When an Opportunity is created in Salesforce CRM, the workflow rule checks that the Opportunity is open (that is, not set as closed) and, if so, the workflow field update is immediately triggered.

By checking for open opportunities only, we ensure that any historic closed opportunities that are imported or retrospectively entered are excluded from this workflow rule.

The workflow field update then sets the Close Date of the Opportunity to the current date and time plus 21 days.

As an example the current date is October 1st 2017; so, before saving the new opportunity shows October 1st 2017 in the Close Date, as shown in the following screenshot:

Upon saving, the new opportunity shows October 22nd 2017 in the Close Date, as shown in the following screenshot: