What Actually Happens on Expiration Day

Expiration is the one day an option stops being a matter of opinion. The stock closes at a price, the contract resolves, and cash and shares move. For a premium seller it is the day the whole trade was about. It is also the part beginners understand least, because most guides describe it without ever following the money.

So let us follow the money. Pick a closing price below and read the ledger.

There are only three endings

Any option position you hold ends in one of three ways, and it helps to be able to name them.

• You close it early. Buy back what you sold, or sell what you bought, before expiration. Most positions end here. Nothing dramatic happens; it is a trade in the other direction.
• It expires worthless. The contract finishes out of the money, nobody exercises, it disappears. The seller keeps the premium and any collateral is released.
• It is assigned. The contract finishes in the money, the holder exercises, and shares change hands at the strike.

Exercise and assignment are one event with two names

Exercise is what the buyer does. Assignment is what happens to the seller because of it. Same event, two points of view, and the words are not interchangeable. As a premium seller you are always assigned, never exercising.

You do not get a phone call or a choice. Assignment comes through the clearing house overnight, which allocates exercised contracts across the short positions. You find out the next morning when the shares are already in your account.

What assignment does to a put seller

You sold a $100 put and collected $250. The stock closes at $94. You are assigned: $10,000 leaves your account and 100 shares arrive.

Your effective cost is not $100 a share. It is $97.50, the strike less the premium you already collected. The shares show $94 on screen, so you are down $350 on paper. Two different numbers are in play here: the shares are $600 below the strike, and $250 of premium offsets part of that.

This is where the wheel starts. You own shares with a cost basis of $97.50, and the obvious next move is to sell a covered call against them. Keeping that adjusted basis straight over many cycles is hard by hand, and it is most of what Premium Tracker is for.

Compare the second and third rows. Two cents of stock price is the difference between nothing happening and owning $10,000 of stock. In money terms it is nothing. In practical terms it is a lot, and that jump is why the last hour of expiration day matters when a strike is close.

Early assignment happens, but not often

American-style options, which covers almost all single-stock equity options, can be exercised on any day rather than just the last one. It is uncommon, because exercising early throws away whatever extrinsic value is left. A holder who wants out is usually better off selling the contract.

There are two situations where it does happen.

• Short calls before an ex-dividend date. If the dividend is worth more than the time value left in the call, exercising early to collect it makes sense. If you write covered calls, know when your stock goes ex-dividend.
• Deep in-the-money short options near expiry. Once there is almost no extrinsic value left, the holder gives up nothing by exercising.

What can go wrong

Not having the cash. Sell a put without securing it and get assigned, and the shares arrive anyway. The broker funds it as a margin loan and a margin call comes with it. This is how small accounts get hurt.

Assuming a penny in the money will be overlooked. It will not. Automatic exercise has no minimum.

Forgetting assignment fees. Most brokers charge for assignment and exercise on top of commissions. The amount is small, but it lands on exactly the trades that already went against you.

Pin risk. When the stock closes almost exactly on the strike you may not know until well after the close whether you were assigned. Spending a weekend unsure whether you own 100 shares is worth avoiding.