External and Internal Credit Ratings and Country Risk

A bank's credit committee approves a $200 million loan to a Brazilian utility based on the borrower's BBB+ rating. Six months later the sovereign is downgraded two notches and the loan reprices 250 basis points wider. The borrower's rating did not change, but the country ceiling fell. The credit risk you took was not the one printed on the rating letter.

S&P, Moody's, and Fitch publish ordinal ratings that rank credit risk. Investment grade runs AAA/Aaa down to BBB-/Baa3; below that is speculative grade or high-yield. Agencies use different default designations: S&P and Fitch use D for default, while Moody's C is its lowest grade and is typically associated with default and little recovery prospect. The investment-grade boundary matters because many institutional mandates restrict holdings to those grades.

KEY: An issuer rating ranks creditworthiness rather than supplying a complete loss forecast. Issue ratings may also reflect security, seniority and recovery. Model default probability and loss given default separately under the chosen methodology.

Common mistakes

• Substituting recovery rate for LGD. LGD is 1 − RR. A bond with 40% recovery has 60% LGD, not 40% LGD. Trap: a question gives RR = 40%, EAD = $10M, PD = 2%. The right answer is 2% × 60% × $10M = $120K.
• Assuming constant hazard for high-yield bonds. Default rates for low-grade bonds are not constant. They spike in recessions and decay in expansions. Constant-hazard math gives wrong cumulative defaults for BB and below. Trap: the question describes a high-yield issuer, and a choice based on $\lambda t$ approximation underestimates 5-year cumulative default.
• Confusing TTC and PIT philosophies. TTC ratings should not change in a recession unless the firm's cycle-relative position changes; PIT ratings should. A question that describes a downgrade during a recession and asks whether the model is TTC or PIT is testing this distinction.

Bottom line

• External ratings rank credit risk; investment grade ends at BBB-/Baa3. Issuer and issue ratings have different scopes, and neither replaces calibrated PD and LGD inputs.
• The BBB-/Baa3 boundary drives institutional mandates and creates a price cliff that matters more than any single notch within a category.
• Through-the-cycle (TTC) ratings smooth across the cycle; point-in-time (PIT) ratings reflect current conditions. IFRS 9 ECL uses PIT; Basel capital often uses TTC to avoid procyclicality.
• Hazard rate is the instantaneous default intensity. Cumulative PD over t years equals $1 - e^{-\lambda t}$; conditional one-year PD is $1 - e^{-\lambda}$ under constant λ.

Exam shortcut

When a question gives PD, recovery rate, and exposure, your first step is to convert recovery to LGD: LGD = 1 − RR. Skip the conversion and you walk into the trap distractor every time. For multi-year cumulative default with a constant hazard, use $1 - e^{-\lambda t}$; the linear approximation $\lambda t$ only works when $\lambda t$ is below 5%.

The full lesson (about 5,488 words, 37 min read) adds 2 worked examples, all 6 common mistakes, a self-check, free in the app.

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