Pin Risk: When the Stock Closes at Your Strike
Pin risk is what happens when the stock closes expiration Friday sitting at your short strike — and you spend the weekend not knowing whether you own 100 shares.
It's a narrow risk with a specific shape. Here's exactly where it lives and how to step around it.
What Pin Risk Actually Is
At expiration, the rules look binary: an option $0.01 or more in the money gets auto-exercised, and an option out of the money expires worthless. Clean, mechanical, no ambiguity.
The ambiguity comes from being the seller. When the stock closes right at your short strike — say your short $100 call and a $100.02 close — you don't control what happens next. Exercise is the buyer's decision, and assignment notices arrive overnight. You find out the next morning whether you're short 100 shares or holding nothing.
"Pinning" gets its name from the tendency of heavily-traded stocks to gravitate toward large open-interest strikes on expiration day, which makes closing exactly at a strike more common than chance would suggest.
The Window Where It Lives
The market closes at 4:00 PM ET, but exercise decisions don't. Option holders can submit exercise instructions — including contrary instructions that override the automatic rules — for a period after the close. Broker deadlines vary, typically up to roughly 90 minutes.
That window is where the surprises happen. Your short $100 call finishes at $99.97 — out of the money, expired worthless, done. Then the stock jumps to $100.80 in after-hours trading on a news headline. Holders who are watching can exercise anyway. You can be assigned on an option that "expired worthless" at the closing bell.
The reverse also stings: an option that finished $0.02 in the money gets auto-exercised, you're assigned, and the stock gaps against your new position at Monday's open — a loss that happened entirely while you couldn't act.
Pin Risk on Spreads
Spreads concentrate pin risk because the stock only needs to land between your strikes. Take a $100/$105 bull call spread with the stock closing at $100.02: your long $100 call is exercised — you buy 100 shares — and your short $105 call expires worthless. The defined-risk spread you modeled quietly became $10,000 of stock over the weekend.
Your maximum loss as modeled doesn't change while both legs exist. What changes is what you're holding after expiration — and a stock position carries fresh, unhedged risk the spread never had.
Many brokers auto-close positions with assignment risk on expiration afternoon, on their schedule and at market prices, not yours. That policy is a backstop, not a plan.
How to Take Pin Risk Off the Table
The fix is unglamorous: if a short option is trading near its strike on expiration day, close it before the bell. Buying back a near-the-money short option typically costs a few cents per share. That's the price of knowing what's in your account on Saturday morning.
The rule of thumb: within roughly 1% of a short strike in the final hours, close or roll rather than letting it ride. The premium left to collect is pennies; the position you might inherit is measured in thousands.
Before expiration week arrives, check where your position stands at every price with the Options Profit Calculator — the expiration breakdown shows exactly what happens to each leg at each strike.