What is theta in options?
Updated 13 June 2026 · by Theo Chen
Theta measures how much value an option loses each day from time passing alone. An option with a theta of −0.05 sheds about $5 per contract a day. For the buyer that decay is a cost; for the seller it is income — which is why a covered call or cash-secured put earns even when the stock does nothing.
Want theta per day for a specific option, with the other Greeks beside it? Enter the inputs and the Black-Scholes calculator returns theta, delta, gamma and vega for any strike and expiration.
Open the Black-Scholes Calculator →Why is theta the seller's engine?
Every option's price has two parts: intrinsic value (how far in the money it is) and time value (everything else). Theta measures the daily melt of that time value. When you sell an option you collect the full time value up front, then theta works in your favour every day the stock behaves — you can buy the option back cheaper, or let it expire worthless and keep the whole premium. This is the structural edge premium sellers harvest: they are, in the jargon, "long theta."
Why isn't theta decay linear?
Time decay speeds up as expiration approaches. An at-the-money option loses time value slowly when it is months out and rapidly in its final weeks — the decay curve bends sharply at the end. That shape explains a common seller's choice: open trades around 30–45 days to expiration to sit in the steepening part of the curve, and often close them early once most of the premium has decayed, rather than holding into the last whippy days. The deeper treatment is in theta decay explained.
The catch: theta is paid for risk
Theta is not free money. The decay you collect near expiration comes bundled with high gamma — your directional exposure (delta) can swing violently in the final days, so a calm short option can turn into a loss fast on a sharp move. Theta also rises with implied volatility: higher vega means more premium, hence more theta to decay, but also a bigger expected move. You are being paid theta to carry gamma and vega risk — the seller's whole job is keeping that exchange in your favour.
A worked read
You sell a 30-day at-the-money call showing a theta of −0.06. If the stock sits still, the option loses about $6 a day in value — money you keep as the short seller. Over a quiet week that is roughly $42 of decay working for you, before any move in the stock. Watch how theta climbs as the same option nears expiration using the Black-Scholes calculator.
The bottom line
Theta is not free money - the daily decay a seller collects is paid in exchange for gamma and vega risk, and it accelerates in the final weeks, which is why many sellers open trades 30-45 days out and close winners early.
Frequently asked questions
What is theta in options trading?
Theta measures how much value an option loses per day purely from the passage of time, holding everything else constant. An option with a theta of −0.05 loses about $5 per contract each day (0.05 × 100). For the buyer that decay is a cost; for the seller it is income, which is why theta is the engine behind premium-selling strategies.
Is theta good or bad?
It depends which side you are on. If you bought the option, theta works against you — every day that passes erodes your premium. If you sold the option, theta works for you — that same erosion is profit, because you can buy the option back cheaper or let it expire worthless. Covered call, cash-secured put and credit spread sellers are all "long theta."
When is theta decay fastest?
Time decay accelerates as expiration nears, and is fastest in the final few weeks for at-the-money options — the decay curve is steep, not linear. This is why many sellers favour 30–45 days to expiration: it captures rich decay without the whippy gamma risk of the last days, and why many close winners early rather than holding into the final stretch.
How does theta relate to the other Greeks?
Theta and gamma are a trade-off: the high decay a seller collects near expiration comes with high gamma, meaning delta (directional risk) swings fast. Theta also depends on volatility — higher implied volatility means more premium and therefore more theta to decay. You are paid theta for taking on gamma and vega risk.
Do all options have the same theta?
No. At-the-money options have the most theta because they have the most time value to lose. Deep in- or out-of-the-money options have less time value, so less to decay. Theta also grows as expiration approaches and shrinks for longer-dated options like LEAPS, which decay very slowly day to day.
Related questions
- Why does theta decay accelerate near expiration?
- What is gamma, the risk theta pays you to carry?
- What is vega and how does it tie theta to volatility?
- Which Greeks matter most when selling options?
Related tools and guides
Theta is one of five. Read the others — delta, gamma and vega — plus the full treatment in theta decay explained and the Greeks for option sellers. See theta per day for any option in the Black-Scholes Calculator.
Educational information only — not financial advice. Theta assumes all else held constant; in reality a move in the stock or a change in volatility can swamp a day's decay.