⏱ 1-Minute Summary A cash-secured put (CSP): sell one put and set aside cash for 100 shares. You collect premium and agree to buy the stock at the strike if it falls there by expiration. It is a bullish income strategy: you get paid to set a buy price, and you only buy if the price comes to you.
1. What Is a Cash-Secured Put?
The position has two parts:
- Short 1 put at a chosen strike.
- Cash collateral equal to the cost of 100 shares at that strike (strike × 100).
If the stock stays above the strike at expiration, the put expires worthless and you keep the premium. If the stock falls to or below the strike, you are assigned and buy 100 shares; at an effective cost of strike minus premium.
The chart above shows the Greeks of a cash-secured put as the stock price moves. It assumes you sell one $190 put, with 45 days to expiry and a fixed implied volatility (IV) of 25% as the baseline, and a stock price of $200 at entry.
At a stock price of 200 (when the stock sits above the strike), the net Delta is about +0.22, a mild bullish tilt; the net Gamma is about -0.020; the net Theta is about +0.06 per day; and the net Vega is about -0.18.
At a stock price of 190 (when the stock sits at the strike), the short put is at the money: the net Delta rises to about +0.47, the net Gamma is the most negative at about -0.028, the net Theta is the highest at about +0.08, and the net Vega is the most negative at about -0.22.
At a stock price of 180 (when the stock falls below the strike), the short put is in the money: the net Delta rises further to about +0.74, the net Gamma eases to about -0.024, the net Theta to about +0.05, and the net Vega to about -0.17.
From a low stock price to a high one, the net Delta falls from about +0.74 at 180 to about +0.08 above 210, so the position is the most stock-like when the stock is below the strike (you are about to be assigned); the net Gamma and net Vega are the most negative near the strike; and the net Theta is the most positive near the strike. This is the slow, positive-theta profile of a cash-secured put: you collect premium while the stock stays above the strike.
2. The Payoff Profile
| Scenario | What happens | Result |
|---|---|---|
| Stock stays above strike | Put expires worthless | Keep premium (max profit) |
| Stock at/below strike | Assigned; you buy 100 shares | Own stock at cost = strike − premium |
| Stock falls far | You still buy at strike | Loss = (strike − stock price) − premium |
The chart above shows the full cash-secured put payoff at expiration; the next two charts repeat the same curve, each focusing on one scenario. It assumes you sell the $190 put for about $2, 45 days out at 25% IV. Scenario 1 is the stock staying above the $190 strike: the put expires worthless and you keep the full $2 premium. Above the strike the line is flat at the maximum profit of about $2.
The chart above repeats the same payoff; here the focus is on the stock at or below the $190 strike. It assumes the same setup: a $190 put sold for about $2, 45 days out at 25% IV. At or below $190 you are assigned the stock at $190: the line starts to fall one-for-one, and the breakeven is about $188. From $190 down to the breakeven the position is still profitable; below it the put loses 1 for every 1 the stock falls.
The chart above repeats the payoff once more; here the focus is on the stock falling far below the strike. It assumes the same setup: a $190 put sold for about $2. On the far left the line falls steeply with the stock, with only the $2 premium as a cushion: at $180 the position loses about $8 ($10 below the strike minus the $2 collected), and at $170 about $18. The maximum loss is the strike minus the premium, if the stock went to zero.
The maximum profit is the premium: it happens when the stock never touches the strike. The risk is the stock falling well below the strike, with the premium as a cushion.
The chart above shows the complete cash-secured put P&L at expiration in one line. It assumes you sell one $190 put for about $2, 45 days to expiration at 25% IV. Above the strike the line is flat at the maximum profit of about $2; at and below the strike it falls one-for-one, with a breakeven near $188. The trade profits as long as the stock holds above the strike and loses only if it falls below the premium-adjusted level, so it is a bet that the stock will not fall far.
The dashed line shows the same short put ten days later, with 35 days left. The whole line sits below the at-expiry line and the breakeven moves much higher — from about $188 at expiry to about $198 ten days in. Ten days in, even with the stock back at the strike ($190) the position is still at a small loss (about -$2.8), because the short put still holds time value you would have to pay to close; it only turns green above roughly $198. As expiration approaches, the dashed line settles up onto the solid one, and the full premium shows up only if the stock is still above the strike at expiry.
The chart above shows how the same 10-days-in curve shifts if implied volatility (IV) moves 10 points from the 25% baseline. The gray solid line is the baseline, the red dashed line is with IV 10 points higher (35%), and the blue dashed line is with IV 10 points lower (15%). Because the cash-secured put is short the put, higher IV raises the cost to buy the put back and pushes the curve down: at the $190 strike the position is about -$4.8 instead of -$2.8, and at $200 about -$1.1 instead of +$0.5; the breakeven moves from about $198 to about $205. Lower IV makes the short put cheaper to close and lifts the curve: at $190 it is about -$0.8, with the breakeven near $192. The premium you collected is fixed, but the cost to exit rises with IV, which is the short-vega side of selling the put.
3. Choosing the Strike and Expiry
- Strike: choose a price at which you would genuinely want to own the stock. Selling a put at a low strike is conservative; a higher (closer to ATM) strike pays more premium but increases assignment risk.
- Expiry: 30–45 days is the common time range: enough time value to be worth selling, not so long that the position is exposed.
The chart above shows how an option's time value decays as expiration approaches. It assumes a stock price of 200 and a fixed implied volatility (IV) of 25% as the baseline; referring to the put chart, the at-the-money line uses a strike of 200, the in-the-money line a strike near 210, and the out-of-the-money line a strike near 190. The at-the-money line (blue) holds the most time value: about $13 with 180 days to expiry, $6.5 at 45 days, and $2 in the final week. The out-of-the-money (red) and in-the-money (green) lines hold less: about $8.5 at 180 days, with the out-of-the-money line falling to about $0.5 in the final two weeks. All three decay to zero at expiry, with the fastest decline in the final weeks for the at-the-money line. This is the premium the cash-secured put seller collects: a 30-to-45-day put still carries meaningful time value, which is why that expiry range is the common sweet spot.
- Volatility: the higher the implied volatility, the more premium you collect for the same strike. (For quantitative high/low thresholds, see the IV Percentile article.)
4. Managing the Position
- Close at a target: many sellers buy back the put when it reaches ~50% of max profit to bank gains early and avoid the last-day risk.
- Roll out: if the stock falls and you still want the position, roll the put to a later expiry (and possibly a lower strike) to collect more premium.
- Assignment: if assigned, you own 100 shares at strike minus premium. You can then hold, sell, or run a covered call, the natural next step into the wheel.
5. When It Works and When It Does Not
- Works well: stocks you want to own at a discount, high-IV environments, range-bound or gently rising markets.
- Works poorly: when you do not actually want the stock (you only wanted premium), or before catalysts where IV is already inflated and the stock can gap through the strike.
⚠️ Platform Data Boundary: This article teaches the cash-secured put mechanics. The platform provides T-1 EOD closing data for backtesting CSPs at daily frequency over multi-day-to-multi-month horizons. Assignment and settlement are modeled from closing prices, not intraday moves.
⚠️ Research Use Only: This article is educational. Selling puts carries real assignment and downside risk; you can lose more than the premium if the stock falls sharply. Nothing here is a buy or sell signal. Use this platform's backtests as historical statistical reference only.