This example shows how to add numbers together from within a repeater.

OnSave Formula

Below is the formula you need. XmlField1 should be the underlying database field for your repeater.

cast(XmlField1 as xml).value('sum(!Xpath!)', 'float')

Add a repeater xpath (use !Xpath! to insert in to formula)

In the below we are targeting NumberField1 as the underlying field for values you want to total. Please replace with your required number field database value. 

//RepeaterData/Repeat/*[@DatabaseValue="NumberField1"]/@Value

Adding extra conditions

If you need to restrict the totalled rows to ones where another field in the repeat is set to a specific value, the following format can be used:

//RepeaterData/Repeat[Data/@DatabaseValue="TextField1" and Data/@Value="example"]/Data[@DatabaseValue="NumberField1"]/@Value