An option has a deadline, and that deadline is always getting closer. The slow erosion of an option’s extrinsic value as expiry approaches is called time decay.
The melting ice cube
Picture the extrinsic part of the premium as an ice cube. Every day, a little melts. At expiry, it’s gone completely — all that’s left is intrinsic value (which may be zero).
Crucially, the melt isn’t linear. It speeds up as expiry nears:
- A 90-day option loses time value slowly.
- The last few weeks decay much faster.
- The final days can evaporate what’s left.
Theta
The Greek that measures this is theta — roughly how much value an option loses per day, all else equal.
- If you’re long an option, theta is working against you. You need the stock to move enough to outrun the decay.
- If you’re short an option, theta is working for you — time passing is literally money.
What happens at expiration
At expiry, an option settles based purely on intrinsic value:
- In the money → it has value and is typically auto-exercised by your broker.
- Out of the money → it expires worthless. The premium is gone.
- At the money → it’s a coin-flip zone (this is where pin risk lives for sellers).
Putting it together
This is the buyer’s central tension: you pay extrinsic value up front, and time relentlessly drains it. Be right, big enough, and soon enough. Sellers take the opposite bet — that not much happens before the ice cube melts.
Open the payoff playground, pick a long call, and drag the days-to-expiry slider down — watch the smooth “today” curve collapse onto the kinked expiry line. That collapse is time decay.