Fundamentals of Credit Risk and Fixed Income Instruments

Lending money always comes with a promise—and the risk that the promise might be broken. In this chapter we explore what can go wrong when a borrower can’t pay, and we map out the main tools people use to invest in debt and manage that risk. By the end, you’ll understand the basic language and building blocks of the credit world.

The Big Picture#

Every loan, bond, or IOU rests on a simple idea: one party lends money to another, with the expectation of being repaid, usually with interest. Credit risk is the uncertainty about whether you’ll actually get your money back. This chapter answers the question “What is credit risk, and where does it show up?” We’ll define default and the loss a lender faces, walk through the main parts of the debt market, and introduce the instruments that give investors exposure to credit risk—from plain vanilla bonds to structured products that slice and share that risk in clever ways. Understanding these fundamentals is the first step toward making smart decisions about lending, borrowing, and investing.

What is Credit Risk?#

When you lend your friend $20 for lunch, you trust they will hand it back tomorrow. That trust is not absolute—there is always a chance, no matter how small, that they forget, run out of money, or decide not to pay. In finance, we call that chance credit risk.

Formally,

Credit risk: The possibility that a borrower fails to meet its payment obligations, causing a financial loss for the lender.

Two things matter: how likely the borrower is to stop paying, and how much you stand to lose if they do. These two go hand in hand.

Default: the moment the promise breaks#

A default is any failure to make a scheduled payment on time. If a company misses an interest payment on its bond, or a homeowner stops paying the mortgage, that is a default. Default does not always mean total loss—sometimes you get part of your money back later—but it is the event that triggers the stress.

Default: The event when a borrower fails to pay interest or principal as promised.

Defaults can be technical (a missed deadline, later fixed) or outright (a bankruptcy filing). For our purposes, we think of default as “the borrower can’t pay what they owe, on time and in full.”

Loss Given Default: how much of your money disappears#

Even after a default, you might recover some value. If you lent 40 from their assets, your loss is $60. That loss fraction is called the Loss Given Default (LGD).

Loss Given Default (LGD): The share of the exposure that is lost if a default occurs, after any recovery.

We often talk about the recovery rate—the percentage you get back. LGD equals 1 minus the recovery rate. So if you recover 40%, your LGD is 60%.

Putting them together: Expected Loss#

A simple but powerful equation sits at the heart of credit analysis:

• Exposure at Default (EAD) is the amount you have at risk when default happens—the amount still owed, or the bond’s face value.
• Probability of Default (PD) is our best guess of how likely default is over a given time horizon.
• LGD tells you how much of that exposure you actually lose.

Think of it like driving a car. The chance of an accident is like PD. The severity of the accident given it happens (how damaged your car gets) is like LGD. And the value of the car is your exposure. Multiplying them gives the expected damage you should budget for.

📝 Section Recap: Credit risk is the risk of loss from a borrower not paying. It breaks down into the probability of default, the loss given default, and the exposure at default. That three-part view is the foundation for all credit analysis.

The World of Fixed Income: A Quick Tour#

Not all borrowers are alike, and debt markets reflect that. We can sort them into broad sectors, each with its own credit risk profile.

Government bonds are issued by national governments. For countries with their own central bank and a strong tax base, these bonds are often treated as “risk‑free” in the sense that the government can always print money to pay its debts. US Treasuries, UK Gilts, and German Bunds fall into this group. Nevertheless, governments can and do default when they borrow in a foreign currency or when their own currency collapses, so even sovereign debt carries some credit risk.

Sovereign bonds are really just government bonds when we talk about the national level, but the label “sovereign” reminds us that each government is its own master—there is no higher court to force repayment. For emerging economies, credit risk can be large, and investors demand higher interest rates to compensate.

Agency bonds sit between governments and pure corporates. They are issued by entities created or sponsored by a government to support specific sectors, like housing or agriculture. They don’t carry the full explicit guarantee of the government, but markets often assume strong implicit backing. Their credit risk is usually low, but not zero.

Corporate bonds are issued by companies. Here credit risk ranges from investment‑grade giants (think large, stable firms) down to high‑yield “junk” bonds of companies with shaky finances. The interest rate a corporation must pay is directly tied to its perceived creditworthiness.

Fixed income: Any security that promises a fixed stream of payments. Bonds are the classic example, but loans and other instruments fit the description as well.

The big picture is this:

Every fixed income instrument, no matter how fancy, ultimately rests on someone’s promise to pay. The credit risk of that promise is what we are here to understand.

📝 Section Recap: Fixed income markets span governments, agencies, and corporations, each with a distinct credit risk fingerprint. The safer the borrower, the lower the interest rate investors demand.

Key Credit Instruments: Bonds, Loans, and Swaps#

Now that we have a map of borrowers, let’s look at the tools investors use to take on credit risk—or to protect against it.

Corporate bonds: a public promise#

A bond is a tradable IOU. When a company wants to borrow, it can issue bonds to the public. Each bond has a face value (the amount to be repaid at maturity), a coupon (the interest paid periodically), and a maturity date. An investor who buys the bond is lending money to the company and becomes a creditor.

Because bonds trade in markets, their prices change daily with news about the company, the economy, and interest rates. A bond’s yield—the annual return you earn if you hold it to maturity—contains a credit spread on top of the risk‑free rate, paying you for taking that credit risk.

Credit spread: The extra yield over a government bond of similar maturity that investors demand for bearing credit risk.

If the company’s health gets worse, its bonds fall in price and the credit spread widens. That is the market repricing the credit risk.

Bank loans: a private debt#

Companies also borrow directly from banks through syndicated loans. A group of banks shares the loan, which is often floating‑rate (tied to a benchmark like SOFR) and secured by the company’s assets. Loans are typically senior to bonds in the capital structure—if the company goes under, loan holders get paid before bondholders. That makes them less risky than bonds from the same issuer. However, loans are less liquid; they don’t trade on exchanges as readily as bonds.

Credit default swaps: insurance against default#

A credit default swap (CDS) is a contract that separates credit risk from the underlying debt. Think of it as insurance on a bond or loan. One party, the protection buyer, pays a periodic fee (the CDS spread) to another party, the protection seller. If the reference entity (the company or sovereign) defaults, the protection seller compensates the buyer for the loss.

Credit default swap (CDS): A derivative contract in which the seller agrees to cover the buyer’s loss if a specified borrower defaults, in exchange for a recurring premium.

You don’t need to own the underlying bond to buy CDS protection. That means CDS can be used to hedge credit risk you already hold, or to speculate on a company’s creditworthiness without owning its bonds. The CDS spread is a pure, market‑traded price of credit risk, watched closely by investors as a real‑time health gauge.

These three instruments—bonds, loans, and CDS—form the core toolkit for credit investors. Bonds give broad, tradable exposure. Loans offer seniority and floating rates. CDS provide a flexible way to trade or hedge credit risk directly.

📝 Section Recap: Corporate bonds, bank loans, and credit default swaps are the main ways to get paid for taking credit risk—or to buy insurance against it. Each offers a different blend of liquidity, seniority, and flexibility.

An Introduction to Structured Credit#

So far we’ve dealt with single borrowers. But what if we pool many loans together and then divvy up the cash flows into different slices, each with its own risk level? That is the idea behind structured credit.

Why structure credit?#

Imagine a bank has made thousands of home mortgages. Individually, each mortgage is small, risky, and hard to sell. But if the bank bundles them into a pool, the overall cash flow becomes more predictable—some people will default, but most will keep paying. Investors can then buy a piece of that pool. That is a securitisation.

The magic—and the danger—lies in how the cash flows are split. The pool issues notes in layers, called tranches (French for “slices”). The most senior tranche gets paid first and takes losses last; it is the safest. The junior or equity tranche gets paid last and takes the first losses; it is the riskiest but offers the highest return. In the middle are mezzanine tranches with intermediate risk.

Tranche: A slice of a structured product that has a defined priority of payment and a specific risk profile.

Two classic structures: CDOs and CLOs#

A Collateralised Debt Obligation (CDO) is a securitisation backed by a pool of debt instruments—often bonds, loans, or already‑securitised assets. The CDO issues its own notes to investors, using the cash from the underlying debt to pay them back, following a set order of who gets paid first (often called a waterfall).

Collateralised Debt Obligation (CDO): A structured product that pools a portfolio of bonds or loans and issues tranches with different risk and return characteristics.

A Collateralised Loan Obligation (CLO) is a CDO where the underlying assets are specifically corporate loans, typically leveraged loans. CLOs are a huge part of the corporate lending world. They allow institutional investors to gain diversified exposure to loan credit risk without managing individual loans themselves.

Why would anyone buy the risky junior tranche? Because if defaults stay low, that slice captures the excess spread—the difference between the interest earned on the loan pool and the interest paid to the safer tranches. It can generate equity‑like returns.

Structured credit: The process of repackaging pools of loans or bonds into layered tranches that redistribute credit risk among investors with different appetites.

Structured products made headlines during the 2008 financial crisis because the risks in mortgage‑backed CDOs were misunderstood. That’s a story for later, but the lesson is simple: slicing risk does not make risk disappear—it just moves it around. The underlying credit risk is the same pool of borrowers; the only thing that changes is who bears how much of it.

📝 Section Recap: Structured products like CDOs and CLOs pool many loans and carve the cash flows into risk‑layered tranches. They let investors fine‑tune their credit risk exposure, but the fundamental driver remains the credit quality of the underlying borrowers.

Summary#

We began with a simple truth: lending money always involves the risk that the borrower won’t pay. That risk—credit risk—has two key pieces: how likely a default is, and how much you lose if it happens. From there we explored the world of fixed income, where governments, agencies, and companies borrow money through bonds and loans, each with its own credit risk profile. We then met the main instruments investors use: corporate bonds that trade on markets, bank loans that sit on balance sheets, and credit default swaps that let you buy or sell credit protection like an insurance policy. Finally, we stepped into the structured credit toolbox, where pools of loans are sliced into tranches, offering a customised menu of risk and reward. The principles stay the same; only the packaging changes.