Not sure what to call this but when invoicing clients in Germany, their invoices needs a field that shows the “Leistungsperiode” which roughly translates to the “period for which the invoice” applies.
i.e. for a periodical invoice like hosting, this would have a value of “01.07 - 31.07” or simply “the month of July”
What is the best method to show such a field in every invoice? If I create a custom field it looks like I can only enter a static value.
If you click the help icon to the right of the frequency select on the recurring invoice page you can see details about the supported date variables.
Thanks, that solves it and works fine in the item description field although I initially wanted to have that variable i.e. “:MONTH” in the header of the invoice grouped with the invoice number, invoice date, due date, etc. - I assume there is no way to get that working?
Not that I’m aware of, the date variables aren’t currently supported in custom fields.
We’ll look into it for a future release.
I think I found a workaround: create a custom field for invoices, make it a drop-down and list January-December as options 
This works for me.
Nice!
except it does not work for recurring invoices since its a “static” drop-down. damn. Please make a note of this feature on your wish list.
I double checked with someone working in the finance department in Germany, apparently this field could also be a “delivery date”