strtotime($month_num));
    $pmy = (int) date('Y', strtotime($month_num)); 


Where 'n' is 1-12 and 'Y' is full year like 2017.

So just change it to (and I am not sure if you mean by -1 months to include last month or just to cover the current month)

PHP Code:

$date = new DateTime('FIRST DAY OF '.$month_num);
$pm =  $date->format('n'); 
$pmy = $date->format('Y'); 


Nothing will have changed apart from your dates should all work now.

PS have not tested this just wrote it out so might be a bit buggy. In theory it is right.


Edit: Just tested it on phpfiddle and it is working fine, but can't remember my login so can't post a link :-)
Just paste this in and you will see it: http://phpfiddle.org/

PHP Code:

<?php
$month_num = '-1 months';

$date = new DateTime('FIRST DAY OF '.$month_num);
$pm =  $date->format('n'); 
$pmy = $date->format('Y'); 

echo $pm;
echo '<br />';
echo $pmy;

?>