Yet another way to do it...

use DateTime::Event::Recurrence;

my $now = DateTime->now;
my $weeks = DateTime::Event::Recurrence->weekly;

print $weeks->current( $now )->ymd,"\n";
print $weeks->next( $now )->ymd,"\n";

# output
2003-09-08
2003-09-15
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update: s/previous/current/