How to create schedule date for next due date for payment

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SQL

I need to be able to provide a report with a next due date for payment date. The user is able to see next due date for payment. This can be done by specifying the frequency (daily, weekly, monthly,yearly), a "multiplier" (i.e. every 3 days, every 2 weeks, every 6 months, etc...) and a start date must be supply from the front end to the SQL. After the calculation I want it to insert the records into a scheduleTable which presented the user as a report. Example for schedule table

Create Table ScheduledDate
(
	LoanID SmallInt Not Null,
	LenderName Varchar(30)Not Null,
	ScheduledDates DateTime Not Null
) 


Create Proc prcCalculateScheduleDate
(
    @LoanID SmallInt,
    @StartDate DateTime,
	@EndDate DateTime
)
As
Begin
    Select 0 n, LOANID,REPAYMENT_STARTDATE,Frequency,Multiplier From LOANS_REPAYMENT_PLAN
    Where  LOANID = @LoanID AND REPAYMENT_STARTDATE=@StartDate AND REPAYMENT_ENDDATE = @EndDate
 
    Begin
    Select n+1 n,
        Case[Frequency]
            When 'Daily' Then DateAdd(Day,Multiplier,ScheduleDate)
            When 'Weekly' Then DateAdd(Week,Multiplier,ScheduleDate)
            When 'Monthly' Then DateAdd(Month,Multiplier,ScheduleDate)
            When 'Yearly' Then DateAdd(Year,Multiplier,ScheduleDate) 
    End As ScheduleDate,
       [Frequency],
       [Multiplier]
    From LOANS_REPAYMENT_PLAN
    Insert Into  ScheduledDate
	Group By  LOANID,LENDER_NAME
 End

Any help will be appreciated. NanaKwame