1. Login to your domain registrar (Ex: Godaddy)
Click on manage to enter your domain control panel.
2. Select the domain you want to create the sub domain for.
3. Click on "manage" under Forwarding -> Sub Domains
4. Create the new subdomain
Click on "Add subdomain forwarding"
5. Enter forwarding details
Under "Subdomain", enter the subdomain that you'd like to create for your Outgrow quiz or calculator
Under "Forward to", enter the URL of your calculator (without https://).
Under "Redirect type", select "301 (Permanent)"
Under "Forward settings", select "Forward with masking"
And that should be it! After a few minutes, you should be able to find your calculator on your new sub domain.