Without looking it is hard to say, it could be filters or it could be something like flat fees 

Could also be that slips were entered, but not yet billed. 

The A/R would reflect actually billed out values for the month, but don't necessarily reflect when the underlying slips for those bills were entered.

Caren is correct, flat fees or any other type of adjustment to the amount billed might be the culprit, but we'd really have to look at the two reports to be able to tell you anything.

I figured out what the difference was. Included under the fees for the monthly slip totals is a client that when we complete the slips we select no charge.  That amount was  $9,362.  Under the costs for the same client is an amount of $6,000. These do no show up on the A/R balances report because the fees were not actually billed and the $6,000 is already paid.  My next question is this.  My boss doesn't want the no charge fees to show up on the monthly slip total report.  How can I do this?

There should be a filter available on the report for slip billing status. That will allow you to include only billable slips.