Theta decay over time

Theta is the Greek that governs time decay, the daily erosion of an option's extrinsic value as it moves closer to expiration. It's the core mechanic that makes options selling a viable income strategy, and it's the force that continuously works against options buyers.

Understanding how theta behaves over time, specifically how it accelerates, is essential for structuring trades and timing entries and exits.

What theta measures

Theta is expressed as the dollar amount an option loses per day. An option with a theta of −0.05 loses $5 per day per contract (−$0.05 × 100 shares).

This decay comes entirely from extrinsic (time) value. Options have two components of value:

• Intrinsic value: How far the option is ITM right now. This doesn't decay.
• Extrinsic value: Time + volatility premium. This decays to zero by expiration.

Theta measures the daily rate of that extrinsic value erosion.

Theta is not linear, it accelerates

This is the most important thing to understand about theta: it doesn't decay at a constant rate. It decays slowly at first, then rapidly in the final weeks before expiration.

A rough illustration for a 90-day ATM option:

The convex shape of this decay curve is why experienced traders often prefer selling options in the 30 to 45 day window, you're in the steepest part of the decay curve without the extreme gamma risk that comes with 0 to 14 DTE options.

Theta and moneyness

Theta behaves differently depending on where the option sits relative to the stock price:

• ATM options: Have the highest absolute theta. This makes sense, they have the most extrinsic value to decay.
• Deep ITM options: Low theta. Most of their value is intrinsic, which doesn't decay.
• Far OTM options: Low absolute theta but high relative theta, they have little extrinsic value left to lose.

This is why income strategies (covered calls, iron condors, cash-secured puts) typically target ATM or near-ATM strikes, that's where the most time value is available to harvest.

Theta for buyers vs sellers

If you're long options (buyer): Theta is your enemy. Every day that passes, your position loses value. You need the stock to move enough, fast enough, to overcome the daily theta drag. This is why buying options for slow, gradual moves rarely works. You need a significant move before expiration.

If you're short options (seller): Theta is your income. Every day the stock stays within your range, time value erodes in your favor. You're essentially getting paid to wait.

Practical example

You sell a 45-DTE covered call on NVDA and collect $3.00 in premium. The option has a theta of −$0.05.

• Week 1: Option loses ~$1.75 in time value (theta accelerating)
• Week 2: Another ~$2.00 of decay
• At expiry: If NVDA stays below your strike, the option expires worthless, you keep all $300

The closer you get to expiration, the faster the remaining value melts away. If you close at 50% profit ($1.50 remaining value), you've captured the easy part of theta decay and eliminated gamma risk.

The 45-day rule

Many professional premium sellers follow a simple rule:

• Sell options at 30 to 45 DTE (captures the steepest part of decay)
• Close at 50% of max profit (take money off the table, avoid late-stage gamma risk)
• Repeat monthly

This systematic approach to harvesting theta is the foundation of strategies like the wheel, monthly covered calls, and iron condor programs.

Theta and IV

Theta and vega are interconnected. When IV is high, options have more extrinsic value, which means more theta to decay. This is another reason high-IV environments are favorable for sellers: you collect more premium, and more of it decays in your favor each day.

Related terms: Extrinsic value, time value, 0DTE, Vega, gamma, covered call, iron condor

Try it on Stryke: Compare theta values across strikes and expirations in the Options Screener.