How to get a calculated default date value as filter prompt

Dear Colleagues,

I would need to get a calculated date as dafault value in a query filter promp.

I tried to use the token <%TODAY%> to set by default the current date and it works.

But I'd need to set 6 months before the current date as default value in the filter prompt. Any idea to get it?

I tried to set <%TODAY%> - 120 for example  but it's not working because I think the system is taking this as a DATE type value.

Thanks in advance!

Regards.
Martin