Most people first learn options as a way to profit from a big move in a stock.
Selling options introduces another benefit: you can collect premium and potentially profit as the option becomes cheaper over time.
The name for that effect is theta. This week, let’s keep it simple.
What is theta?
Theta estimates how much an option’s price changes when one day passes, with the stock price, volatility and other pricing factors unchanged.
Options have an expiration date. Part of their price is time value: what buyers pay for the opportunity that remains before expiration. As that time runs out, time value generally decreases. Any intrinsic value—what the option would be worth if exercised now—does not disappear just because time passes.
Why sellers like time decay
A buyer pays for an option. A seller collects that payment upfront and accepts an obligation in return.
If the option later becomes cheaper, the seller can buy it back for less. That difference can become a realized profit.
A simple, hypothetical example
You sell one standard option contract for $1.00 per share. With the usual 100-share multiplier, you collect $100.
Later, it trades for $0.50 per share. You pay $50 to buy it back and close the position.
$100 collected − $50 paid = $50 profit before fees.
Time decay can help make that happen. Stock movement and changes in volatility also affect the price, so this example does not promise that theta alone will cut an option’s price in half.
That is one reason I like selling premium: I do not always need a dramatic stock move. Depending on the strategy, a sideways market or a modest favorable move may be enough. I also have the choice to close a profitable trade before expiration rather than wait for every last dollar.
The decay curve
Image: Sabrina Jiang / Investopedia. Source. Read this simplified curve as time value remaining: time value reaches zero at expiration, but an in-the-money option can retain intrinsic value. The curve is illustrative, not a forecast of a live option’s price.
The curve bends more sharply near expiration. This effect is especially pronounced for options near the stock’s current price, known as at-the-money options. Different strikes do not all follow the same decay pattern.
Why 30–45 days is a useful sweet spot
For my selling approach, 30–45 days to expiration is a practical sweet spot. It puts the trade in a window where time decay can increasingly work in the seller’s favor, while leaving time to manage the position.
This is a commonly used starting window, not a magic threshold. Theta is already at work before day 45. Expiration choice is a balance: longer-dated options leave more time on the clock; very short-dated options can decay faster but can also become much more sensitive to a stock move.
tastylive’s DTE framework, for example, favors roughly 45 days as a balance between decay and time for a trade’s assumption to play out.
Time is a benefit—not a guarantee
Selling premium means accepting a trade-off. A covered call limits upside on shares you own. A cash-secured put commits you to buying shares if assigned. A credit spread collects premium while defining a potential loss.
For a spread, I look at the combined position, including the option I bought—not just the theta of the short leg.
I choose the risk first. Then I decide whether the premium is worth accepting it. Theta explains one benefit of selling options; it does not replace that decision.
Keep building a stronger portfolio,
Paul — Mr Premium
Educational content only. Options involve risk. Examples are hypothetical and exclude fees; outcomes are not guaranteed.