Single-Leg Option Risk: Payoff and Model Sensitivities
Enter one call or put, long or uncovered short, with a premium quoted per share and a fixed 100-share contract multiplier. The payoff uses that premium; theoretical price and Greeks use the separately entered Black-Scholes-Merton assumptions. Those two prices need not match.
Expiration Payoff
A long call has premium-limited loss and unbounded upside. A long put has premium-limited loss and its best payoff occurs when the underlying reaches zero. Short positions reverse these cash flows: an uncovered short call has unbounded loss, while a short put’s loss is bounded by strike less premium, times the share multiplier. These figures exclude fees and obligations that may arise from exercise or assignment.
Call breakeven is strike plus premium; put breakeven is strike minus premium. A put premium above its strike produces no nonnegative breakeven. The displayed maximum profit or loss is floored at zero when no positive profit or loss exists under the entered payoff.
What the Model Assumes
The pricing and Greeks model is European, with constant annual volatility, continuously compounded rate and continuous dividend yield. Days use 365 per year and months use 12. It does not model American early exercise, discrete dividends, spreads, liquidity, fees or changing volatility. Standard 100-share contracts are assumed; adjusted contracts require a different multiplier.
Probability and Expected P/L
Model probability of profit evaluates the risk-neutral log-normal terminal price distribution at the expiration breakeven. It is not a historical win rate or a real-world success probability. Expected P/L is undiscounted risk-neutral expected terminal payoff minus the entered premium, with the sign reversed for a short position. Financing the premium is excluded.
Why VaR Is Not a Maximum Loss
The one-trading-day delta-normal approximation is z × absolute position delta × spot × volatility / √252. The 95% and 99% figures use z values 1.645 and 2.326. This local linear approximation ignores gamma, volatility shocks and jumps. It can exceed a long option’s premium and does not replace the expiration maximum-loss calculation.
Read Greeks in Position Units
Greeks include the position direction and contracts × 100. Delta measures value sensitivity to a one-dollar spot change; gamma measures change in delta. Theta is value change per calendar day with other inputs fixed. Vega and rho are value changes per percentage-point change in annual volatility and rate. They are local derivatives, not guaranteed future P/L.
Compare Scenarios
- Check the premium and contract multiplier against the instrument.
- Change spot, volatility or time separately and compare theoretical value and Greeks.
- Use the payoff tab to inspect expiration outcomes across the displayed price range. The line chart is not a full distribution or a limit on possible prices.
- Evaluate funding, execution and assignment separately before using any result in a trading decision.