Date Entered+30 days

Date Entered+30 days

Hello, 

I'm trying to create a custom field under Quotes so that the day entered in the field, will automatically add 30 days to it, when it shows up on the Quote. Date Entered+30 days. Anyone know how to do this? 

I've not done this before, but from what I've read it's using Adddate? 

${Quotes.Valid Till}+Adddate(0,0,30,0,0,0) ??