Many checking and savings accounts require a minimum balance. Keep that amount in the account, and you avoid a monthly fee. Drop below it, and the bank charges you. The minimum might be $500, $1,500, or more. Some banks waive the requirement if you set up direct deposit or make a certain number of transactions. Others charge the fee regardless.

Minimum balance requirements are a pricing tool. Banks use them to discourage small, unprofitable accounts and encourage customers to consolidate their money. A customer with $10,000 in deposits is more valuable than one with $200. The bank can lend out the larger balance and earn more interest. Fees from small accounts are a secondary revenue source.

The rules vary widely. A basic checking account at a large national bank might require $1,500 to avoid a $12 monthly fee. An online bank might require nothing and charge nothing. A savings account might require $300 to avoid a $5 fee. Some accounts waive the minimum for students or seniors. The details are buried in the account agreement, which few customers read.

Minimum balances can be a trap for low-income customers. If you cannot maintain the balance, you pay fees that eat into what little you have. That is one reason consumer advocates push for no-fee accounts and why some cities have partnered with banks to offer low-cost alternatives. The account is free only if you can afford to keep money in it.