Convexity is the curve, not the line. Duration tells you how much a rate-sensitive asset moves for a 1% rate change; convexity tells you that the move accelerates one way and decelerates the other. For HK banks and insurers, falling short rates plus a steepening curve is a convexity tailwind; rising rates plus a flattening curve is a headwind. Because the HK dollar is pegged, the rate that matters is set in Washington, not in Central.
Most traders arriving at the Hang Seng bring a US toolkit: the chart patterns, the stop placement, the sector-rotation playbook. The toolkit is not wrong. It is calibrated to the wrong regime. The single biggest reason is structural and rarely stated out loud: the Hong Kong market is dominated by financials, and Hong Kong does not set its own interest rates.
If you do not know which way convexity is pointing, you are trading half the index blind.
What convexity actually is
Start with duration. Duration is the straight-line estimate: a bond with duration 7 falls roughly 7% if rates rise 1%. But the real relationship is a curve, not a line. Convexity is the curvature, the second derivative of price with respect to yield. Positive convexity means the price rises more when rates fall than it drops when rates rise by the same amount. The payoff is asymmetric in your favour.
Equities are not bonds, but rate-sensitive equities inherit the same geometry. A bank's earnings are a spread business: it borrows short and lends long. When the curve steepens, the spread widens and earnings accelerate; the valuation multiple expands at the same time, so the two effects compound. That compounding is the convexity. It is why HK financials do not move in a straight line with rates. They accelerate into the right regime and stall in the wrong one.
Why this is a Hong Kong story, not a US one
Two structural facts make convexity the dominant factor in Hong Kong specifically, in a way it is not in the S&P 500.
First, concentration. Financials are roughly 40% of the HK market against about 13% in the US. A US trader who buys the index is diversified across technology, healthcare, energy, and industrials; the rate factor is one input among many. A trader who buys the Hang Seng is, whether they intend it or not, making a large bet on a single rate-sensitive sector. The diversification that smooths volatility in SPY does not exist here.
Second, the peg. Under the Linked Exchange Rate System the Hong Kong dollar trades in a 7.75–7.85 band against the US dollar, and the HKMA must follow the Fed to defend it. When the Fed holds, the HKMA holds. When the Fed hikes, HK rates rise regardless of whether the local economy wants them to. The rate that drives 40% of the Hang Seng is therefore set by the FOMC, not by anything happening in Hong Kong. This is why a single-stock chart on an HK bank can break every US technical rule: the dominant force is an exogenous macro variable the chart cannot see.
This is the third hidden factor behind the volatility we wrote about in the broader thesis: you are not trading a name, you are trading HK liquidity, China policy, and rate convexity at once. For the macro backdrop to all of this, see the 35-year trendline analysis →
How the tracker is built
The gauge at the top is a composite score in a range from −1 (full headwind) to +1 (full tailwind), recomputed from three free, no-key market series. Each is measured as a three-month change, because convexity is about the direction of travel, not the level.
| Signal | Source | Reads positive when | Weight |
|---|---|---|---|
| Short-rate trajectory | ^IRX (13-week T-bill) | Rates falling (cuts ahead = tailwind) | 0.25 |
| Yield-curve slope | ^TNX − ^IRX (10Y − 3M) | Curve steepening (wider bank margin) | 0.25 |
| HK financials relative strength | ^HSNF / ^HSI | Financials outperforming the index | 0.50 |
The relative-strength term carries half the weight on purpose. The two rate signals are the theory: what convexity should do given where rates are headed. The HK Finance sub-index relative to the Hang Seng is the market's actual verdict, the empirical confirmation that the regime is real and not just implied by the curve. When the theory and the tape agree, the score moves to an extreme. When they disagree, the score sits in the transition band and tells you to wait.
Positive (green): the wind is at your back for long HK financials. Falling rates, steepening curve, financials leading. This is when to lean in. Negative (red): you are fighting convexity. Rising rates, flattening curve, financials lagging. Long financials here is rowing upstream. Transition (amber): theory and tape disagree, or both are flat. Size down and wait for the score to commit.
What to do with it
The tracker is not a buy signal. It is a regime filter, the macro lens you put in front of the individual thesis. A deep-value HK bank trading below book is a different trade in a green regime than in a red one: same fundamentals, opposite convexity. The fundamentals tell you what to own; convexity tells you whether now is when the market will pay you for owning it.
It is most useful at the turns. The regime that hurts the most, a red reading while the index sells off, is also where the next green flip eventually rewards the patient. Negative convexity compresses HK financials into weakness; the flip to positive is what re-rates them. Watching the score cross from red through amber to green is watching that setup arrive in real time.
One caveat worth stating plainly. This is a directional, educational signal built on three liquid series. It does not price credit risk, it does not see a Taiwan escalation, and it does not replace reading the actual filings. It tells you which way the rate wind is blowing for half the index. That is all, and on a market that is 40% financials and pegged to the dollar, that is a lot.
For the company-level work that sits underneath the macro, start with the Hang Seng market thesis →