Mortgage-Backed Security (MBS) Fast Pay Haircut
The Formal Definition
The sudden valuation discount and collateral haircut acceleration applied by prime brokers and repo counterparties to premium agency mortgage-backed securities when a sudden drop in interest rates accelerates refinancing speeds (Constant Prepayment Rate / CPR), threatening bondholders with immediate par prepayment losses.
$$\text{Fast-Pay Haircut Markup} = \text{Base Haircut} + [ \gamma \times \max(0, \text{Realized CPR} - \text{Projected CPR}) ]$$
Cole Barrett's Reality Check
The Unvarnished Bottom Line"Buying a mortgage bond at $106 because it has a fat 6% coupon feels great until mortgage rates drop. When homeowners refinance, they don't buy your bond back at $106; they pay off their loan at $100 par. That premium you paid disappears overnight. When repo lenders see prepayments accelerating, they slap on a 'fast-pay haircut,' demanding more cash collateral to cover the evaporating bond premium."
Interactive Simulator: Test the Math
Real-World Example: Scenario Breakdown
Examining the real numbers for: Financing a $10,000,000 agency MBS portfolio purchased at a clean premium price of $105.00 during an aggressive interest rate cutting cycle
| Execution Metric | Prepayment-Protected MBS Allocator | High-Premium Generic MBS Holder |
|---|---|---|
| Fee / Rate | Institutional clearing rate | Institutional rate |
| Spread / Buffer | Invested in low-loan-balance or high-seasoned MBS pools that historically resist aggressive refinancing waves | Bought generic 'to-be-announced' (TBA) premium mortgage pools yielding a high headline coupon |
| Execution / Status | Prepayment speeds stayed stable at 8 CPR despite rate cuts; bond price appreciated smoothly with lower yields | Refinancing surged; prepayments spiked to 35 CPR; bond premium was wiped out as principal returned at par |
| Total Cost / Result | Protected capital and margin lines through prepayment-resistant pool selection | Suffered capital destruction and collateral margin calls from accelerated prepayments |
How Brokers Weaponize This Term
When analyzing mortgage REITs or fixed-income bond funds, review the portfolio's average 'Cost Basis relative to Par'. If a fund holds agency MBS purchased at prices above $103 during a rate-cutting cycle, accelerating prepayment speeds will trigger severe capital losses.
Broker Evaluation Matrix
Cole Approves
Charles Schwab: Provides institutional bond analytics displaying option-adjusted spread (OAS), prepayment models, and effective duration on mortgage debt.
Read Audit →Cole Flags / Avoids
High-Yield Advisory Wrap Programs: Allocates client capital into premium mortgage-backed debt funds strictly to show higher headline yield without disclosing prepayment risk.
View Trap Details →Frequently Asked Questions
What is the Constant Prepayment Rate (CPR)?
CPR is an annualized percentage metric that estimates the proportion of an MBS pool's principal outstanding that is expected to be prepaid early by homeowners.
Why do prepayments hurt premium bondholders?
Because if you pay $105 to buy a bond, and the homeowner refinances and pays off their mortgage early, the loan principal is returned to you at exactly $100 par, locking in an immediate $5 loss per bond.