calc time elapsed in days

[raphael()]

Hi,

I have to code a script to calc time elapsed in days as to calc the rent to
be charged.
The person would write an object number and date in a text file like

db.txt
OBJECT_NUM, DATE_GIVEN

2525,25.11.2008
2526,01.01.2009
2527,26.11.2009

Now when he enter "OBJECT_NUM" I have to tell him the numbers of days
elapsed since "DATE_GIVEN"
and the rent he should charge which increases every 15 days like

first 15 days = 2
next 15 days = 3
next 15 days = 5
next 15 days = 8
next 15 days = 10
now its always 10

So if the OBJECT is returned in say 40 days the rent charged is 10 (2 + 3 +
5)

Being a beginner, I thought of hard coding the values in the code.

    if ( $days_elapsed <= 15 ) {
        $total_cost = 2;
    } elsif ( $days_elapsed <= 30 ) {
        $total_cost = 5;
    } elsif ( $days_elapsed <= 45 ) {
        $total_cost = 10;
    } elsif ( $days_elapsed <= 60 ) {
        $total_cost = 18;
    } elsif ( $days_elapsed <= 75 ) {
        $total_cost = 28;
    } elsif ( $days_elapsed <= 90 ) {
        $total_cost = 38;
    } else {
        print "More than 90 days! SPECIAL RATE\n";
        exit;
    }


HOW CAN I COUNT ELAPSED DAYS ?

I tried in localtime() days value like

my @array_date = localtime();
my $current_dayofyear = @array_date[7];


But this would break on New year as "$current_dayofyear" would be reset.


SO HOW CAN I COUNT ELAPSED DAYS IF THE DATE FORMAT IS  01.01.2009?