I have a transactions table:
fldCustomerID
fldTransactionDte
fldDebitAmount
fldCreditAmount
fldTransDetails

I created a query with the custId,date, credits,debits.
From that I created a report with a text box with =[CreditAmount]-[DebitAmount]as the control source set running sum over all.

However the sum does not give me a proper balance. It looks like the sum is not calculating for every row. How can I amend this to work properly?

Thanks in advance for any answers u can give me.

Yes sorry I missed on the first post Customer ID should be the foreign key in your table add another field fldTrID and make autonumber, you should have seperate ID's for debits and credits even if they are both entered on the same date ,since you will have blank entries in both fields set default value to 0. If you have null field then use Nz in yor calculations ie.=Nz([Credits])-Nz([Debits]).
HTH