Put Selling Calculator

Selling a put transfers the obligation to buy 100 shares at the strike price from the option buyer to you, and the premium is the price paid for accepting that obligation. Because the seller is short an option, the payoff is capped on the upside at the premium collected and open on the downside all the way to a stock price of zero, which is why the maximum loss shown here is the break-even multiplied by the share count. Break-even is simply strike minus premium: at that price the shares acquired through assignment cost exactly what the position took in. Return on cash divides premium by the full collateral of strike times 100, which is the amount a cash-secured seller must set aside; return on margin divides the same premium by a broker requirement that is usually near 20 percent of the underlying value, so the two figures can differ by a factor of five on identical trades. Annualising a 30-day return by multiplying by 365 divided by days to expiration is standard practice for comparing contracts of different lengths, but it assumes the same trade can be repeated twelve times a year at the same premium, which fails when volatility falls. Practitioners commonly sell strikes at 5 to 10 percent out of the money, or in the 0.20 to 0.30 delta band, where delta is a rough proxy for the probability of finishing in the money. Premium scales with implied volatility, so elevated readings around earnings inflate income and risk together. American-style equity puts can be assigned early, and dividends, hard borrow conditions, and gap moves through the strike are the situations the static payoff diagram does not capture.

Put contracts on shares are far older than exchange trading, appearing in Amsterdam in the seventeenth century and in London coffee-house dealing, but they were negotiated privately between counterparties with no guarantee of performance. The modern market dates to 26 April 1973, when the Chicago Board Options Exchange opened with standardised, exchange-listed contracts, and to the founding of the Options Clearing Corporation, which stepped between buyer and seller and removed counterparty risk. Fischer Black and Myron Scholes published their pricing paper in the same year, with Robert Merton extending the framework, which gave dealers a common language for quoting the premium a put seller receives. Listed puts themselves were not introduced until 1977, several years after calls, and were initially restricted while regulators studied their market effects. Systematic put writing moved from a trader tactic to a documented strategy when the CBOE published the S&P 500 PutWrite Index, which tracks a fully collateralised program of selling one-month at-the-money index puts and holding Treasury bills against them, with a history reconstructed back to the late 1980s. Brokerages formalised the distinction between cash-secured and uncovered writing through tiered approval levels, restricting naked put selling to accounts with higher equity and experience. The retail expansion of the strategy, including the put-then-covered-call rotation widely known as the wheel, followed the arrival of commission-free trading and weekly expirations in the 2010s.