What is the forward rate bias and how does the carry trade exploit it?

Question

AcadiFi · Accepted Answer

The forward rate bias is the empirical observation that forward exchange rates are biased predictors of future spot rates. UIP says forward = expected spot, but forwards systematically over-predict depreciation of high-yielding currencies. This bias creates the carry trade.

Mechanics: borrow in low-yield currency (funder), convert spot to high-yield currency (target), invest at high rate, convert back at future spot. If the target currency depreciates less than the interest differential, the trade profits. Classic example: borrow JPY at 0.3%, invest in AUD at 4.2%, earn 3.9% if AUD/JPY is unchanged; empirically AUD/JPY actually appreciates slightly on average, boosting returns to 5-6%.

Quadrantine Macro runs a systematic G10 carry portfolio: long top three highest-yielders, short bottom three lowest-yielders, weighted by interest differential. Over 1990-2024, Sharpe ratio around 0.6 but with 30%+ drawdowns in 2008 and March 2020.

```mermaid
flowchart LR
  Funder[Low Yield Currency] --> Borrow[Borrow 0.3%]
  Borrow --> Convert[Spot Conversion]
  Convert --> Invest[Invest at 4.2%]
  Invest --> Unwind[Convert Back]
  Unwind --> PnL{Depreciation > Diff?}
  PnL -->|No| Profit[Carry Profit]
  PnL -->|Yes| Loss[Drawdown]
```

What is the forward rate bias and how does the carry trade exploit it?

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