Option Stress Testing

For educational purposes only; not investment advice.

Direct answer

An option stress test reprices the entire portfolio under a deliberately adverse, internally consistent scenario. It should combine underlying gaps, changes across the volatility surface, elapsed time, correlation or basis moves, wider spreads, and exercise, assignment, settlement, and margin cash needs. It is a vulnerability test, not a forecast or a probability estimate.

How it works

Start from an executable liquidation value using a documented quote convention and a complete inventory of options, stock, cash, and obligations. Define historical and hypothetical scenarios, then fully reprice every position:

scenario P&L = scenario liquidation value - current liquidation value + scenario cash flows

stress loss = max(-scenario P&L, 0)

Also calculate liquidity separately: cash and borrowing capacity minus margin demands, delivery payments, and settlement obligations. A useful scenario matrix varies price jumps, volatility by expiry, skew twists, 0/1/5 days of decay, correlation and basis, bid-ask width and fill size, rates, dividends, borrow availability, and early exercise or assignment. Greeks are a useful cross-check, but large nonlinear moves generally require full repricing.

Use several severities and record action thresholds before the event: maximum stress loss, minimum remaining buying power, deliverable cash, and concentration or executable-size limits. A reverse stress test instead asks which combination first breaches one of those limits.

Example

Assume a $100,000 account holds several index and single-stock options. An adverse scenario applies an -8% index gap, +15 volatility points to short expiries, +8 points to later expiries, a +6-point downside-skew steepening, one day of decay, weaker diversification, and spreads that double.

Progressive full repricing produces cumulative estimates of -$2,400 after the price move, -$4,900 after the volatility surface, -$5,300 after time and basis effects, and -$6,000 at executable liquidation prices. These rows are stages, not amounts to add. Stress loss is $6,000, leaving estimated equity of $94,000. A separate assignment analysis shows $12,000 of possible delivery cash, which may be the binding constraint even though it is not an additional trading loss.

Risks and limitations

A scenario can omit the path that matters; test jumps, delayed exits, and combined shocks rather than one factor at a time.
Model marks may not be executable when markets are discontinuous or depth disappears.
Margin requirements and assignment timing can change available liquidity before positions can be closed.
Correlations, skew, dividends, rates, and borrow conditions can break from their recent relationships.
Stress results are conditional estimates, not maximum-loss guarantees or probabilities.

Common misconceptions

“Expiration payoff is enough.” Interim volatility, margin, assignment, and liquidity can dominate before expiration.

“Adding independent Greek shocks captures the portfolio.” Large moves include curvature and interactions that linear approximations miss.

“A passed stress test means the trade is safe.” It means only that the chosen scenarios and assumptions stayed within the chosen limits.