How do you calculate interest if you borrow money?

To calculate interest on a loan, you typically use the formula: Interest = Principal × Rate × Time. The principal is the amount borrowed, the rate is the annual interest rate expressed as a decimal, and time is the duration the money is borrowed for, usually in years. For example, if you borrow $1,000 at a 5% annual interest rate for 3 years, the interest would be $1,000 × 0.05 × 3 = $150. Depending on the type of interest (simple or compound), the calculation may vary slightly.