Calculated Date


I want to use recurring invoice and send those invoice on a yearly base to my customers.
I the invoice there is a webhosting abo.

The recurring invoice should display the period for the abo.

So The invoice send (as an example) in 2018 should say:

Abo from 01-03-2018 to 01-03-2019

The Invoice send in 2019 should say:

Abo from 01-03-2019 to 01-03-2020

I send the invoice 60 days before the start of the new period so I was thinking to use in the e-mail template somthing like:

`The invoice is for the period  {{{{invoice_date_created}}} + 60}.`

Is there a way to calculate the date value or does anyone have any suggestions how to solve my problem