Sec. 6. As used in this chapter, "net contribution" of a party to a joint account as of any given time means the sum of:
(1) all deposits made by or for the party; minus
(2) all withdrawals made by or for the party that have not been paid to or applied to the use of any other party; plus
(3) a pro rata share of any interest or dividends included in the current balance.
The term includes any proceeds of deposit life insurance added to the account by reason of the death of the party whose net contribution is in question.