This calculator implements the European Black-Scholes-Merton model with a continuous dividend yield. Its price and signed Greeks describe the entered assumptions. Sensitivity charts, matched call/put parity and expiry strategy ledgers help inspect those assumptions; none predicts a future market quote.
What Black-Scholes Actually Says
The European Black-Scholes-Merton model uses constant volatility and continuous interest/dividend yields. It does not model American early exercise or discrete dividend dates. r and q are continuously compounded annual interest and dividend yields; T is days divided by the selected 365-day or 252-day year. σ is annual volatility. Both the underlying and strike are discounted. N(·) is the standard normal CDF; the result is a European theoretical price under the entered assumptions.
European put-call parity with continuous dividends is C − P = S·e^(−qT) − K·e^(−rT). Compare the same strike, expiry, interest rate and dividend yield. A market difference alone does not prove an executable arbitrage.
The Greeks and How Options Move
Greeks describe local changes while other assumptions stay fixed. Positive theta means price increases as time passes; negative theta means it decreases. Deep ITM European puts can have positive theta. These sensitivities do not predict tomorrow’s quote.
Price and Greeks use the selected per-share or per-contract basis; contract values multiply by the entered shares per contract. Theta is signed annual theta divided by 365 or 252. Vega, rho and dividend sensitivity are per 1 percentage point; delta and gamma are per USD spot change and its square, respectively.
Read all six signed Greeks with their units. Vary spot, volatility or time in separate price/Greek panels; inspect a point by chart, row or keyboard. Pin up to two assumption sets for a common-unit comparison. These are isolated sensitivities, not forecasts.
Limitations You Need to Know
The model assumes constant volatility, continuous rates/dividends, frictionless trading and European exercise. It does not price American early exercise, discrete dividends, transaction costs or changing volatility surfaces. A broker may use a different model or quote convention. Market supply, demand and spreads determine executable prices; model differences alone do not establish an arbitrage.
The local implementation uses a normal-CDF series, direct/logarithmic tails and continued fractions to reduce cancellation. Results outside finite representable precision are unavailable rather than fabricated zeroes. The IV solver distinguishes price bounds, expiry, numerical range and nonconvergence, and checks the actual pricing residual. A boundary premium may not identify a unique finite IV.
Saving entered assumptions on this device is opt-in. Share opens a preview with blank values by default; including inputs is an explicit choice and puts that snapshot into the link. Copy, CSV, PDF and Print contain the current assumptions and results. A shared link can be read by its recipient.