The market hidden behind simple IOUs
Stocks get attention. Bonds move the financial system. A bond is just an IOU with dates and dollars attached, but trillions of dollars of IOUs determine how governments borrow, how companies finance themselves, how banks manage liquidity, and how investors price risk.
- A bond is a timed promise of known cash flows
- Bond markets are huge, technical, and central to the financial system
- Riskless bond valuation is just NPV
- Discount bonds are the foundation of all fixed-income pricing
Fixed-Income Securities
Bonds move the financial system. Two lessons build the valuation machinery now; duration, convexity, credit risk, and securitization arrive in upcoming lessons.
The bond market system
How an IOU becomes a bond
A bond starts as a promise. One party needs cash today and promises to pay fixed dollars on fixed dates. Another party has cash and accepts that promise. Press Issue bond to see the cash move and the promised schedule appear.
Needs cash today. Promises a schedule of future payments.
Has cash today. Buys the promise and expects the scheduled payments.
The fixed-income sequence
Fixed income is taught as a sequence: map the industry, value the cash flows, then add risk. This lesson covers the first three pieces — the industry overview, valuation basics, and discount bonds — so that coupon bonds, duration, and credit risk have a foundation later.
What is a fixed-income security?
“Fixed” means the contract specifies the promised timing and amount. “Promised” does not mean guaranteed — default risk comes later. Stocks do not have fixed promised cash flows; dividends and resale prices are uncertain. Plain bonds are easier to value first because cash-flow timing is specified.
Uncertain future dividends and an uncertain resale price. No promised schedule.
A promised coupon and principal schedule with fixed dates and amounts.
Pays $50 every year for 3 years, then $1,000 at maturity.
May pay dividends if the board approves.
Treasury bill pays $1,000 at maturity.
Common stock of a growing company.
How the bond market is classified
Classifying the bond market
The bond market is not one market. It is several markets grouped by issuer and structure. Expand a card to see who issues it, what cash flows it promises, who buys it, and where the risk sits.
Treasury Securities
“Government IOUs.”
Federal Agency Securities
“Agency-related borrowing.”
Corporate Securities
“Company IOUs.”
Municipal Securities
“Local-government IOUs.”
Mortgage-Backed Securities
“Claims on a pool of mortgages.”
Derivatives / Structured Credit
“Engineered claims built on debt or credit risk.”
Short-term, 4–52 weeks, sold at discount or par, pays face at maturity.
2, 3, 5, 7, 10-year; pays interest every six months.
20 or 30-year; pays interest every six months.
Separated interest and principal from eligible Treasury notes/bonds/TIPS; each piece is its own zero-coupon security. Bills and FRNs are not stripped.
Tap a category, then tap a bucket to place it. Tap a placed chip to remove it.
Market size and issuance
Before the chart: which category was largest in 2006?
Most people guess Treasuries. The 2006 data tells a different story.
Historical MIT snapshot · 2006 · not current market data.
U.S. Bond Market Debt, 2006, $ billions
In 2006, mortgage-related debt was the largest category in this MIT snapshot.
Largest slice in this snapshot. This matters because mortgage-related debt later became central to the 2007–2008 crisis.
Outstanding debt is the total amount already out there. Issuance is new debt created during the period.
Mortgage-related bonds were 24% of outstanding debt in the 2006 snapshot but 34% of issuance, showing that this area was growing quickly at the time.
Liquidity: huge market, uneven trading
Huge market, uneven liquidity
Bond markets are huge, but trading differs from stocks. Many bonds do not trade on a centralized exchange. A large issuer can have many different bonds outstanding, each with a different maturity, coupon, covenant, or structure. Some bonds trade often while others trade rarely. Treasuries are generally more liquid; structured products such as CDOs can be much less liquid.
| Segment | Typical complexity | Trading frequency | Price transparency | Liquidity risk |
|---|---|---|---|---|
| Treasury bills / notes | Low | High | High | Low |
| Treasury bonds | Low | High | High | Low |
| Investment-grade corporate | Medium | Medium | Medium | Medium |
| Municipal bonds | Medium | Medium | Medium | Medium |
| Mortgage-backed securities | High | Medium | Medium | High |
| Asset-backed securities | High | Low | Low | High |
| CDOs / structured credit | High | Low | Low | High |
When buyers disappear, price discovery becomes harder. A bond can still have promised cash flows but become hard to sell at a fair price.
Issuers, intermediaries, investors
Three jobs power the bond market: borrowing, lending, and helping the market function. Tap a scenario, then tap a role to place it. Some institutions can appear in more than one role.
- Governments
- Corporations
- Commercial Banks
- States
- Municipalities
- SPVs
- Foreign Institutions
- Primary Dealers
- Other Dealers
- Investment Banks
- Credit-rating Agencies
- Credit Enhancers
- Liquidity Enhancers
- Governments
- Pension Funds
- Insurance Companies
- Commercial Banks
- Mutual Funds
- Hedge Funds
- Foreign Institutions
- Individuals
Bond cash-flow anatomy and risk
Bond anatomy: the promised schedule
Once you know the face value, coupon rate, and maturity, the entire promised schedule is determined. Build one below.
A 3-year, 5% coupon bond with $1,000 face value
Year 1 pays $50, Year 2 pays $50, and Year 3 pays $1,050 — the $50 coupon plus the $1,000 principal returned at maturity.
Build a promised cash-flow schedule
| Period | Coupon | Principal | Total |
|---|---|---|---|
| 1 | $50.00 | — | $50.00 |
| 2 | $50.00 | — | $50.00 |
| 3 | $50.00 | $1,000.00 | $1,050.00 |
At 5.0% coupon on $1,000.00 face value, the annual coupon is $50.00. The last payment is larger because principal is returned at maturity.
This is promised cash flow, not risk-adjusted value. Discounting comes next.
Valuation and the risk menu
Is it truly riskless?
Default risk may be very low, but inflation risk and interest-rate risk can still matter. The risk menu below shows the dimensions that affect a bond beyond simple default.
Toggle a risk, watch the bond react
- Inflation → Purchasing power
- Credit → Payment certainty
Discount bonds and zero-coupon valuation
Pure discount bonds
The simplest bond pays once, at maturity. It is the foundation of all fixed-income pricing because every bond can be decomposed into a set of pure discount bonds.
F = $1,000, r = 5%, T = 3 years.
F = $1, P0 = 0.797, T = 5 years.
Discount a single payment back to today
The payment is fixed at $1,000.00, but today it is worth 86% of face.
Higher required return means lower price today. At r = 0 the price equals the face value; at any positive rate the future payment is worth less today.
The price–yield relationship
For a zero-coupon bond the curve is convex and downward-sloping: higher required return means lower price today. Move the slider to slide the point along the curve.
Summary and mastery check
Answer all questions, then check your work. You can retry any time — mastery is based on correctness, not speed.
- 01
Select all that are fixed income.
- 02
A 3-year 5% coupon bond with $1,000 face pays how much at year 3?
- 03
Which risk means the issuer might not make promised payments?
- 04
A zero-coupon bond pays $1,000 in 3 years. Yield 5%. Is the price above or below $1,000?
- 05
What does STRIPS mean conceptually?
So far, we used one rate. Real bond markets have different rates for different maturities. Next, we use those prices to read the yield curve and infer forward rates.
- 1Fixed-income securities are claims on promised cash flows.
- 2Bond categories differ by issuer, structure, and risk.
- 3Coupon bonds pay intermediate coupons plus principal at maturity.
- 4Zero-coupon bonds pay only once at maturity.
- 5Riskless bond valuation begins with NPV.
- 6Higher discount rates reduce today's price.