Each calculator runs entirely in the browser on numbers the reader types in: no login, no account, no market data feed. The prose around every widget explains the formula, walks a worked example, and names the assumptions, because a number whose model is hidden is a number that cannot be judged. Deeper treatments of each concept live in the Learn library.
Free expected move calculator: stock price, implied volatility, and days ahead produce the one and two standard deviation price ranges the options market is pricing.
Free probability calculator for options: the log-normal model probability that a stock finishes above or below a chosen level, the same family of arithmetic behind POP displays.
Free single-leg options profit calculator: strike, premium, and a price at expiration produce the profit or loss, breakeven, maximum profit, and maximum loss for long or short calls and puts.
Free position size calculator for defined-risk options trades: account equity, a per-trade risk budget, and the maximum loss per contract produce the contract count that fits the budget.