A single-leg option's profit at expiration is its intrinsic value at the final stock price minus the premium paid, or the premium kept minus intrinsic value for a short position, times one hundred shares per contract. This calculator computes that payoff, the breakeven, and the maximum profit and loss for long and short calls and puts.
At-expiration arithmetic only, before commissions and fees. Early assignment and pre-expiration marks are not modeled.
At expiration an option is worth exactly its intrinsic value: for a call, the stock price minus the strike when that is positive, otherwise zero; for a put, the strike minus the stock price when positive. A long position's profit is intrinsic value minus the premium paid; a short position keeps the premium minus intrinsic value. Each contract covers one hundred shares, so per-share figures scale by one hundred times the contract count.
A long call, $100 strike, $3.50 premium, one contract, stock at $105 at expiration: intrinsic value is $5.00, profit is (5.00 - 3.50) x 100 = $150. The breakeven is $103.50. At $103.50 the trade is flat, and below $100 the full $350 premium is the loss, no matter how far the stock falls.
Before expiration an option trades at intrinsic value plus time value, so a position can show a loss at prices where the expiration payoff is positive, and early assignment can end an American-style short leg ahead of schedule, as covered in assignment mechanics. Spreads combine two of these single-leg payoffs; the credit vs debit article walks the combined shapes.