Difference between dates calculation not working
===

I have the following code which calculates the amount of 'borg' according to the difference in days. I echoe'd out my `$days`variable to check how many days the difference is. According to that, the difference I have for one particular day is 38 days. How come that when I echo `$borg`, it still displays the amount of 0 ? In this example, `$days = 38`.

    $vandaag = date($format, strtotime('today'));
	$verschil = $interval->d;
	$diff = strtotime($retourdatum) - strtotime($vandaag);
	
	$days = floor(($diff - $years * 365*60*60*24 - $months*30*60*60*24)/ (60*60*24));
	echo $days;
	if($days > 0)
	{
		$borg = 80;
	}
	if($days<0 && $days>-7)
	{
		$borg = 65;
	}
	if($days>-7 && $days<-14)
	{
		$borg = 50;
	}
	if($days>-14 && $days<-21)
	{
		$borg = 35;
	}
	if($days>-21 && $days<-28)
	{
		$borg = 20;
	}
	if($days>-28 && $days<-35)
	{
		$borg = 5;
	}
	else
	{
		$borg = 0;
	}