T-SQL (SS2K8) :: Use Previous Month Data In Column As Following Months Data Different Column

I have a table with Million plus records. Due to Running Totals article, I have been able to calculate the Trial_Balance for all months.

Now I am trying to provide a Beginning Balance for all months and the Logic is the Beginning Balance of July would be the Trial_Balance of June. I need to be able to do this for multiple account types. So the two datasets that need to be included in logic is actindx and Calendar_Month.

For actindx of 2 and Calendar_Month of 2014-01-01The Trial_Balance_Debit is 19585.46 This would make the Beginning_Balance of actindx 2 and Calendar_Month of 2014-02-01 19585.46

I am trying to do some type of self join, but not sure how to include each actindx number differently.

Table creation and data insert is below.

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[TrialBalance](
[Trial_Balance_ID] [int] IDENTITY(1,1) NOT NULL,

[Code] ....