Today is Class
 A Notification Day in the TBA Secondary Mortgage Market. Class A MBS coupons consist of Fannie Mae and Freddie Mac 30 year loan notes. 
The June FN 4.5 MBS coupon has now begun the settlement process. Before the 
end of the session, the FN 4.5 price will seem to fall from where it is 
currently priced at 102-14, all the way down to 102-01.

WHY???
The MBS coupons that determine rate sheet 
pricing are traded in the TBA MBS market. 
TBA = To be Announced
In the TBA MBS market, at the 
time a trade is made, buyers and sellers agree to a few specific terms 
like what coupon, the issuing agency (Fannie, Freddie, Ginnie), size of 
trade, and a buy/sell price....the actual pools of loans are NOT 
exchanged at the time of this commitment. Instead, the MBS buyer and the
 seller make an agreement to complete the transaction at a later date. 
In the MBS market this date is pre-determined; it is called SETTLEMENT
 DAY (clever name huh?). 
Agency MBS trading settles once a 
month. We've been watching the June FN30 4.5 MBS coupon trade since May 11, 2010. As of tomorrow morning, we'll be watching the July FN30 4.5 MBS coupon until July 12, 2010 (August coupons for 30 day locks).
We can 
actually watch forward pricing as much as three months ahead.
SEE:

Anyway...two
 days before the pre-scheduled settlement date, the MBS seller 
"notifies" the MBS buyer of the specific pools that they will deliver to
 satisfy the previously agreed upon terms of the trade.
This
 is Fannie Mae's guidance:
Forty-eight hours prior to 
settlement, pool information must be communicated to the Capital Markets
 Sales Desk's back office by phone (202-752-5384), facsimile 
(202-752-3439), or via EPN transmission. Delivery of pool information 
must take place by 3:00 p.m. eastern time. It is advisable that pool 
information is communicated early as phone lines, fax machines, and the 
EPN queues are extremely taxed as the 3:00 p.m. deadline approaches. If 
the transmission does not occur by 3:00 p.m., one day's fail will be 
incurred, despite the fact the information is residing in queue.
Then
 the MBS buyer reviews the pool information to ensure the seller has 
delivered loans that meet the agreed upon terms.  48 hours later, after 
being deemed to within "Good Delivery" guidelines, pool purchase funds 
are wired and the trade is complete (it goes deeper...this is the 
outline).
BUT WHY DO PRICES SEEM TO FALL WHEN WE ROLL FROM 
FRONT MONTH TO BACK MONTH COUPONS?
Today the front month is 
the June delivery coupon. The back month is the July coupon.
Prices
 don't really fall though. We just start watching the back month MBS 
coupon because the front month coupon has just entered into the 
settlement process.  The back month coupon price remains the same!
Below
 is the current July settlement FN 4.5 MBS coupon. It's bid at 102-01. 
This is where prices will "seem" to fall later this afternoon.
 
The main reason behind the price 
"DROP" is lost "time value of money".
Interest rates can be 
thought of in three ways..
- Required Rate of Return: this is the minimum amount of return an investor is willing to receive when making an investment.
 - Discount Rate: the rate used to determine the present value of future cash flows. When you loan someone money with the intention of being paid back in the future, you must place a value on how much of a premium you are losing by not spending that money right now. The discount rate is essentially how much you are charging to delay repayment until a future date.
 - Opportunity Cost: the value an investor passes up when choosing an alternate investment. You must earn enough interest when you loan someone money to compensate for the loss of income that you could have been earning by investing elsewhere.
 
LET ME POSE A QUESTION: Would you rather have $1.00 today or 
$1.00 tomorrow?
You would rather have $1.00 today! If you have 
$1.00 today you can invest it today...the fact you are investing 
today vs. tomorrow implies you are giving the asset more time to 
appreciate, more time to accumulate interest earned (ACCRUE).
To
 relate this concept to the MBS market---if you buy the June FN 4.5 
coupon, then your returns will begin accruing on June 1. If you buy the 
July coupon---your returns don't start accruing until July 1. That means
 you would have to wait 20 days (from today) for your money to start working for 
you.  Investing now, before the roll,  puts money to work now, or in today's case, on June 1.
Starting tomorrow, because the June coupon has entered into the
 settlement process, MBS investors will have to wait until July 1 to see
 their funds start working. To compensate for the lost Time Value of 
Money, investors demand higher MBS yields. This lost time value of money
 is represented  by lower back month MBS prices (in this case the July 
FN 4.5 coupon).
Note: to be clear, the previous owner has 
rights to the income (accrued interest) earned from while they owned the
 coupon. The price you pay to purchase the back month coupon includes 
the income the current owner has accrued while they owned the coupon. 
The buyer recovers the added premium when  the coupon payment is 
deposited in their account. This is called the 'clean price'...its the 
same way Treasuries trade.
Plain
 and Simple:  If you own the June FN 4.5 MBS coupon, then you 
are entitled to the coupon clips (income) paid in June. If you decided to
 wait and buy the July MBS coupon...then you have to wait until July for
 your investment to start accruing interest. To compensate for the lost 
"time value of money", investors demand higher yields, which is why 
prices fall when delivery rolls from front month to back month. (not including any profit earned from price movement)
This
 explains why 60 and 90 day locks are more expensive. The longer the 
lock commitment period, the more it costs the lender to hedge 
interest-rate volatility and fall out risk.

