Such a filled card will be accepted as a deposit of one dollar either in opening an account or in adding to an existing account.
Deposits are not entered in a depositor's book, as is the usual practice of savings banks, but are evidenced by certificates issued in fixed denominations of $1, $2, $5, $10, $20, $50, and $100.

These bear interest, from the first day of the month next following that in which the deposit is made, at the rate of 2 per cent per annum for a whole year (interest is not paid for any fraction of a year).

Interest is not compounded, unless the depositor withdraws the interest and redeposits it, but simple interest continues to accrue annually on a certificate so long as it is outstanding, without limitation as to time.
By the end of the first year (1911) of operation the savings system held a balance to the credit of depositors of nearly $11,000,000; in the next year (1912) there was added to this about $17,000,000; in the next year (1913) about $12,000,000; and this average rate of one million dollars a month net addition to deposits has continued to the present (1916).

These funds are deposited in banks belonging to the federal reserve system, which must deposit with the Treasurer of the United States designated kinds of bonds (national, state, and municipal) as security and pay interest at the rate of 2-1/2 per cent on the amount of the deposits.

The one-half per cent difference between this rate and that paid to individuals goes far toward paying the expense of operating the system.
Provision is made for the issue of postal savings bonds in exchange for certificates issued in sums of $20 or multiples thereof up to $500.