Mail merge formula

[mridley]

Hi all i'm after a little help?

I use Tas books 2 for my accounting etc. It uses Word to mail merge when producing invoices quotes etc, what i am trying to do is use a formula to calclate a 20% deposit based on the merge field "Total". however when i input the formula it calculates from that point instead of when the mail merge I.E once it has a figure.

Any help would be much appreciated

Regards