Your student loan interest reveals just how much you’re really paying for that college education. Here’s a step-by-step guide on how to calculate it.

Credit cards charge interest, known as APR, if you carry a balance past your due date. Here's a step-by-step guide on how to calculate your credit card interest.

Regardless of the number of days in the month, to calculate prorated rent, always divide the month's rent by 30. Then multiple this amount by the number of days a tenant is responsible for the rent.