Countif formula

I am trying to use a COUNTIF formula on an item so I can count how many Subitems have the status of “Complete” and show it at the Item level.

For example I you have an Item which contains 10 subitems. At the item level I want to be able to have a column that looks at the SubItems and tells me how many of them have been marked as Complete. I then want to be able to use that number to report in Board level graph of how many subitems are complete.