ACH prenote is the common short name for an ACH prenotification, a zero-dollar entry that an originator sends through the Automated Clearing House network to test a customer's routing and account numbers before the first live credit or debit. The two terms mean the same thing; "prenote" is the form used by payroll staff, billers and bank operations teams, while "prenotification" is the wording of the network's rules.
A prenote carries no money. The receiving bank checks that the account exists and can accept the type of entry, and replies only if something is wrong, either with an ACH return or with a notification of change giving corrected details. If nothing comes back within the waiting period set by the rules, the originator may start sending live entries.
Prenotes are optional, and because they add a delay of several days and do not confirm who owns the account, many companies now use faster methods of bank account verification, such as micro-deposit verification or instant checks through a data provider. The main entry describes the process, timing and limits in full.