Option 1: Perform a find for just records meeting this criteria and then summary fields that total these fields will report the correct totals.
Option 2: A relationship could be defined that only match to these records, then a Sum function or a reference to a summary field in the related table will produce the requested total.
Option 3: If you upgrade to FileMaker 12 or 13, you can use ExecuteSQL to get these totals.
Option 4: You can define a calculation field for each of these three fields such as:
IF ( ( DateField > Get ( CurrentDate ) AND ( DepositPaid = "yes" or balancePaid = "yes) ; BalanceAmount )
Then add a summary field to total up the value of this calculation field.
Thanks for that. I went Option 4. Worked a treat!