Counterparty Credit Risk For OTC Derivatives

When to Use

Use this skill when trading Over-The-Counter (OTC) derivatives (e.g. Interest Rate Swaps, FX Forwards, Equity Swaps, Credit Default Swaps) with bilateral counterparties. Unlike exchange-traded futures backed by central clearing houses (CCPs), OTC derivatives carry bilateral Counterparty Credit Risk (CCR). This module calculates SA-CCR-grounded Replacement Cost (RC), a simplified PFE add-on with the regulatory over-collateralisation multiplier, Exposure at Default (EAD = 1.4 × (RC + PFE)), a single-period CVA proxy, and enforces ISDA Master Agreement close-out netting and CSA threshold/MTA collateral call triggers.

Formula grounding: BCBS 279, "The standardised approach for measuring counterparty credit risk exposures" (Basel Committee on Banking Supervision, March 2014, rev. April 2014), consolidated into the Basel Framework as CRE52.

When NOT to Use

• Cleared derivatives: trades routed through a CCP replace bilateral counterparty risk with CCP risk — use CCP margin/risk tooling instead.
• Regulatory capital reporting: the PFE add-on here is a simplified notional × supervisory factor sum. It omits duration-based adjusted notionals, supervisory deltas, maturity factors, and hedging-set correlation aggregation (BCBS 279 paras 151-184), so it must not be reported as a regulatory SA-CCR EAD.
• CVA desk pricing: the CVA here is a single-period, undiscounted proxy ((1-R) × EAD × PD), not the time-bucketed discounted-expected-exposure CVA used for pricing or xVA P&L.
• Two-way CSAs with haircuts: collateral is taken at value, one-way (counterparty posts) only.

Prerequisites

• Active OTC contract mark-to-market (MTM) values and notionals.
• ISDA/CSA parameters: threshold (TH), minimum_transfer_amount (MTA), net collateral held ($C$), net independent collateral amount (NICA, default 0), counterparty probability of default ($PD$), and recovery rate ($R$).
• Note the BCBS 279 definition of $C$: it is net collateral held under the para 143 NICA methodology — variation margin plus net independent collateral. Any independent amount must be included in posted_collateral_usd and passed as net_independent_collateral_usd; NICA legitimately appears twice (once inside $C$, once in the RC floor). Passing it only as NICA overstates both RC and PFE.
• A verified, legally enforceable ISDA Master Agreement before applying netting (see references/standards.md).

Workflow

1. Netting Set Grouping: Aggregate all active MTM contract values under the same ISDA Netting Set ID. Only net under a legally enforceable Master Agreement.
2. Replacement Cost (RC) — BCBS 279 para 144, margined netting set:
   • $V = \sum V_{mtm, i}$; $C$ = net collateral held (VM + NICA, para 143 methodology); $NICA$ = net independent collateral.
   • $RC = \max(V - C,\ TH + MTA - NICA,\ 0)$. The $TH + MTA$ term is a floor: a margined netting set always carries at least the uncollateralised band as exposure, even when MTM is deeply negative.
   • Decision point: an unmargined netting set is represented by $TH = MTA = NICA = 0$, which collapses the formula to $\max(V - C, 0)$ (para 136).
3. PFE Add-On & Multiplier:
   • Add-on aggregate: $\text{AddOn} = \sum_i (\text{Notional}_i \times SF_i)$ with $SF$ from the canonical supervisory factor table in the script — call supervisory_factor("EQUITY_SINGLE") rather than typing a literal (SA_CCR_SUPERVISORY_FACTORS, BCBS 279 Table 2 — interest rate 0.5%, FX 4%, equity single-name 32%, equity index 20%, credit single-name 0.38%–6.0% by rating). Per para 184, halve the factor for a basis hedging set and multiply it by five for a volatility hedging set.
   • Multiplier (para 149): $m = \min\left(1,\ 0.05 + 0.95 \cdot e^{(V - C) / (2 \cdot 0.95 \cdot \text{AddOn})}\right)$; $PFE = m \times \text{AddOn}$.
   • Decision point: if $V - C \ge 0$ the multiplier is exactly 1 and can be skipped; it only reduces PFE when the set is over-collateralised.
4. Exposure at Default — BCBS 279 para 128: $EAD = 1.4 \times (RC + PFE)$. The $\alpha = 1.4$ multiplier is mandatory in SA-CCR; omitting it understates EAD by 40%.
5. CVA Proxy: $CVA = (1 - R) \times EAD \times PD$ — single-period, undiscounted; see When NOT to Use before quoting this as a price.
6. Pre-Trade Limit & CSA Collateral Call Audit:
   • Delivery amount $= \max(0,\ V - C - TH)$. A margin call triggers only when the delivery amount is strictly positive and $\ge MTA$ (inclusive boundary). The strict-positivity condition matters because an unmargined set is modelled with $MTA = 0$, where a bare $\ge MTA$ test would fire a $0 call on every out-of-the-money set.
   • Decision point: this engine computes Delivery Amounts only. An over-collateralised set owes the counterparty a CSA Return Amount, which is not calculated here — "no margin call" means "nothing is owed to us", not "no collateral movement is due".
   • If $EAD >$ Max Credit Limit, block the trade or trigger a mandatory collateral top-up.

Full procedure: see references/workflows.md. Standards reference: see references/standards.md. Printable pre-flight checklist: see assets/checklist.md.

Common Pitfalls

• Gross Exposure Without Netting: Calculating credit exposure contract-by-contract without ISDA legal close-out netting, grossly overstating credit exposure.
• Hard-coding supervisory factors from memory: the frequently mis-remembered "equity 6%" is wrong — BCBS 279 Table 2 sets equity single-name at 32%, equity index at 20%, FX at 4%, interest rate at 0.5%. Always source factors from SA_CCR_SUPERVISORY_FACTORS or the primary table.
• Omitting alpha = 1.4: computing EAD as RC + PFE understates regulatory exposure by 40%; SA-CCR mandates EAD = 1.4 × (RC + PFE).
• Dropping the TH + MTA floor in RC: using $\max(0, V - C - TH)$ (a common textbook shortcut) understates a margined set's exposure whenever $V - C$ falls below the threshold band — para 144 floors RC at $TH + MTA - NICA$.
• Ignoring the PFE multiplier for over-collateralised sets: when $V - C < 0$, PFE must be scaled by the para 149 multiplier (floor 5%), otherwise collateralised sets are over-penalised.
• Ignoring Margin Transfer Thresholds (MTA): Failing to factor Minimum Transfer Amount (MTA) into collateral call triggers, leading to un-collateralized micro-exposure drift; the trigger fires only at delivery amount ≥ MTA.
• Firing a zero-dollar margin call: testing delivery_amount >= MTA alone makes 0 >= 0 true, so every out-of-the-money unmargined netting set (modelled as TH = MTA = 0) reports a triggered call for $0. Require a strictly positive delivery amount as well.
• Reading "no margin call" as "no collateral action": this engine computes Delivery Amounts only. An over-collateralised set owes a CSA Return Amount that is not modelled here; leaving it unreturned understates the counterparty's exposure to you and can breach the CSA.
• Passing NICA only as NICA: $C$ is net collateral held including the independent amount. Supplying an independent amount solely via net_independent_collateral_usd, and not inside posted_collateral_usd, leaves $V - C$ un-offset and overstates RC and PFE.
• Static Default Probabilities ($PD$): Using static credit ratings without updating market-implied $PD$ derived from CDS spreads.

Verification

• Instantiate OtcCounterpartyRiskEngine. Register 3 contracts under Netting Set ISDA_BANK_A: equity swap +$500k MTM, $1M notional, SF 32%; FX forward −$200k MTM, $500k notional, SF 4%; rates swap +$100k MTM, $2M notional, SF 0.5%. Post $300k collateral, TH = $100k, MTA = $50k.
  • $V = $400k$; AddOn $= 320k + 20k + 10k = $350k$; $V - C = $100k \ge 0$ so multiplier $= 1$.
  • $RC = \max(100k,\ 150k,\ 0) = $150k$ (TH+MTA floor binds).
  • $EAD = 1.4 \times (150k + 350k) = $700k$.
  • $CVA = 0.60 \times 700k \times 0.02 = $8{,}400$.
  • Delivery amount $= \max(0, 400k - 300k - 100k) = 0 <$ MTA → no margin call.
• Regression check: a netting set with TH = MTA = C = 0 and net MTM −$900k must report is_margin_call_triggered = False and margin_call_amount_usd = 0.0 (not a triggered $0 call).
• Run python -m unittest discover -s skills/counterparty-credit-risk-for-otc-derivatives/scripts.

Related Skills

• counterparty-and-broker-concentration-risk
• broker-account-margin-call-handling