Paying interest on a credit card does not help build a credit score. The money goes to the card issuer as the cost of borrowing, while credit scoring models focus on information such as payment history, balances and how much available credit you use.
Yet the belief persists that carrying a balance proves someone uses credit responsibly. That idea can turn into an expensive habit, especially for someone who deliberately leaves $20, $50, or $100 unpaid each month because they think the interest charge somehow earns credit-building points.
