Of course it returns 100 days; your while loop simply increments through the $date counter -- there's never any logic to treat $date like a date.

I would suggest using Date::Calc to verify that $date is really a valid date, and I'm sure there's TIMTOWTDI.

here's a sample I whomped up off the top of my head:

while ($date <=$end_date) {
.
.
.
(manipulate data here)
.
.
.
($this_year, $this_month, $this_day) = ($date =~/(\d{4})(\d(2})(\d{2})
+/)
if (!checkdate ($this_year, $this_month, $this_day) {
  # a new month dawns
  $this_day=1; 
  if ($this_month ==12) {#did december just pass
    $this_year++;      
    $this_month=0;
  }
  $this_month++;  #add one to the month.
  $date = $this_year . $this_month . $this_day;
}
}
[download]

Note that there's a lot of improvement to be wrung from this -- the regexp to split the date and the concatenation to reform it could be removed by using just $this_year and  $this_month and $this_day, but this might require some other adjustments to your code. update : There's a function in Date::Calc called Add_Delta_YMD which does pretty much the same thing.