A recent question in the inbox: “A bond’s yield forecast was 96 basis points below the actual level. Why would that create a 120 RMB price gap per 1,000 RMB face value?”

Behind that question are the three core ideas of bond investing: rates, price, and duration. If you understand those three, you can explain most bond price moves.

One-line conclusion first: rate moves may look small, but duration amplifies them into price swings. Longer maturity and higher duration mean stronger amplification.

1) Bonds are fixed-income, but your return is not always fixed

Many people think bonds are simple: buy, hold to maturity, collect fixed interest. That is only half true.

Bonds do have a coupon. For example, a 1,000 RMB government bond with a 3% coupon pays 30 RMB per year and returns 1,000 RMB at maturity. That cash flow is fixed.

But in reality, most people buy bonds in the secondary market. The price moves, so your true return changes.

Simple examples (ignoring taxes and fees):

  • Buy a 1,000 RMB, 3% coupon bond for 950 RMB: you earn interest plus a 50 RMB discount gain, so your return is above 3%.
  • Buy the same bond for 1,050 RMB: you lose the 50 RMB premium, so your return is below 3%.

This true return is measured by yield to maturity (YTM). Formally, YTM is the discount rate that makes the present value of future cash flows equal the purchase price (basically IRR). In plain terms: interest plus discount or premium determines what you actually earn.

2) Counterintuitive rule: when market rates rise, bond prices fall

Bond prices are driven by market rates, not just bank deposit rates. Think government yields, interbank funding costs, and the overall cost of money.

A simple scenario:

  • If market rates are 3%, a 3% coupon bond trades around 1,000 RMB, and its YTM is around 3%.
  • If market rates jump to 4%, new bonds will offer higher yields. Your old 3% coupon bond becomes less attractive, so you must lower the price to let buyers earn the new market yield.

So the rule is: market rates and bond prices move in opposite directions.

This is why long bonds surge during rate cuts and drop hard during hikes. The cash flows did not change; the market simply re-priced them using a new rate.

3) Why 96 bps can mean a 120 RMB price gap

Here is the key amplifier: duration.

A simple intuition: if rates move by 1%, a bond price moves roughly by duration percent in the opposite direction (more precisely, modified duration).

Key conversions:

  • 1 basis point (bp) = 0.01%
  • 96 bps = 0.96% (0.0096)

Longer bonds often have higher duration, say 12 to 15. If a bond’s duration is 12.5:

Price change ~ duration x rate change ~ 12.5 x 0.96% ~ 12%

So for a 1,000 RMB face value bond, the price move is about:

1,000 x 12% = 120 RMB

That is the core math behind “96 bps can mean 120 RMB.”

Note: this is a first-order approximation. Convexity matters more for larger moves or longer maturities. But for explaining the amplification effect, this is good enough.

4) Common traps for ordinary bond investors

Trap 1: only look at coupon, ignore YTM

Your true return depends on the price you pay. Always check the approximate YTM at your entry price.

Trap 2: assume “bonds are stable” and ignore duration risk

Long bonds can be volatile. Higher duration means higher rate sensitivity. If you may need the money soon or cannot handle drawdowns, do not load up on long duration.

Trap 3: over-focus on rate predictions

Rate forecasting helps, but risk structure matters more. The following are conceptual observations, not advice:

  • When rates rise, shorter duration typically means smaller price impact.
  • When rates fall, longer duration typically has more upside but also more volatility.

5) Use cases / cautions / one-line summary

  • Use case: understand why bonds fall, or choose between long vs. short duration.
  • Caution: the “duration x rate change” formula is approximate. Real pricing also depends on convexity, coupon, term structure, liquidity, and fees.
  • One-line summary: Rates are the barometer; duration is the magnifier.

Disclaimer: This is for personal learning only and is not investment advice. Investing involves risks.