How banks express overdraft cost
Banks generally treat an overdraft facility like a short-term loan. The advertised charge is usually an annual percentage rate (APR) for arranged overdrafts or fixed per-item fees for unarranged items. For arranged overdrafts the bank converts the APR into a daily interest rate and applies that rate to the overdrawn principal. Regulatory and consumer guidance from the Consumer Financial Protection Bureau and the Federal Deposit Insurance Corporation describe these two common approaches and outline transparency expectations. Practices differ by country and product.
The basic calculation method
When interest applies, the typical formula is simple: the daily interest equals the negative balance multiplied by the APR divided by 365. The bank records the negative balance each day, multiplies by APR/365, and sums those daily charges over the billing cycle to create the interest posted to the account. Some banks use 360 days for convenience, and some compound daily interest so that previously charged interest increases subsequent daily balances. Banks disclose the exact method in account terms and periodic statements.
Fees, timing and additional charges
Unarranged overdrafts are often handled differently: instead of—or in addition to—interest, banks may charge a fixed fee per transaction or a daily fee while the account remains negative. Overdraft fees can exceed the equivalent APR for small, short-lived overdrafts, while arranged overdrafts priced as interest typically become cheaper the longer the balance persists. The Consumer Financial Protection Bureau emphasizes that fee-driven structures create different incentives for consumers and institutions.
Causes, consequences and social context
Overdrafts arise from timing mismatches between payments and deposits, holds placed by merchants, or deliberate borrowing. Consequences include consumer financial strain, cascading fees, and reputational risk for banks. Research and regulatory reviews by the Consumer Financial Protection Bureau and the Federal Deposit Insurance Corporation highlight that fee-heavy overdraft models disproportionately burden low-income households and can deepen financial exclusion. In some cultures and territories, overdrafts function as an accepted short-term credit tool; in others, regulatory regimes like those overseen by the Financial Conduct Authority in the United Kingdom impose stricter price and disclosure rules. Understanding the precise bank terms is essential for consumers to compare real cost and risk.