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 credit spread calculator for bull put and bear call spreads: max profit, max loss, breakeven, return on risk, credit-to-width and model probability of profit.
Free debit spread calculator for call debit and put debit spreads: max profit, max loss, breakeven, reward to risk and model probability of profit at expiration.
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 options profit calculator for calls, puts and spreads: see profit or loss at any price and date, breakevens, max loss and the chance of profit in plain English.
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.