Opening an account costs 50 berries. After this, up to 10,000 berries may be stored in the bank at once.
Berries stored in the bank also accrue interest. At every half-hour mark of the pause menu's timer, the bank calculates and adds interest to the account. The rate is 2-4% of the current balance per half hour. Interest is capped at 75 berries per half hour, which requires at least 1875 berries in the bank.
Deposits, withdrawals, and the time of account creation do not effect interest calculation or timing whatsoever.
- When examining the banker, Vi will note that she believes they'll run off with the money to a hot spring, referencing Millibelle, the banker from Hollow Knight. 
- Before the 1.1 patch, the Bank offered 3% and 6% interest. There was also no interest cap.