Which type of interest considers both principal and previously earned interest?

The type of interest that considers both the principal amount and any previously earned interest is compound interest. This means that interest is calculated not only on the original principal but also on the accumulated interest from previous periods. As a result, the overall amount of interest earned can grow significantly over time, reflecting the concept of earning "interest on interest."

In contrast, simple interest is calculated solely on the principal amount, meaning that it does not take into account any interest that has been previously added to the principal. The other options—net pay and windfall income—refer to different financial concepts that are not related to the calculation of interest on investments or loans. Net pay typically describes the amount of income that remains after deductions, while windfall income refers to unexpected or unearned financial gains.