Access 2003 adding new record to record set problem

I have a MainForm, a subform within the MainForm, that displays records from a recordset bound to the MainForm.
I have fields ReviewFrequency, ProjectedReviewDate, ActualReviewDate, NextReviewFrequency.
The ActualReviewDate is a user input and the NextReviewFrequency is a user input.
On entering the NextReviewFrequency I want a new record added to the recordset where the ReviewFrequency field in the NEW record, is given the value of the NextReviewFrequency just entered and the ProjectedReviewDate in the NEW record is calculated from the NewReviewFrequency and the ActualReviewDate from the previous record.

Help would be appreciated.