A bond, stripped to one line: a promise to lend money and collect interest in return. The moment you buy the IOU issued by a government or company, you become a creditor, not an owner (shareholder). You get your principal back at maturity and pocket interest at fixed intervals along the way. The scale of it is a little surprising. The bond market dwarfs the stock market. Global bonds outstanding run well past 100 trillion dollars, larger than total equity market value. The reason is simple: governments and companies must borrow constantly to keep running. At the center of it all sits the U.S. 10-year Treasury yield, the world's de facto risk-free benchmark rate, and that single number is the starting point for almost every asset price, from mortgages to emerging-market exchange rates. Below we take apart the 12 core components of bonds, one at a time.

The skeleton: principal and interest

What a bond is

A bond is an IOU stating that the issuer will repay the principal at maturity and pay set interest until then. If a stock buys you a share of a company, a bond lends money to it. So even if the company collapses, bondholders rank ahead of shareholders in getting paid. Here is the part that trips people up most: bond prices and market rates move like a seesaw, in exactly opposite directions. When market rates rise, already-issued low-coupon bonds lose appeal and their prices fall; when rates drop, prices rise. "Bonds are always safe"? That belief is dangerous. There is real default risk if the issuer breaks its promise, and that risk grows as the credit rating falls. Still, in practice bonds are lower-volatility than stocks and get used to balance portfolios or to earn steady interest income.

Par value: the amount promised at maturity

Par value is the principal promised back at maturity, the face amount printed on the bond. The market trading price swings above (premium) or below (discount) par depending on prevailing rates and the issuer's credit. But the key point is elsewhere: no matter how wildly the trading price swings, if you hold to maturity you get exactly the promised par value back. So a bond bought below par has a built-in extra gain at maturity, while one bought above par has a built-in loss baked in. Par value is also the basis for coupon interest: a 3% coupon pays 3% of par every year regardless of the market price. For example, buy a bond with par of 1,000,000 KRW at 950,000 KRW in the market, and at maturity you receive 1,000,000 KRW, adding a 50,000 KRW gain.

Coupon: interest fixed at issuance

The name "coupon" comes from the detachable interest tickets once attached to paper bonds. Once it is set at issuance, it never changes until maturity. The interest amount you receive is fixed, but when market rates swing, the bond's appeal shifts. When market rates climb above the coupon, people prefer newly issued bonds, so older bonds must be marked down to sell. And here is a common myth: "if rates rise, my coupon rises too, right?" No. The coupon stays put; instead the bond's price falls so its overall yield adjusts. If you hold a 3% coupon bond and new bonds come out at 5%, your bond trades below par so its effective yield matches the market. Distinguishing the stated rate (coupon) from the actual yield (YTM) is the starting point for understanding bonds.

The price-yield seesaw

Yield: it moves opposite to price

Yield expresses how much you earned relative to the principal invested; for bonds it usually means the return from interest. The thing beginners stumble over most is right here: bond price and yield move in opposite directions. For a bond paying the same coupon, a cheaper price means more interest per dollar spent, so yield rises; a pricier bond means yield falls. "Higher yield is always better, right?" That one is risky too. An unusually high bond yield can be a signal that the market sees a lot of default risk. The table below shows how yield moves inversely as the market price changes on a bond with par of 1,000,000 KRW and a 3% coupon (30,000 KRW/year).

Who issues them: Treasuries and corporates

Treasury: the risk-free benchmark

Treasuries are bonds issued directly by a government. Because principal and interest arrive like clockwork unless the nation defaults, they are classified as the safest asset class. So the Treasury yield acts as the starting point for all other asset prices, the so-called risk-free rate. Expected returns on riskier assets are typically priced as this Treasury yield plus extra compensation for risk. That said, "Treasuries never lose money" is flat wrong. Hold to maturity and you get the promised principal and interest, but if market rates rise in the meantime, the market price of a Treasury you hold falls. And governments have defaulted on bonds denominated in foreign currency rather than their own. Treasuries are the classic safe haven that money rushes into when risk aversion spikes, and the reference point for the world's rate structure.

Corporate bond: the credit spread over Treasuries

Corporate bonds are issued by companies to fund their business, the counterpart to government Treasuries. Companies carry more default risk than nations. So to attract investors, they usually have to add higher interest than Treasuries. That "extra interest over Treasuries" is called the credit spread, and it widens as the company's credit rating falls. Treating all corporate bonds as safe is a mistake. If a company struggles, interest can be delayed or principal lost, so risk varies sharply by rating. When the economy weakens, default fears widen spreads and push corporate prices down, which is why the corporate spread also serves as a gauge of market risk sentiment. For the same maturity, a high-quality company's corporate yield often sits 1 to 2 percentage points above the Treasury yield.

Grades of risk: ratings, junk, and default

Credit rating: a report card for repayment

A credit rating compresses, into letters, the likelihood that a company or country will repay borrowed money as promised. AAA is the top, and default risk grows as you move down. BBB (or Baa) and above is usually "investment grade," below it is "speculative grade." Ratings translate directly into the borrower's interest cost. A low rating means lenders demand higher interest; a high rating funds the same money more cheaply. But take a rating as "a guarantee against failure" and you have misread it. A rating is only a relative probability judgment at the time of assessment, not a fixed forecast, and once-top-rated companies have been sharply downgraded. Moody's, S&P, and Fitch assign these grades, and bond investors and institutions use them as the basic yardstick for risk. South Korea's sovereign rating sits around AA, a very stable zone.

Junk bond: high interest tied to high risk

Junk bonds carry ratings of BB or below, so default odds are high, and in exchange they promise high interest for taking that risk. They earned the harsh "junk" nickname but go by the more polite name "high-yield bonds" in the market. Why do they exist? Because low-credit companies and nations still need to borrow, which means offering bigger interest to investors willing to bear the risk. "High interest is always good" is a dangerous delusion. High interest is merely the price of risk, riding alongside a matching probability of loss. Even an 8% coupon means nothing if the issuer defaults before maturity and you lose the principal itself. Yields around 7 to 10% are commonly cited in the junk market, but default rates tend to spike when the economy sours, so this market's spread is often cited as a signal of economic anxiety.

Default: the broken promise

Default is the state of failing to pay a bond's interest or principal on the promised date. It resembles a personal delinquency, but at the company or country scale the fallout is on another level. Once default hits, the credit rating plunges and the cost of future borrowing soars, or market funding shuts off entirely. When a nation falls into default, it often spreads into exchange-rate turmoil, currency shortages, and financial-system shock. The idea that default means "the company vanishes instantly" is also a misconception. In reality, it often runs through negotiations like debt restructuring or partial deferral, so its forms vary. A "technical default" missing a payment date by a few days carries different weight than an outright abandonment of repayment. Sri Lanka declared a de facto sovereign default in 2022 and entered IMF bailout talks. Rating agencies and bond investors price default odds into spreads and ratings in advance.

Signals the market reads: the yield curve and duration

Yield curve: the fortune-teller's light and shadow

The yield curve plots the yields of Treasuries of different maturities in a single line from short to long. Normally it slopes upward, since lending money longer demands more interest. But occasionally short rates exceed long rates in an "inversion." Inversion is read as a signal that the market expects the economy to cool and rates to fall in the near future. Case in point: the U.S. 10-year minus 2-year Treasury spread was inverted from July 2022 to November 2023, about 16 months, the longest on record. And yet it did not lead straight to a recession. By the autumn of 2025 it had normalized to around +0.5 percentage point, with the 10-year near 4.0% and the 2-year near 3.5%. Curve inversion preceded 7 of the past 8 recessions (about 87.5%), earning it the "recession fortune-teller" label, but it can miss or run with a long lag, as in 2019 and this cycle.

✍️ Operator's note — Honestly, treating curve inversion like an ironclad "recession is definitely coming this time" rule is a bit reckless. An 87.5% hit rate is impressive, sure, but the 16-month inversion of 2022-2023 brought no recession, and by autumn 2025 the curve had calmly normalized. Hitting 7 out of 8 doesn't guarantee the 8th, and even when it hits, the lag is so uneven that it's hard to use as a timing tool. Don't go all-in on one signal; read it alongside several indicators.

Duration: how much it sways with rates

Duration is a measure, expressed in years, of how sensitively a bond's price reacts to rate changes. It is often introduced as "the average time to get your invested money back," but its more important practical meaning lies elsewhere: for each 1 percentage point move in rates, the bond's price changes by roughly the duration in percent. So the longer the duration, the more violently the price swings for the same rate move. The belief that "bonds are safe so their price doesn't change" is the dangerous one. The longer the maturity, the more a small rate move whips around the mark-to-market gain or loss. In asset management, when rate rises are expected, managers shift toward shorter-duration bonds to cut risk; when rate drops are expected, they lean into longer-duration bonds to amplify price gains. The table below shows the approximate price drop by duration when rates rise 1 percentage point.

✍️ Operator's note — Plenty of people lately bought long-duration bond ETFs trusting only the line "bonds are safe assets," then took 10%-plus hits when rates rose. If you don't grasp that longer duration means a bigger price swing per notch of rate move, you can't judge whether something is actually safe. One glance at the table makes it obvious that a 7-year and a 2-year are in different weight classes.

Bonds that even fend off inflation

TIPS: defending against inflation through principal

Inflation-linked bonds (TIPS) are Treasuries designed so the principal grows along with rising prices. Ordinary Treasuries return a fixed principal at maturity. So if prices climb a lot in the meantime, the real purchasing power of the money returned gets eroded. TIPS adjust the principal in line with the consumer price index (CPI), guarding against this inflation risk. The stated rate is often set lower than a same-maturity ordinary Treasury, but this is no loss: the inflation compensation is paid separately through principal adjustment rather than interest. So investors focus on the real yield, stripped of inflation, rather than the nominal rate itself. TIPS are frequently mentioned as a diversification tool for preserving an asset's real value when inflation is a concern. For example, if prices rise 3% in a year, the TIPS principal is adjusted up by roughly 3%, and interest then accrues on that enlarged principal.

Cautions and limits

• Bonds are merely lower-volatility than stocks, not risk-free. Rising rates create mark-to-market losses on bonds you hold, and an issuer default can wipe out principal.
• An unusually high yield can be a signal that the market sees a lot of risk. High interest is not free; it is the price of risk.
• Curve inversion has had a high historical hit rate, but lags and exceptions make it a poor single-signal tool for timing a recession.
• A credit rating is only a relative judgment at a point in time and does not guarantee the future; sharp downgrades can happen.
• Longer-duration bonds swing more in price with rate moves, so weightings should be adjusted to the rate outlook.

Get a feel for it on PriceGuess

Concepts like the bond price-yield seesaw, credit spreads, and duration only sink in once you wrestle with the numbers directly. Reading alone won't do it. On PriceGuess, try the higher-lower game to build a sense of which way the market moves by guessing whether a rate or price metric goes up or down, and use the daily challenge to keep sharpening your number sense with a fresh price-estimation problem each day. Bonds aren't a subject to memorize; they're a feel for reading which way the seesaw tips.