You could use the computed field module.
Computed Field is a very powerful field module that lets you add a custom "computed fields" to your content types. These computed fields are populated with values that you define via PHP code. You may draw on anything available to Drupal, including other fields, the current user, database tables, you name it. (Feeling the power yet? :) ) You can also choose whether to store your computed field values in the database with other content fields, or have them "calculated" on the fly during node views. (Although you should note that Views use requires database stored values.) This field is literally the Swiss Army knife of fields. So start cooking up your PHP based values!
You can get all the information that you add in other fields with in the computed field. Since you have not yet saved the node you might want to add the following code at the beginning to make the nid available.
https://drupal.org/node/149225