I have a spreadsheet where I am trying to sum the totals month on month
depending on which month it is (i.e. as it is now August, I only want to sum
up to August and no further) I have begun my formula:

=IF($AF$1$AB$2,SUM(F4:AC4),IF($AF$1$Z$2,SUM(F4:A A4),IF($AF$1$X$2,SUM(F4:Y4),IF($AF$1$V$2,SUM(F4: W4),IF($AF$1$T$2,SUM(F4:U4),IF($AF$1$R$2,SUM(F4: S4),IF($AF$1$P$2,SUM(F4:Q4),0)))))))

$AB$2, $Z$2, etc. are the month/year (they are all 2 cells merged starting
from F2)
$AF$1 contains the formula "=TODAY()"
$F$4:$AC$4 is the sum of April to March, $F$4:$AA$4 is April to February etc.

The example above works fine - working back from March to September.

However, when I get to August and type this:

=IF($AF$1$AB$2,SUM(F4:AC4),IF($AF$1$Z$2,SUM(F4:A A4),IF($AF$1$X$2,SUM(F4:Y4),IF($AF$1$V$2,SUM(F4: W4),IF($AF$1$T$2,SUM(F4:U4),IF($AF$1$R$2,SUM(F4: S4),IF($AF$1$P$2,SUM(F4:Q4),IF($AF$1$N$2,SUM(F4: O4),0))))))))

I get an error on the final sum, SUM(F4:04).

Am I being really thick? Is there an easier way of doing it?

Many thanks in advance.