Consider the following:
- Ensure the report parameters include all applicable data values. If the data values expected to sum up are outside the report parameters, the totals will be incorrect.
- Use Running Totals instead of Summary fields as Running Totals give more control. In the Evaluate section of the Running Total, evaluate on the change of a field and use the ID or IDKEY for the field that you are summing.
- If using a DistinctCount and getting lower than expected numbers, consider using a Count instead. This may be filtering out records which may be appearing in multiple groups.