Many banks require you to keep a minimum balance in your account in order to earn the maximum interest rate for a given statement cycle. (valuepenguin.com)
Interest is calculated by the average daily balance method, which applies a periodic rate to the average daily balance in the account for the period. (firstib.com)
Not only will he be penalized by his landlord, he will now have an available balance in his account of $ 650 - $ 30 = $ 620. (investopedia.com)