Every number OptionProfit shows you — P&L, Greeks, probability of profit, breakevens — comes from a specific calculation. This page explains the model, the inputs, and why we made the choices we did.
Black-Scholes is the industry-standard model for pricing options. It takes five inputs — current stock price, strike price, time to expiration, implied volatility, and the risk-free interest rate — and returns the theoretical fair value of a call or put.
It also produces the Greeks directly from the same calculation: Delta, Gamma, Theta, Vega, and Rho all fall out of the Black-Scholes formula as partial derivatives. One model, one set of consistent outputs.
We chose Black-Scholes because it is transparent, well-understood by professional traders, and computationally exact. It is what your broker uses to mark your positions. It is what market makers use to quote premiums. If your numbers should agree with anyone's, it makes sense they agree with the model the entire market is priced on.
Black-Scholes is only as accurate as its inputs. The input that changes the most — and that static calculators almost always get wrong — is implied volatility.
Most free options calculators ask you to type in an IV number yourself. That number is stale the moment you look it up. IV shifts continuously throughout the trading day, spikes into earnings, and collapses after them. A calculator using yesterday's IV for a position you're entering today is giving you materially wrong numbers for your P&L curve, your Greeks, and your probability of profit.
OptionProfit derives implied volatility by back-solving it from the option's actual market premium using the Black-Scholes model — the same price shown on the chain. This keeps IV self-consistent with the premium used in every calculation. When a premium is not yet entered, the calculator falls back to the chain's reported IV, and as a final fallback to the nearest ATM contract's IV or a conservative default if the chain data is stale.
The same applies to the premium itself. We display the mid-price (midpoint of bid and ask) by default, with an option to switch to bid/ask worst-case fill so you can see the realistic cost of entering and exiting.
Black-Scholes requires a risk-free interest rate as one of its inputs. We source this from the current US Treasury yield — the same benchmark the derivatives market uses. It is fetched automatically each session and applied across all calculations, so you are never working with a hardcoded rate that drifts out of date as the Fed moves rates.
Stock quotes, options chain data, bid/ask spreads, and Greeks are sourced from real market data feeds. Options chain prices reflect current market values and are updated approximately every 15 minutes — the standard for non-exchange-direct data. Outside market hours, the most recent available data is used. We do not interpolate or estimate market prices — if the data is not available for a given strike, it is not shown.
OptionProfit calculates probability of profit analytically using the Black-Scholes risk-neutral framework. For each strategy, the calculator identifies every stock-price interval where the position expires profitable, then sums the lognormal probability that the stock closes inside those intervals — using the strategy's own implied volatility. The method handles any strategy shape: a long call, a four-leg iron condor with two separate profit zones, or anything in between.
This is a statistical estimate based on current market conditions, not a prediction. It tells you the mathematical odds implied by current pricing — what actually happens is up to the market.
The math above doesn't care whether a position is one of the 19 named strategies or something you built yourself. The custom strategy builder lets you pick call/put and long/short for 2 to 6 legs directly, and every leg is priced, summed, and analyzed by the exact same Black-Scholes, Greeks, and probability-of-profit engine described on this page — there is no separate or simplified calculation path for custom combinations.
Black-Scholes assumes constant volatility and log-normally distributed returns. In practice, volatility has a surface — IV varies by strike and expiry (the volatility skew) — and markets have fat tails. It also prices options European-style and does not model dividends, so positions on dividend-paying stocks, or short options carrying early-assignment risk, are close approximations rather than exact. For most planning purposes these assumptions hold well enough. For deep out-of-the-money options, short-dated positions into binary events like earnings, or extreme strike distances, treat the outputs as directional estimates rather than precise figures.
OptionProfit is a planning and analysis tool. It is not a broker, it does not execute trades, and nothing here is financial advice.
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