What does a cash-secured put calculator estimate?
This calculator estimates a short put’s expiration profit or loss and the gross cash needed to buy the shares if assigned. A cash-secured put pairs a written put with cash set aside for the strike-price purchase obligation. The model uses your inputs; it has no option quotes and does not predict assignment.
Let K be the strike per share, P the premium received per share, Q the total shares covered, X the stock price at expiration, and F total entered fees. The modeled option result is Q × [P − max(K − X, 0)] − F. The expiration breakeven is K − P + F/Q. If the stock finishes at or above the strike, the put payoff is zero and the maximum option profit is Q × P − F. If the stock falls below the strike, losses grow as the stock price falls. At a zero stock price, the modeled result is Q × (P − K) − F. Gross cash to cover assignment is K × Q; this is the strike-price purchase obligation, not the same as maximum loss.
For example, one standard 100-share put with a 50 strike and 2 premium per share has a 48 expiration breakeven before fees. If the stock finishes at 45, the option payoff is a 500 loss offset by 200 premium, for a 300 modeled loss before fees. Gross cash to purchase 100 shares at the strike is 5,000. These are hypothetical arithmetic examples, not market data.
The calculator assumes a single short put position, a constant multiplier, one expiration price, and no closing trade before expiration. It excludes taxes, interest on reserved cash, commissions not entered, early exercise decisions, partial fills, and changes to contract deliverables. Standard contracts commonly represent 100 shares, but adjusted contracts can differ; enter the applicable deliverable multiplier. Assignment can require buying shares at the strike even when their market value is lower, and the stock could fall further. The tool does not determine whether the strategy fits an investor or account.
Source and date: The Options Industry Council cash-secured put guide (accessed 2026-11-03) describes setting aside funds for assignment, premium-limited gain, substantial downside, and breakeven at strike minus premium. This calculator applies a simplified expiration formula and subtracts user-entered fees.
Frequently asked questions
How much cash is reserved?
The model reports strike × shares deliverable. It uses the gross exercise purchase amount and does not subtract the premium or estimate broker-specific collateral rules.
What is the expiration breakeven?
It is the strike minus premium received per share, adjusted upward by entered total fees divided by covered shares.
Is the premium the maximum profit?
For this short put option position at expiration, the premium received is the maximum option gain before fees, reached when the stock finishes at or above the strike. That does not include possible interest on reserved cash or outcomes after expiration.
Will the put be assigned below the strike?
Assignment is not guaranteed by this calculator. It models the expiration payoff if the stock is at each entered price; actual exercise, assignment, and broker procedures can vary.