Interest expense is the cost of debt that has occurred during a specified period of time.
To illustrate interest expense under the accrual method of accounting, let's assume that a company borrows $100,000 on December 15 and agrees to pay the interest on the 15th of each month beginning on January 15. The loan states that the interest is 1% per month on the loan balance. The interest expense for the month of December will be approximately $500 ($100,000 x 1% x 1/2 month). The interest expense for the month of January will be $1,000 ($100,000 x 1%).
Since interest on debt is not paid daily, a company must record an adjusting entry to accrue interest expense and to report interest payable. Using our example above, at December 31 no interest was yet paid on the loan that began on December 15. However, the company did incur one-half month of interest expense. Therefore, the company needs to record an adjusting entry that debits Interest Expense $500, and credits Interest Payable for $500.