Interest that is earned from a mortgage or other loan with closed-end installments that contain a nonstandard payment period. In most cases, the additional interest is added on to the first payment. All remaining payment periods are uniform, assuming the loan has fixed payments and amortizes fully.
Also referred to as "interim interest."
An example of when odd-days interest is paid is when a mortgage begins in the middle of a month. For example, suppose you get a mortgage on September 20th; you would pay 10 days' worth of interest to cover the days to the beginning of October.