The bank is the building where you save your income. With transferring the income on your bank account you earn Interest. This is very useful, because the more money you have in the bank, the more money you get as interest.
The interest will get calculated and paid daily. The interest is based upon the Commerce. You have all the time access to the savings on your bank account you can deposit or make a payout at any time
How do they get calculated?
At a rate of 7% and a account balance from 1.000.000 Money
Here, in the example the player gets 2916,67 $ per hour.
To the day that's 70.000$. There are no compounded interest calculated to it. This counts only if no Money was withdrawn from the account. It is also possible that the Interest Rate falls to 0%.