# Theta

> Theta measures how much an option loses in value each day as time passes. Learn how decay speeds up near expiry and why sellers collect what buyers pay.

Source: https://learn.tradelabsai.com/options/theta/  
Track: Options · Level: Advanced · Updated: 2026-10-03  
Publisher: TradeLabs AI (https://tradelabsai.com). Education, not financial advice.  
Cite as: TradeLabs Learn, "Theta", https://learn.tradelabsai.com/options/theta/

Theta measures time decay: how much an option's price is expected to fall each day as expiration approaches, if nothing else changes. An option with a theta of minus 0.05 loses about $0.05 per share, or $5 per contract, each day. Theta is the cost of holding options for buyers and the income of selling them for sellers. Understanding how it behaves is essential for choosing expirations and managing positions.

## Theta basics

| Position | Theta | Meaning |
|---|---|---|
| Long call or put | Negative | Loses value as time passes |
| Short call or put | Positive | Gains value as time passes |
| Highest (in dollars) | At the money options | Most extrinsic value to lose |
| Fastest relative decay | Near expiration | Decay accelerates |

Theta only affects extrinsic value. At expiration, an option is worth its intrinsic value only, so all extrinsic value decays to zero along the way. See [Intrinsic and Extrinsic Value](https://learn.tradelabsai.com/options/intrinsic-and-extrinsic-value/).

## Decay is not linear

The value of an at the money option is roughly proportional to the square root of time left. Halving the time left reduces the value by about 29%, not 50%. As a result, the daily decay grows as expiration approaches.

**Example: Decay by days left**
An at the money call on a $100 stock with implied volatility of 30% has an approximate value of 0.4 × 100 × 0.30 × √(days / 365):

| Days left | Approximate value | Approximate daily theta |
|---|---|---|
| 90 | $5.96 | $0.03 |
| 30 | $3.44 | $0.06 |
| 7 | $1.66 | $0.12 |
| 1 | $0.63 | $0.63 |

The option loses about a cent or three per day at 90 days and its entire remaining value on the last day.

## Theta and moneyness

- **At the money options** have the largest theta in dollars because they have the most time value.
- **Out of the money options** have small dollar theta but can lose a large percentage of their value each day near expiry.
- **Deep in the money options** have little time value and therefore little theta.

## Theta and volatility

Higher implied volatility means more extrinsic value, so more to decay: high volatility options have larger theta. That is why option sellers are drawn to high volatility periods, and why buying options at high implied volatility is expensive in time decay. See [Implied Volatility (IV)](https://learn.tradelabsai.com/volatility/implied-volatility/).

## The theta and gamma trade off

You cannot collect theta without taking on negative gamma. Option sellers earn time decay day after day but lose when the underlying makes big moves. Option buyers pay theta for the right to benefit from big moves. Over time, whether buyers or sellers come out ahead depends on whether actual moves turn out larger or smaller than implied volatility predicted. See [Gamma](https://learn.tradelabsai.com/options/gamma/) and [Volatility Trading](https://learn.tradelabsai.com/volatility/volatility-trading/).

## Weekends and holidays

Option prices decay over calendar time, but markets are closed on weekends. In practice, much of the weekend decay is priced in before Friday's close, so selling options on Friday to "collect weekend theta" is less profitable than it sounds. Different pricing tools also handle weekends differently, so quoted theta can vary.

## Using theta in strategy

| Approach | Theta | Lesson |
|---|---|---|
| Buy options for a big move | Negative: need the move to come soon | [Long Call](https://learn.tradelabsai.com/options/long-call/) |
| Sell covered calls and cash secured puts | Positive | [Covered Call](https://learn.tradelabsai.com/options/covered-call/) |
| Sell iron condors in quiet markets | Positive | [Iron Condor](https://learn.tradelabsai.com/options/iron-condor/) |
| Calendar spreads | Positive: short near month decays faster | [Calendar Spreads](https://learn.tradelabsai.com/options/calendar-spreads/) |
| Long straddles | Negative: need volatility | [Straddle](https://learn.tradelabsai.com/options/straddle/) |

Many option sellers open trades with 30 to 45 days to expiry and close them with 1 to 3 weeks left, aiming to capture decay while avoiding the very high gamma of the final days. See [Theta Harvesting](https://learn.tradelabsai.com/options/theta-harvesting/).

## Common mistakes

- **Buying short dated options** and watching them decay before the move happens.
- **Thinking theta is easy income for sellers.** It is payment for taking on gamma risk.
- **Ignoring theta on long option positions held for weeks.**

## Frequently asked questions

### What is theta in options?

The expected daily loss in an option's value from the passage of time, assuming price and volatility stay the same.

### Why does time decay accelerate near expiration?

Because an option's time value is roughly proportional to the square root of time left, so each day removes a larger share of what remains.

### Do option sellers always profit from theta?

No. They collect theta, but large moves in the underlying can cause losses that exceed the decay earned.

Next, learn how volatility changes option prices in [Vega](https://learn.tradelabsai.com/options/vega/).

## Continue learning

- Next lesson: [Vega](https://learn.tradelabsai.com/options/vega/)
- Previous lesson: [Gamma](https://learn.tradelabsai.com/options/gamma/)
- Related: [Gamma](https://learn.tradelabsai.com/options/gamma/): Gamma measures how much an option's delta changes for a $1 move in the underlying. Learn why gamma peaks at the money near expiry and how it drives risk.
- Related: [Intrinsic and Extrinsic Value](https://learn.tradelabsai.com/options/intrinsic-and-extrinsic-value/): An option's price splits into intrinsic value and extrinsic or time value. Learn how to calculate each, what drives extrinsic value and why it decays to zero.
- Related: [Theta Harvesting](https://learn.tradelabsai.com/options/theta-harvesting/): Theta harvesting sells options to collect time decay and the volatility risk premium. Learn the evidence, the common structures and how to survive the tail risk.
- Related: [Option Expiration Dates](https://learn.tradelabsai.com/options/option-expiration-dates/): Every option has an expiration date when it must be used or expire. Learn monthly, weekly and 0DTE cycles, what happens at expiry and how to choose an expiration.
- Related: [Vega](https://learn.tradelabsai.com/options/vega/): Vega measures how much an option's price changes for a 1 point move in implied volatility. Learn how it varies by expiry and why it matters around events.