Theta Decay: How Options Lose Value Over Time

In short

Theta measures an option's daily value loss from time passing alone, and that decay isn't linear — it accelerates sharply as expiration approaches, shown across a 60-day option life.

Every option pays rent just to exist. Theta is the daily bill, and it's not a flat fee.

What theta measures

Theta measures how much value an option loses per day from time passing alone — no price move, no volatility change, nothing else. It's often called "rent." Unlike rent, the payment grows as the lease runs out.

A worked example across a 60-day life

An at-the-money call on XYZ, tracked at three points in its life:

Days to expiration	Option price	Theta (daily decay)
60	$4.20	-$0.03
30	$2.90	-$0.06
7	$1.10	-$0.14

With 60 days left, the option loses about 3 cents a day. With 7 days left, it's losing 14 cents a day — nearly five times faster, even if the stock hasn't moved at all. The price dropped from $4.20 to $1.10 over 60 days, but not evenly.

Why decay speeds up instead of staying flat

Time value reflects how much room the stock still has to move favorably before expiration. Early on, there's a lot of that room left, so losing a day barely dents it. Near expiration, that room shrinks fast — each remaining day is a bigger slice of what's left, so it costs more.

Why this cuts differently for buyers and sellers

An option buyer fights theta the whole time they hold the position — every day without a favorable move works against them, and it gets worse the closer to expiration. A seller collects that same decay; time passing with no adverse move is exactly what they want. That's why income strategies like covered calls and cash-secured puts, taught elsewhere in this Learning Library, are built around selling options and letting theta work for you.

Theta assumes everything else stays still, but price and volatility rarely do. A rally can offset several days of decay in an afternoon; so can a volatility spike. Theta is one force on an option's price, not the only one — and a seller isn't automatically protected either, since a large sudden move can overwhelm any theta collected.

Key takeaway: theta decay accelerates as expiration nears — options lose value faster in their final days than in their first.

Next: gamma and vega — the two Greeks that round out the full picture, covered here in two short lessons.

This lesson is educational content explaining standard options mechanics, not personalized investment or trading advice.