A linked account instrument is used to access funds in an existing demand deposit account held at a financial institution. Merchant or other transactions are first processed against a demand deposit account via an electronic authorization network. If the demand deposit account does not have sufficient funds, the transactions may be processed as a credit charge against an designated credit account. The demand deposit account may subsequently be swept at predetermined times in search of funds to defray the overdraft. If adequate funds are present, they will be withdrawn from the demand deposit account, and the credit account will be cleared. Otherwise, the instrument holder's daily purchasing abilities may be temporarily suspended until the credit account is settled. The processing of overdraft amounts may be on a FIFO, smallest-first or other basis.