Fannie Mae's present yield differential adjustment policy and a history of the various yield differential adjustment policies that may apply to mortgage loans are dependent on whether the mortgage loan is a fixedrate mortgage loan, an ARM loan, or a coop share loan.
Provisions for FixedRate Mortgage Loans: The following table describes the historical yield differential adjustment policies for fixedrate mortgage loans, except for coop share loans.
Date of Commitment  Terms of Provision 

June 22, 1981 to Fannie Mae investor reporting system conversion date^{1} 
Gross Yield Commitment: The servicer and Fannie Mae each retain onehalf of the first 0.25% excess. After that, the servicer retains onefourth of any other excess and Fannie Mae retains threefourths. Net Yield Commitment: After the excess is reduced by a minimum servicing fee of 0.375%, the remaining excess is shared under the same formula as shown above. 
Fannie Mae investor reporting system date^{1}to present 
The servicer retains all excess yield. 
Provisions for ARM Loans: The following table describes the historical yield differential adjustment policies for ARM loans, except for coop share loans.
Date of Commitment  Terms of Provision 

August 15, 1983 to September 10, 2017^{1} 
If Fannie Mae purchased the mortgage loan at par, the servicer retains until the first interest rate change any excess above the difference between the net mortgage rate and Fannie Mae's required yield. After that, the servicer may retain the amount by which the net mortgage margin^{2} exceeds Fannie Mae's required margin. If Fannie Mae purchased the mortgage loan at a discount, the servicer retains until the first interest rate change any excess above the difference between the net mortgage rate and Fannie Mae's required yield. After that, the servicer receives no excess. 
On and after September 11, 2017  For whole loans, at rate reset the lender passthrough rate must be calculated using the topdown method of calculation. See, 502, Calculations Related to Passthrough Rates in Fannie Mae’s Investor Reporting Manual for additional information regarding this calculation method. 
Provisions for Coop Share Loans: The following table describes the historical yield differential adjustment policies for coop share loans.
Date of Commitment  Terms of Provision 

May 11, 1984 through August 26, 1984 
The servicer retains all excess yield for ARM loans. After the excess for a fixedrate mortgage is reduced by a minimum servicing fee of 0.375%, the remaining excess is shared as follows:

August 27, 1984 to September 10, 2017 
For both ARM loans and fixedrate mortgage loans, the servicer retains all excess yield. 
On and after September 11, 2017  For ARM whole loans, at rate reset the lender passthrough rate must be calculated using the topdown method of calculation. See, 502, Calculations Related to Passthrough Rates in Fannie Mae’s Investor Reporting Manual for additional information regarding this calculation method. 
Related Announcements
The following table provides references to Announcements that are related to this topic.
Announcements  Issue Date 

Announcement SVC201707  August 16, 2017 
The date that the mortgage seller was converted to the Fannie Mae investor reporting system. The dates that the Fannie Mae regional offices implemented the Fannie Mae investor reporting system are: Atlanta, November 26, 1984; Chicago, December 3, 1984; Dallas, December 3, 1984; Pasadena, December 10, 1984; and Philadelphia, November 5,1984.
Different provisions apply for any interest ratecapped ARM plan mortgage loans delivered under commitments dated on and after February 19, 1985. Under those provisions, the servicer retains until the first interest rate change any excess above the difference between the net mortgage rate and Fannie Mae's required yield. The net mortgage rate is determined by subtracting the 0.5% minimum servicing fee from the mortgage interest rate. Then, on each interest rate change date, the servicer is allowed to retain the amount by which the new net mortgage rate exceeds Fannie Mae's new required PTR. The required PTR is determined by adding the net required margin to the index value, and then comparing the result to the maximum allowable required yield that was determined for both the peradjustment and lifetime interest rate limitations when Fannie Mae purchased the mortgage. If the calculated PTR exceeds the maximum allowable required yield, that yield becomes the PTR
The net mortgage margin is determined by subtracting the 0.5% minimum servicing fee from the margin specified in the mortgage instrument.