Making a future date as the default value in DateTime field

How can I go about displaying a date which is one week from the current date?

You just need to use a custom default date that adds 7 days from the current date. Please check this demo form. Here's a guide on how to do it:

1. Insert a "DateTime" field.

2. Click the "Default Date" and then select "Custom".

3. In the textbox, put 'today+7' and press the "OK" button. 
    today = current date
    +7 = add 7 days from the current date

This instruction can be found if you hover your pointer in the blue "information" icon.

Let us know if you have any questions. Thank you.