foreach $key (sort keys %ytd ){ ... 

Seriously, i want to point out that anytime i see variables like $t1, $c1, ,$d1, etc., i try to remove these and use 'containers' instead. Here is my take on the problem:

use strict;

my (@stuff,$cust,$total);
my %ytd = (
   foo => { d1 => 1, d2 => 2, c1 => 3, c2 => 4 },
   bar => { d1 => 5, d2 => 6, c1 => 7, c2 => 8 },
   baz => { d1 => 9, d2 => 1, c1 => 2, c2 => 3 },
   qux => { d1 => 4, d2 => 5, c1 => 2, c2 => 4 },
);

foreach $cust (sort keys %ytd) {
   my @tot = map {
      $ytd{$cust}->{"d$_"} - $ytd{$cust}->{"c$_"}
   } 1..2;

   $total = do { my $t; $t += $_ for @tot; $t };
   @stuff = (
      $ytd{$cust}->{d1}, $ytd{$cust}->{c1}, $tot[0],
      $ytd{$cust}->{d2}, $ytd{$cust}->{c2}, $tot[1],
   );
   write;
}


format STDOUT =

@<<<<<<<<<<<<<<<<<<<<
$cust
@#####.##  @#####.##  @#####.##     @#####.##  @#####.##  @#####.##
@stuff
                                            @#####.##
                                            $total
.
[download]

Without knowing the problem, i can't really comment on your datastructure %ytd, but it might benefit you in terms of maintenance to combine each of the 'dN' and 'cN' pairs into one that contains an array. For example:

my %ytd = (
    foo => { d => [1,2], c => [3,4] },
    bar => { d => [5,6], c => [7,8] },
    baz => { d => [9,1], c => [2,3] },
    qux => { d => [4,5], c => [2,4] },
);
[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)