The option was released in theme version 2.0.5
A theme and core plugin updates will be required – help to update http://help.wpresidence.net/article/how-to-update-the-theme/
Clear theme, plugin and browser cache after update to see the new mortgage calculator.
The mortgage calculator exists for Default Property Template and can be turned on/off from Theme Options -> Design -> Property Page Settings
You can enable these 2 fields to be managed for each property in Front End -> Submit Listing form
And these 2 values can be modified per property from wp-admin as well (Properties -> Edit Propeprty-> Property Details)