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What happens if my put option expires in the money?

In the US, an expiring stock option a cent or more in the money is normally exercised automatically unless you or your broker instruct otherwise 1. For a put, that means selling 100 shares at the strike 2. If you own the shares, they are sold; if you don't, exercising leaves you short 100 shares, a position with considerable risk 3.

A put with a $50 strike, bought for its model price with 30 days left at 30% implied volatility (made-up numbers). Set where the stock closes on expiry day, and whether you own the shares.

Source: the StrikePath engine, pricing with the Black–Scholes formula 4 at 4.3% interest a year; a simulated example, not market prices. For learning; not advice.

The automatic exercise

The Options Clearing Corporation exercises an expiring equity option that is $0.01 or more in the money unless instructed otherwise 1. Exercising a put sells the shares at the strike 2.

If you don't own the shares

Then the sale is of shares you don't have: it opens a short stock position, which carries considerable risk and needs the right kind of account 3. Selling the put before it expires keeps its value, at the bid; telling your broker not to exercise it gives that value up. Brokers have their own exercise procedures and cut-off times 5. The put above, priced at $1.63 by the formula 4, is worth more than it cost only below $48.37 at expiry: the strike minus what was paid 3.

What this shows, and what it doesn't

The arithmetic at the close on expiry day, for one contract, before fees. Read your broker's rules for expiry day before it comes.

Go further

Exercise and assignment, step by step →With the deadlines. Part of the full course.What is a put option? →The right to sell, in plain words.
Sources (5), checked 20 October 2026 and 27 October 2026
  1. US Securities and Exchange Commission, Release No. 34-57163 (16 January 2008), approving OCC's change to exercise by exception, 73 FR 4298. Read it (read 20 October 2026)
  2. The Options Industry Council, “What is an Option?”. Read it (read 27 October 2026)
  3. Nasdaq ISE, “Option Strategies: Long Put”. Read it (read 27 October 2026)
  4. Fischer Black and Myron Scholes, “The Pricing of Options and Corporate Liabilities”, Journal of Political Economy 81(3), 637–654, 1973. Read it (read 20 October 2026)
  5. FINRA, “Trading Options: Understanding Assignment” (14 December 2020). Read it (read 27 October 2026)

Now try it on a scenario of your own

Pick where a simulated stock might be, and by when: drag one dot and see, side by side, what buying shares, one option, or a pair of options (a call or put spread) would each do. Free, no sign-up.

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