TBA Market & Dollar Rolls: Agency MBS Forward Trading & Settlement
The TBA market is the primary forward market for agency mortgage-backed securities. With over $250 billion in daily trading volume, it is one of the most liquid fixed income markets in the world. Understanding TBA mechanics, settlement conventions, and dollar rolls is essential for anyone trading or investing in agency pass-throughs.
What Is the TBA Market?
TBA stands for to-be-announced. In a TBA trade, the buyer and seller agree on six parameters at trade time: the agency issuer (Ginnie Mae, Fannie Mae, or Freddie Mac), the mortgage program type, the coupon rate, the face value, the price, and the settlement date. However, the specific mortgage pools to be delivered are not specified until shortly before settlement.
TBA trades function like forward contracts for agency MBS. The buyer knows what type of security they will receive, but not which specific pools — giving the seller flexibility in what to deliver.
This “generic” trading convention creates tremendous liquidity. Because any eligible pool can satisfy the trade, market makers can quote tight bid-ask spreads without holding inventory of every specific pool. Mortgage originators use the TBA market to hedge pipeline risk before loans are even closed, locking in prices for MBS they will create in the future.
TBA Settlement Conventions
TBA trades settle on standardized monthly dates established by SIFMA (the Securities Industry and Financial Markets Association). The settlement schedule groups trades by coupon and agency program, with most agency pass-throughs settling between the 11th and 25th of each month.
Two business days before settlement (by 3:00 PM EST), the seller must notify the buyer of the specific pool numbers being delivered. This notification is called the call-out or 48-hour day. Until then, the buyer only knows the general characteristics of the security.
The 48-hour notification gives the buyer time to prepare for settlement but provides limited opportunity to reject pools. As long as the delivered pools meet good delivery guidelines, the buyer must accept them.
TBA Eligibility Requirements
Not all MBS can trade TBA. Eligibility is restricted to:
- Agency pass-throughs only — Ginnie Mae, Fannie Mae, and Freddie Mac single-class securities
- Standard coupon increments — typically 0.5% steps (e.g., 5.0%, 5.5%, 6.0%)
- Standard maturities — 30-year, 20-year, 15-year, and 10-year original terms
- Fixed-rate only — adjustable-rate mortgages (ARMs) trade specified pool, not TBA
CMOs, stripped MBS, and non-agency securities do not trade TBA. Their heterogeneous structures make generic trading impractical.
Good Delivery Guidelines
SIFMA establishes good delivery rules that define what the seller can deliver against a TBA trade:
| Guideline | Requirement |
|---|---|
| Pool count | Maximum 3 pools per $1 million face value traded |
| Variance tolerance | Delivered amount within 0.01% of trade face value |
| Coupon match | Delivered pools must have the exact coupon traded |
| Maturity match | Pools must match the original term (30-year, 15-year, etc.) |
| Agency match | Pools must be from the same issuer (GNMA, FNMA, or FHLMC) |
The tight 0.01% variance tolerance eliminates the old delivery option that sellers once had. Historically, sellers could deliver up to 3% more or less than the trade amount, creating an embedded option favoring the seller. Today’s tighter rules make TBA pricing more straightforward.
Dollar Rolls
A dollar roll is a specialized form of collateralized financing unique to the MBS market. It is economically similar to a repurchase agreement (repo), but with a critical difference.
In a repo, the borrower must return the identical securities. In a dollar roll, the borrower returns substantially identical securities — same coupon and issuer, but potentially different pool numbers.
Here’s how it works: a portfolio manager sells MBS for near-month settlement and simultaneously agrees to buy back substantially identical MBS for far-month settlement. The dealer provides 100% financing (no margin required) because the dealer retains flexibility in what pools to return. The dealer also keeps all coupon payments and principal payments (both scheduled and prepayments) during the roll period.
Roll Specialness
When the implied financing rate on a dollar roll is significantly below prevailing repo rates, the roll is said to be special. Roll specialness typically occurs when:
- Dealers need specific coupons to cover short positions
- Strong TBA demand creates a shortage of deliverable pools
- Month-end balance sheet constraints reduce dealer willingness to hold inventory
A hot roll (highly special) can imply financing rates near zero or even negative, making dollar rolls an attractive funding alternative for MBS investors.
Roll Analysis
The price difference between the near-month sale and the far-month repurchase is called the drop. When the yield curve is positively sloped, the repurchase price is typically lower than the sale price — the drop is positive.
The six key elements for analyzing roll economics are:
- Sale price and repurchase price — the drop
- Coupon payment forfeited — the dealer keeps the monthly interest
- Scheduled principal payments — the dealer receives these
- Projected prepayments — uncertain, requires assumption
- Attributes of the returned security — may differ from original pools
- Delivery variance — within the 0.01% tolerance
Dollar roll financing costs can only be estimated, not known precisely, because prepayments are uncertain and the returned pools may have different characteristics. Always perform sensitivity analysis across a range of prepayment assumptions.
Stipulated Trades (Spec Pools)
Stipulated trades (also called spec pool trades) add specific requirements beyond standard TBA terms. The buyer pays a premium — called a pay-up — to receive pools with particular characteristics.
Common stipulations include:
- Low loan balance (LLB) — pools with average loan balances below a threshold (e.g., $150,000); these prepay slower
- High LTV — loans with loan-to-value ratios above 95%; refinancing is harder
- New production — recently originated loans with predictable seasoning ramps
- Geographic concentration — pools from states with slower prepayment patterns
- Investor loans — non-owner-occupied properties with different prepayment behavior
Spec pool pay-ups fluctuate based on interest rate levels and prepayment expectations. In low-rate environments where fast prepayments threaten premium MBS, call-protected pools command higher pay-ups.
TBA Fails
A TBA fail occurs when the seller does not deliver the securities by the settlement date. Fails can be operational (back-office processing delays) or strategic (intentional when rolls are extremely special).
To discourage strategic fails, SIFMA imposes a fails charge. When the fed funds target rate exceeds 3%, the fails charge equals the greater of 3% minus the fed funds rate or zero, applied daily to the face value of the failed trade.
The fails charge creates an economic penalty for not delivering. However, when rolls are extremely special (implied financing rates well below the fails charge), failing can still be cheaper than rolling — though it damages counterparty relationships and can trigger margin calls.
How to Analyze Dollar Roll Economics
A portfolio manager sells $10 million par of Ginnie Mae 6.0% at 101-08 (101.25) for near-month settlement and agrees to repurchase at 101-00 (101.00) for far-month settlement.
| Component | Calculation | Value |
|---|---|---|
| Sale proceeds | $10M × 1.0125 | $10,125,000 |
| Drop (price difference) | 8/32 = 0.25% | $25,000 |
| Coupon forfeited | 6.0% × $10M / 12 | $50,000 |
| Principal offset (est.) | Scheduled + prepay @ 200 PSA | $2,500 |
| Net financing cost | $50,000 – $25,000 – $2,500 | $22,500 |
| Monthly rate | $22,500 / $10,125,000 | 0.222% |
| Annualized rate | 0.222% × 12 | 2.67% |
If repo financing for agency MBS is available at 4.5%, this roll offers a 183 basis point funding advantage. The roll is special, and the portfolio manager should prefer rolling to repo financing.
TBA vs Specified Pool Trading
TBA Trading
- Highest liquidity, tightest spreads
- Buyer accepts delivery uncertainty
- No pay-up premium
- Subject to cheapest-to-deliver (CTD) risk
- Best for: hedging, broad MBS exposure, short-term trading
Specified Pool Trading
- Lower liquidity, wider spreads
- Buyer knows exact pools received
- Requires pay-up premium
- Eliminates adverse selection risk
- Best for: buy-and-hold, prepayment-sensitive strategies
Limitations
Cheapest-to-deliver adverse selection: In TBA trades, sellers deliver pools that are least valuable to them — typically the slowest-paying, highest-extension-risk pools. Buyers systematically receive worse-than-average collateral.
Roll economics uncertainty: Dollar roll implied financing rates depend on prepayment assumptions that may prove incorrect. Fast prepayments when holding premium MBS reduce the principal offset benefit and increase effective financing costs.
Fails friction: During periods of extreme roll specialness, settlement fails can cascade through the market, disrupting hedging programs and creating operational burdens.
No granular control: TBA trading sacrifices prepayment and collateral visibility for liquidity. Investors with specific duration targets or cash flow requirements may find TBA exposure difficult to manage precisely.
Common Mistakes
1. Ignoring cheapest-to-deliver dynamics: Assuming TBA prices reflect average pool quality rather than CTD pool quality leads to overpaying for generic MBS exposure.
2. Conflating roll economics with carry: A hot roll (low implied financing) is not the same as positive carry. The all-in return depends on both the funding cost and the expected price change of the MBS.
3. Assuming all agency MBS trade TBA: Only fixed-rate agency pass-throughs with standard coupons and maturities are TBA-eligible. CMOs, IOs, POs, ARMs, and non-agency MBS trade specified pool only.
4. Comparing dollar roll rates to repo without adjustment: Dollar rolls involve substantially identical (not identical) return and prepayment risk transfer. A lower dollar roll rate does not always mean cheaper financing after accounting for these differences.
5. Underestimating fails risk: Strategic fails may seem profitable in extremely special rolls but can damage trading relationships and trigger margin calls that outweigh the savings.
Frequently Asked Questions
Disclaimer
This article is for educational and informational purposes only and does not constitute investment advice. TBA market conventions and dollar roll economics are subject to change. Example calculations use hypothetical values and estimated prepayment assumptions. Always consult current SIFMA guidelines and conduct your own analysis before trading.
