Thank you all.

I think I must have mistakenly initiated a conversation privately outside of
the group by replying instead of replying to the group, which isn't very
helpful for anyone else reading the thread. So I have added Pete's answer
below.

Andrew

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An alternative approach, which might make it easier to follow, is to give
the cell with the subtotal in it a name, e.g. "Total". Then your formula
would become:
=SUM(A1:A100) - Total
Another approach: If in the first subtotal cell you have used the formula:
=SUBTOTAL(9,A1:A34)
then for the other overall total you could use:
=SUBTOTAL(9,A1:A100)
and this will ignore any intermediate subtotals you might have in your
range.
Hope this helps.
Pete
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