In CRM/potentials how can be done automating a date from another date?

In CRM/potentials how can be done automating a date from another date?

We have the field estimated closure date - we want to set-up another date field estimating another date related with production/delivery - this date is estimating counting 30 days from the estimated closure date - so I want this date to be set-up automatically from the estimated closure date... how can I do this?