Optionsintermediate

Short Put

Q: Writing a put obligates the writer to:

Buy the stock at the strike if assigned. A short put writer must buy the underlying at the strike if the put holder exercises. The premium compensates for accepting that obligation.

Q: Write a put with K =40 forP = 3. The stock falls to S_T =$35. Profit per share is:

-2. Profit= 3 - \max(40 - 35, 0) = 3 - 5 = -2 per share. The premium offset the first 3 of intrinsic value, but not the full5 of loss.

A short put is written by selling a put option. The writer collects premium $P$ upfront and accepts the obligation to buy the underlying at strike $K$ if the holder exercises. Maximum profit equals $P$ , reached when $S_T \geq K$ . Maximum loss equals $K - P$ , reached if the stock falls to zero. Unlike a naked short call, the downside is bounded because share prices cannot go below zero. The view is bullish to neutral, often used to buy stock at a target price while earning income.

Try it yourself

Payoff at expiry

Pick one position and watch its expiry profile across the underlying price S_T. The dashed line is gross payoff; the solid line is profit after premium.

Try this:

Breakeven 55.00Max profit ∞Max loss −A$5Moneyness ITM

Strike KK = 50

Premiumprem = 5

Current spotS = 52

PREMIUM AT SPOT = 52

Intrinsic valueA$2

Time valueA$3

PremiumA$5

Why it matters

Writing a put is getting paid to set a buy limit. The writer is essentially saying "I am happy to own this stock at $K$ if it falls. Pay me $P$ now for that commitment." If the stock stays above $K$ , the writer keeps the premium and never buys anything. If the stock falls, the writer is assigned and ends up long at an effective cost of $K - P$ . The risk is that the assignment happens after a sharp drop, leaving the writer with a paper loss on the stock immediately.

Before you read on — recall

Writing a put obligates the writer to:

Formulas

Profit at expiry

\text{Profit} = P - \max(K - S_T, 0)

Profit

= P

for

S_T \geq K

. Loss grows linearly as

S_T

falls below

K

. Bounded below at

-(K - P)

when

S_T = 0

Break-even at expiry

S_T^* = K - P

Same level as the matching long put break-even, viewed from the writer's side.

Worked examples

Scenario

Write a 1-month put on Wesfarmers with $K =$ $55 at premium $P =$ $1. At expiry $S_T =$ $58.

Solution

Payoff $= -\max(55 - 58, 0) =$ $0. Profit $= 1 - 0 =$ $1 per share. The put expired OTM, the writer keeps the full premium, and no shares change hands. On one ASX contract of 100 shares, that is $100 of income.

Scenario

Same trade, but Wesfarmers falls to $S_T =$ $40 after a profit warning.

Solution

Payoff $= -\max(55 - 40, 0) =$ -$15. Profit $= 1 - 15 =$ -$14 per share. The writer is assigned and ends up long at an effective cost of $K - P =$ $54, against a market price of $40. The loss of $14 per share is real but bounded. The worst case would be the share going to zero, capping the loss at $54 per share.

Common mistakes

✗Short puts have unlimited risk like naked calls. Maximum loss is bounded at $K - P$ because a stock cannot fall below zero. Risk is large but finite.
✗Writing puts is a free way to earn yield. The writer is taking equity risk equivalent to a long stock position with capped upside. In a sustained bear market, repeated short puts can compound losses just like a long-only portfolio.
✗A cash-secured short put is the same as a naked short put. Cash-secured means the cash to honour the strike is set aside, which removes funding risk but does not change the economic loss profile.

Revision bullets

•Sell a put to collect premium $P$
•Max gain $= P$ when $S_T \geq K$
•Max loss $= K - P$ (only if $S_T = 0$ )
•Bullish to neutral view, bounded downside
•Often used as a paid buy limit order

Quick check

Writing a put obligates the writer to:

Write a put with $K =$ $40 for $P =$ $3. The stock falls to $S_T =$ $35. Profit per share is:

Connected topics

Put Long Put Short Straddle Synth. Stock Payoff Shapes

More in Options

Options 101 Call Premium Am. vs Eu.Moneyness Intrinsic Time Value Break-even

In learning paths

Options Path

Sources

Hull (2022), §10.4, §12.1
Hull, John C. Options, Futures, and Other Derivatives. 11th ed. Pearson, 2022. ISBN 978-0-13-693997-9.
Standard textbook treatment of the short put position, profit profile, and the assignment mechanism.
McMillan (2012), Ch. 6
McMillan, Lawrence G. Options as a Strategic Investment. 5th ed. Prentice Hall Press, 2012. ISBN 978-0-7352-0466-2.
Strategy reference on naked and cash-secured short put writing, with explicit profit and loss profile and use as a paid buy limit.
OIC Short Put Strategy
Options Industry Council. Strategy Guide: Cash-Secured Put. Options Education, accessed 2026.
Industry strategy guide explaining the cash-secured short put, profit and loss diagram, and bounded maximum loss.
ASX Clear Margin Rules
ASX Clear. Margin Methodology for Equity Options. ASX, accessed 2026.
Local reference on initial and variation margin for written put positions on ASX-listed equities.

How to cite this page

Dr. Phil's Quant Lab. (2026). Short Put. Derivatives Atlas. https://phucnguyenvan.com/concept/short-put