If you can set up a relationship that matches to the records for this customer that precede the first entry in your found set, the same script that does your Date Range search can use a calculation can compute the "balance forward" put it in a global field or variable and show this amount in the header.
If you use a running total summary field to show the account balance for each entry, you can replace it on your layout with a calculation field that adds the running balance to the balance forward amount.
Ok Thanks, I think 2nd one is better. Please provide cal. field details.
There is no "second one". I have only described a single solution here. The calculation uses the value computed and placed in the global field or variable to compute the needed value.
The actual calculation is quite simple:
RunningBalSummaryField + GlobalBalanceForwardField
if you use a field. Or it becomes:
RunningBalSummaryField + $$GlobalBalanceForwardVariable
The main details are in the process that you use to get the needed value into that global field or variable. I can't really spell out all the details for that without a more detailed understanding of how you have set up the fields in your table and whether a single table is storing transactions for more than one account and/or for more than one customer.