When an actual/actual remittance type mortgage loan is repurchased, Fannie Mae is due interest from the LPI date up to, but not including, the repurchase date. However, when a scheduled/actual or a scheduled/scheduled remittance type mortgage loan is repurchased, Fannie Mae is due a full month of interest in all cases. A full month of interest will be based on a 360-day year, while a partial month's interest will be based on a 365-day year. The following table provides additional instructions for calculating the repurchase interest due Fannie Mae based on the remittance type of the mortgage loan.
For more information see Investor Reporting Manual Chapter 2-04, Reporting Specific Payment Transactions to Fannie Mae (02/14/2018)