Skip to content

FRM Exam Part II · The Evolution of Stress Testing Counterparty Exposures

Stress Testing Design and Scenario Selection for Counterparty Exposures

Updated 11 October 2026 · Fact-checked

Designing a counterparty stress test means choosing scenarios, shocking risk factors, and measuring the effect on exposure and loss. You pick historical, hypothetical or reverse scenarios, calibrate severity so they are extreme but plausible, and include wrong-way risk so exposure and default likelihood move together.

Understand Stress Testing Design and Scenario Selection

A stress test asks what happens to your counterparty exposures if markets or counterparties move far beyond normal conditions. VaR-style and PFE measures rely on historical volatility and a chosen confidence level. Stress tests cover the tail those measures can miss.

There are three main scenario types. A historical scenario replays a past episode, such as 2008 or March 2020, by applying the observed risk factor moves to today's portfolio. It is credible and easy to explain, but it only covers what has already happened. A hypothetical scenario is built by judgment. It describes a plausible future event, such as a sharp rate rise with a sovereign downgrade, and sets shocks to each risk factor. It can capture new risks but depends on the designer's imagination.

A reverse stress test works backwards. You start from an unacceptable outcome, such as a loss that breaches capital or a counterparty default that causes a given loss. Then you search for the scenarios that produce it. It shows hidden vulnerabilities and tests whether you are comfortable with how likely those scenarios are.

Severity calibration balances two aims. A scenario must be severe enough to be informative, yet plausible enough that management takes it seriously. Too mild a test gives false comfort. Too extreme a test gets ignored. Good design shocks many risk factors together (rates, FX, credit spreads, equity, commodities, volatility) and keeps their relationships consistent, because correlations rise in a crisis.

Wrong-way risk is when exposure to a counterparty rises as its creditworthiness falls. Examples are a bank buying put protection from a counterparty correlated with the underlying, or a firm trading with a counterparty holding collateral issued by itself. Stress tests should link the counterparty's default probability to the market shock. Ignoring this link understates loss. Also stress collateral values, haircuts, margin period of risk and netting effectiveness, since they change net exposure in a crisis.

Key formulas to remember

Stressed exposure
Stressed exposure = max(Stressed portfolio MtM − Collateral held after haircut, 0)
For a netting set, net the trades first, then subtract collateral. Exposure cannot be negative.
Stressed loss at default
Loss = Stressed exposure × LGD
Use stressed LGD if recoveries or collateral values fall in the scenario.
Stressed expected loss
EL = PD(stressed) × LGD(stressed) × EAD(stressed)
Under wrong-way risk, PD and EAD rise together, so do not treat them as independent.
Collateral after haircut
Collateral value = Market value × (1 − haircut)
Haircuts may widen in stress.
Reverse stress test logic
Fix loss target L*, then find shocks s such that Loss(s) ≥ L*
The outcome is fixed first; the scenario is the output.

How to solve Stress Testing Design and Scenario Selection questions

Use this order for any question on designing or evaluating a counterparty stress test.

  1. 1Identify the purpose: limit setting, capital, or finding vulnerabilities. This shows which scenario type fits.
  2. 2Identify the scenario type: historical, hypothetical or reverse, and note its strengths and limits.
  3. 3List the risk factors the portfolio depends on and shock them together and consistently.
  4. 4Check severity: extreme but plausible, and not just a larger version of VaR.
  5. 5Apply the shocks to revalue trades, net them, then subtract stressed collateral.
  6. 6Add wrong-way risk by linking counterparty PD, LGD or collateral quality to the shock.
  7. 7Compute stressed exposure and loss, and compare with limits or capital.
  8. 8Interpret: state what the result means and what action follows.

Quickest way: Match the question to the scenario type

When to use it: Use this for conceptual MCQs asking which approach or design feature fits a situation.

  1. Past event replayed on today's portfolio means historical.
  2. Judgmental future story means hypothetical.
  3. Start from a loss or failure and find the cause means reverse.
  4. Exposure rising as the counterparty weakens means wrong-way risk.
  5. Scenario too mild or ignored for being implausible points to a severity calibration problem.
  6. For numbers, net first, subtract haircut collateral, floor at zero, then multiply by PD and LGD as asked.

Common mistakes in Stress Testing Design and Scenario Selection

  • Saying a reverse stress test starts with a scenario and measures its loss.

    The name is confused with ordinary scenario testing.

    Fix: Remember it starts with the bad outcome and works back to the scenarios that cause it.

  • Shocking one risk factor at a time.

    It is simpler and mirrors sensitivity analysis.

    Fix: Shock related factors together with consistent correlations, since crises move many factors at once.

  • Treating PD and exposure as independent in stress.

    Standard EL formulas multiply them separately.

    Fix: Under wrong-way risk, raise PD in the same scenario that raises exposure.

  • Assuming historical scenarios are the most severe possible.

    Past crises feel like worst cases.

    Fix: Remember history is limited to observed events; hypothetical and reverse tests cover unseen risks.

  • Forgetting to floor exposure at zero or to apply haircuts to collateral.

    Candidates rush the arithmetic.

    Fix: Net trades, deduct collateral after haircut, then take the maximum with zero.

Worked examples

Example 1

A bank has a netting set with a counterparty. In a stress scenario the net mark-to-market is USD 80 million. Collateral held is USD 50 million of bonds, and the stress haircut on them is 10%. Stressed PD is 20% and stressed LGD is 60%. What is the stressed expected loss?

Show the solution
  1. Collateral after haircut = 50 × (1 − 0.10) = USD 45 million.
  2. Stressed exposure = max(80 − 45, 0) = USD 35 million.
  3. Stressed EL = 0.20 × 0.60 × 35 = 0.12 × 35 = USD 4.2 million.

Answer: USD 4.2 million

Example 2

A risk committee finds its counterparty stress tests all use 2008 moves. It wants to find which combinations of shocks would cause a loss above its capital buffer for a hedge fund counterparty. Which approach fits, and why?

Show the solution
  1. The aim is to start from a loss threshold, the capital buffer breach.
  2. Searching for scenarios that produce a fixed outcome is a reverse stress test.
  3. A historical test only replays 2008, and a hypothetical test begins with a chosen story rather than the loss target.
  4. The result shows hidden vulnerabilities, and the committee can judge whether those scenarios are plausible.

Answer: A reverse stress test, because it starts from the unacceptable loss and identifies the scenarios that cause it.

Exam tips

  • Expect conceptual MCQs that ask you to match a scenario type to its description. Learn the one-line definitions.
  • For numerical questions, always net, deduct haircut collateral, floor at zero, then apply PD and LGD.
  • If a question mentions a counterparty linked to the underlying or collateral, think wrong-way risk.
  • Watch for answer options that say stress tests replace VaR or PFE. They complement them.
  • Severity questions favor extreme but plausible, not the largest conceivable shock.

Practice questions from The Evolution of Stress Testing Counterparty Exposures

Stress Testing Design and Scenario Selection in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Stress Testing Design and Scenario Selection: frequently asked questions

What is the difference between reverse and scenario stress testing?

Scenario stress testing starts with a scenario and measures its impact. Reverse stress testing starts with a defined failure or loss and finds the scenarios that cause it. Reverse tests help uncover vulnerabilities that chosen scenarios miss.

Why is wrong-way risk important in counterparty stress testing?

In stress, exposure to a counterparty can rise just as its default probability rises. If you treat them as independent, you understate expected loss. Stress tests should therefore link them in the same scenario.

How severe should a counterparty stress scenario be?

It should be extreme but plausible. If too mild, it gives false comfort. If too extreme, management may dismiss it and not act on the results.

Are historical scenarios enough for stress testing?

No. They only cover events that have already happened. Hypothetical and reverse scenarios are needed to capture new or unobserved risks.