Interest on Craig’s Notes Payable has been incurred, but not recorded or paid. The interest that has been incurred is calculated as principal multiplied by the interest rate multiplied by the time period ($8,000 x 10% x 1/12 = $66.66). Interest Expense of $66.66 must be recorded as an accrued expense and Interest Payable, a liability, recorded for the amount that Craig is obligated to pay later. So an adjusting entry is needed to bring accounts up to date at December 31.