Running total fields, although similar to summary fields, offer more control over how the total is calculated and when it is reset. Running total fields are particularly well suited to perform these totaling functions:
A running total field can be used on database fields and first-pass formulas, but cannot be used on second-pass formulas or formulas that reference other second-pass formulas.
Placement of Running Total Fields | Creating Running Totals in a List | Creating Running Totals for a Group | Creating Conditional Running Totals