or "generic" 30-year pools (issued by Fannie Mae, Freddie Mac, or Ginnie Mae) with coupons of 3.5–7%, one can see the prices posted on a TradeWeb screen by the primaries called To Be Allocated (TBA). This is due to the actual pools not being shown. These are forward prices for the next 3 delivery months since pools have not been cut; only the issuing agency, coupon, and dollar amount are revealed. A specific pool whose characteristics are known would usually trade "TBA plus {x} ticks" or a "pay-up", depending on characteristics. These are called "specified pools", since the buyer specifies the pool characteristic he/she is willing to "pay up" for. The price of an MBS pool is influenced by prepayment speed, usually measured in units of CPR or PSA. When a mortgage refinances or the borrower prepays during the month, the prepayment measurement increases. If an investor has acquired a pool at a premium (>100), as is common for higher coupons, then they are at risk for prepayment. If the purchase price was 105, the investor loses 5 cents for every dollar prepaid, which may significantly decrease the yield. This is likely to happen as holders of higher-coupon mortgages can have a larger incentive to refinance. Conversely, it may be advantageous to the bondholder for the borrower to prepay if the low-coupon MBS pool was bought at a discount (<100). This is due to the fact that when the borrower pays back the mortgage, he does so at "par". If an investor purchases a bond at 95 cents on the dollar, as the borrower prepays the investor gets the full dollar back, increasing their yield. However, this is less likely to occur, as borrowers with low-coupon mortgages have lower, or no, incentives to refinance. The price of an MBS pool is also influenced by the loan balance. Common specifications for MBS pools are loan amount ranges that each mortgage in the pool must pass. Typically, high-premium (high-coupon) MBSs backed by mortgages with an original loan balance no larger than $85,000 command the largest pay-ups. Even though the borrower is paying an above market yield, he or she is dissuaded from refinancing a small loan balance due to the high fixed cost involved. Low Loan Balance: < $85,000Mid Loan Balance: $85,000–$110,000High Loan Balance: $110,000–$150,000Super High Loan Balance: $150,000–$175,000TBA: > $175,000 The plurality of factors makes it difficult to calculate the value