A DDA number is the account number of a checking account, or demand deposit account. A checking account and a DDA refer to the same financial instrument.
A check as issued by a bank features two number codes at the very bottom. The of 9-digit numbers to the left is known as the American Banker's Association number or bank routing number, used to identify the specific bank where the account is located. Beside it to the right is the DDA or checking account number, which is specific to each individual account.
Most consumer bank accounts or DDAs allow the owner to withdraw money at any time but in some instances may require a waiting period of a few days.
A NOW account is a different type. The acronym refers to a negotiable order of withdrawal account. This operates similar to a checking account held by a bank or credit union but a NOW account also accrues interest on the balance. In this case, the financial institution has the right to require 7 days notice before any withdrawal of funds. However, in practice this is seldom done.
While checking privileges are available on some other types of accounts, including money market funds and loan accounts, DDAs and NOW accounts are those typically chosen for everyday use by individuals.