Interest Rates & Bond Prices

A bond's price isn't broken just because it moved — it moved because the world around its fixed promise changed.

• Explain why a bond's price moves in the opposite direction to prevailing interest rates, even when nothing about the issuer or the bond's coupon has changed.
• Estimate a bond's approximate price at a given interest rate using the coupon ÷ prevailing yield relationship, and recognize this as a simplified teaching approximation.
• Distinguish between a bond's fixed coupon payment (which never changes) and its market price (which constantly adjusts) to avoid mistaking a rate-driven price drop for a sign of issuer trouble.

A bond's coupon never changes. But its price does — constantly — and the reason is simple: a fixed payout is only worth as much as it compares to what else is available right now.

Think of a bond as a promise: "Pay me ₹1,000, and I'll give you ₹60 every year." When prevailing interest rates are 6%, that promise is priced at exactly ₹1,000, because ₹60 ÷ 6% = ₹1,000. The coupon matches what the market currently expects, so the bond trades at "par" — its price equals its face value.

Now the world changes. Interest rates rise to 8%. New bonds start paying ₹80 a year for the same ₹1,000. The old bond hasn't changed at all — same issuer, same ₹60 coupon, same face value of ₹1,000. But nobody will pay ₹1,000 for a ₹60 payout when ₹80 is now available elsewhere. So its price has to drop until that same ₹60 coupon works out to a competitive 8% return: ₹60 ÷ 8% = ₹750.

Nothing about the bond broke — the world around it moved, so the price moved with it.

Nothing about the bond broke. The world around it moved, and the price moved to keep the promise competitive.

This coupon ÷ prevailing yield calculation is a quick way to estimate direction and rough scale — not the bond's exact real-world price. Real pricing also depends on how much time is left until the bond matures, which is why two bonds with the same coupon can react by different amounts to the same rate change. That's a layer for later; for now, the direction matters most: rates up, price down. Rates down, price up.

The takeaway to carry forward is this: a fixed number — a coupon, a rate — is never safe from comparison. It's only ever as good as what it's being measured against.

Take a bond with a face value of ₹1,000 that pays a fixed annual coupon of 6%, or ₹60 a year. When prevailing interest rates are also 6%, this bond is priced at exactly its face value: ₹60 ÷ 6% = ₹1,000. Its fixed payout matches what the market currently expects, so it trades at par.

Now suppose interest rates rise to 8%. New bonds issued today pay ₹80 a year for the same ₹1,000. This older bond still only pays a fixed ₹60 — nothing about it has changed — so nobody will pay ₹1,000 for it anymore. Its price has to fall until that same ₹60 coupon offers a competitive 8% return: ₹60 ÷ 8% = ₹750.

The bond's price fell from ₹1,000 to ₹750 — a 25% drop — purely because interest rates rose by 2 percentage points. The issuer didn't default. The coupon didn't shrink. Nothing about the bond itself changed at all.

This coupon ÷ yield calculation is a simplified, perpetuity-style approximation meant to show the direction and rough scale of the relationship. Real bond pricing also accounts for time-to-maturity, which is why two bonds with the same coupon can react by different amounts to the same rate change — that's a topic for a more advanced unit.

Point: A bond's price is not a fixed feature of the bond — it is a constantly recalculated comparison between the bond's fixed coupon and whatever return new bonds currently offer, which is why price and prevailing rates move in opposite directions.

• Assuming a falling bond price means something is wrong with the bond or the issuer, like a risk of default. — Learners are used to stock prices falling on bad company news, so they carry that same 'price drop = problem' logic over to bonds. Fix: Before worrying, ask: did interest rates move, or did the issuer's actual financial health change? A rate-driven drop says nothing about the issuer's safety.
• Treating a bond as a completely fixed, unchanging investment once bought — expecting its price to stay as stable as a fixed deposit. — The word 'fixed' in 'fixed coupon' or 'fixed income' gets misread as meaning the whole instrument's value is locked, not just its yearly payout. Fix: Remember: only the coupon payment is fixed. The market price keeps adjusting so that fixed payout stays competitive with whatever rates are current.
• Treating the coupon ÷ yield formula as the exact, complete way real bond prices are calculated. — Seeing a clean formula produce a specific number, like ₹750, makes it feel precise and final. Fix: Use it only to judge direction and rough scale. Real pricing also factors in time left to maturity, so treat this as a teaching estimate, not a trading tool.

• A bond's coupon payment is fixed, but its market price is not — the price constantly adjusts to keep that coupon competitive with current interest rates.
• When prevailing rates rise above a bond's coupon rate, the bond's price falls; when rates fall below it, the price rises.
• A bond's price can drop 25% with nothing wrong with the issuer — the drop can come entirely from a change in prevailing interest rates.
• Coupon ÷ prevailing yield gives a rough estimate of price direction and scale — it's a teaching tool, not the exact real-world pricing formula.
• Before reacting to any bond price move, ask 'compared to what, and as of when?' instead of assuming the asset itself has a problem.

Q1. When prevailing interest rates rise above a bond's fixed coupon rate, what typically happens to that bond's market price?

• The price falls, so the fixed coupon still offers a competitive return
• The price rises, to reward existing bondholders
• The price stays exactly the same, since the coupon is fixed
• The bond automatically stops paying its coupon Answer: The price falls, so the fixed coupon still offers a competitive return — A bond's coupon never changes, but its price does. When new bonds offer a better payout because rates rose, an old bond's price has to drop until its fixed coupon works out to a competitive return.

Q2. A bond's price drops sharply right after interest rates rise, even though the issuer's finances are completely unchanged. What is the most likely explanation?

• The bond is now riskier because the issuer may default
• The drop reflects the coupon becoming less competitive against new, higher-paying bonds
• The bond's face value was reduced by the issuer
• The market made a pricing mistake that will soon reverse Answer: The drop reflects the coupon becoming less competitive against new, higher-paying bonds — A price drop after a rate rise doesn't mean the issuer is in trouble. It simply means the bond's fixed coupon is now less attractive compared to what new bonds currently offer, so its price adjusts downward.

Q3. True or False: Once you buy a bond, its market price stays fixed and stable for as long as you hold it, similar to a fixed deposit. Answer: False — Only the coupon payment is fixed. The bond's market price keeps adjusting so that fixed payout stays competitive with whatever interest rates the market currently offers.

Q4. A bond has a face value of ₹1,000 and pays a fixed annual coupon of ₹50. If prevailing interest rates fall to 5%, roughly what would you expect this bond's price to be, using the coupon ÷ prevailing yield estimate? Answer: Approximately ₹1,000 (₹50 ÷ 5% = ₹1,000) — Using the simplified estimate, ₹50 ÷ 5% = ₹1,000. Since the coupon rate now matches the prevailing rate, the bond trades close to its face value — this is the 'par' situation.

Q5. Rates rise from 6% to 10%. Someone holding an old bond with a fixed 6% coupon says: "My bond's coupon is fixed, so its price won't be affected by this at all." Does a fixed coupon protect the bond's price from rate changes? Reveal: Weak: yes, if the coupon itself doesn't change, the price shouldn't either. Strong: as rates climb, the gap between this bond's fixed 6% coupon and what new bonds now offer (10%) grows wider, pushing its price down further to stay competitive — the coupon being fixed is exactly why the price has to move instead.