Eurodollar / SOFR Convexity Bias
The Formal Definition
The structural pricing divergence between forward rate agreements (FRAs) and interest rate futures contracts (such as SOFR or legacy Eurodollars), driven by the daily mark-to-market margin settlement of futures that favors long holders when rates fall and short holders when rates rise.
Convexity Adjustment ≈ 0.5 × σ² × T_1 × T_2 (Where Futures Rate = Forward Rate - Convexity Adjustment)
Cole Barrett's Reality Check
The Unvarnished Bottom Line"Futures settle daily in cash; forward agreements settle once at maturity. That daily cash flow creates convexity bias. If you are long interest rate futures and rates drop, your broker deposits cash into your account immediately, which you can reinvest at prevailing rates. Because of this cash-flow timing edge, interest rate futures trade at a persistent premium to OTC forward contracts."
Interactive Simulator: Test the Math
Real-World Example: Scenario Breakdown
Examining the real numbers for: Hedging a $10,000,000 3-year interest rate liability using CME SOFR futures vs. an OTC Forward Rate Agreement (FRA)
| Execution Metric | Convexity-Adjusted Institutional Desk | Unadjusted Corporate Treasurer |
|---|---|---|
| Fee / Rate | Standard exchange clearing pass-through | $1.50 ticket fee |
| Spread / Buffer | Applied mathematical convexity adjustment subtracting 12 basis points from futures quote | Treated SOFR futures prices as direct 1-to-1 equivalent to OTC forward rates |
| Execution / Status | Matched true OTC forward cash-flow liability cleanly | Daily margin variance cash flows compounded against the trade |
| Total Cost / Result | Accurate institutional interest rate immunization | Hedge broken by unadjusted futures convexity divergence |
How Brokers Weaponize This Term
Futures brokers promote interest rate futures as exact substitutes for interest rate swaps without disclosing that daily margin variation creates convexity drift that can disrupt long-dated corporate debt hedges.
Broker Evaluation Matrix
Cole Approves
Interactive Brokers: Trader Workstation (TWS) provides direct CME SOFR and Treasury futures trading with built-in convexity analytics and forward-curve calculators.
Read Audit →Cole Flags / Avoids
Retail CFD Desks: Offers synthetic interest rate CFDs that strip out exchange mark-to-market mechanics while charging asymmetrical overnight financing markups.
View Trap Details →Frequently Asked Questions
Why did financial markets transition from Eurodollars to SOFR?
Eurodollar futures were pegged to LIBOR, which was phased out due to manipulation scandals; SOFR (Secured Overnight Financing Rate) is backed by overnight Treasury repo collateral.
How does volatility affect convexity bias?
Higher interest rate volatility expands the convexity adjustment, widening the pricing gap between exchange-traded futures and OTC forward contracts.