Theta and time decay
Last updated: May 30, 2026 · Options Greeks series
Theta is the Greek that makes the entire premium-selling industry possible. It's the daily price erosion an option suffers from time passing — the answer to “how much does this option lose tomorrow if nothing else changes?”
For options buyers, theta is the constant cost of holding a position. For options sellers, it's the steady income that accumulates while you wait. Understanding how theta works — especially how it accelerates near expiration — is fundamental to running any short-premium strategy profitably.
What theta is
Theta is the rate of change of an option's price with respect to time, holding everything else constant. The convention: theta is expressed as a negative number for long options (you lose value daily) or as a positive number for short options (you gain value daily). I'll talk about it from the seller's perspective.
AAPL $195 call, 30 days to expiration, premium $3. Theta = -$0.08.
If nothing else changes overnight, the call will be worth $3 - $0.08 = $2.92 tomorrow. If you sold this call yesterday and bought it back today, you'd make $0.08 in profit purely from time decay (assuming the stock didn't move).
Theta is paid every calendar day, not just trading days. Options decay over the weekend too — one of the small tricks experienced sellers use is to enter Friday afternoon and capture the weekend decay.
Why theta accelerates near expiration
This is the most important practical fact about theta: it accelerates dramatically as expiration approaches for at-the-money options. A 60 DTE ATM call might have theta of -$0.05/day. The same option at 7 DTE might have theta of -$0.30/day — six times faster decay.
Why? Theta represents the daily portion of the option's remaining extrinsic value being burned. With 60 days left, the extrinsic value is large but spread across many days. With 7 days left, the same proportion has to be eaten through faster.
The graph of theta over time isn't linear. It's roughly square-root-shaped: slow early, then progressively faster as expiration approaches. The last week of an at-the-money option is theta-heaven for sellers and theta-hell for buyers.
How premium sellers use theta
The basic premium-selling idea: collect theta. Sell options, let them decay, profit from the decay. Three ways traders do this:
1. Stay in the 14-45 DTE window. This is the sweet spot where theta is meaningful (you're capturing decent daily decay) but gamma — the rate at which delta changes — is still manageable. Outside this window, you're either getting too little theta or too much gamma risk.
2. Take profits at 50% of max profit. The classic rule: once a short option has lost half its value, buy it back and redeploy. The remaining profit per day is small and the gamma risk is rising fast.
3. Avoid the last week. Some experienced sellers close all positions 5-7 days before expiration. The reason: that last week is where gamma risk is highest, and a single bad move can erase weeks of theta gains.
Theta vs gamma trade-off
You can't have theta without gamma. The same options that decay fastest also have the most sensitive deltas. This is the central trade-off in short-premium trading.
Selling weekly options (7 DTE):
- Pro: Very high theta. You're collecting 15-25% of the option's price as daily decay.
- Con: Very high gamma. A small move against you can blow through your strike fast. A 0.30 delta short call can become a 0.70 delta short call in a single day with a 2% move in the underlying.
Selling monthly options (30 DTE):
- Pro: Moderate gamma. Movement against you is digestible.
- Con: Slower theta. Daily decay is smaller per option.
For most income sellers, the 30-day cycle is the right balance. The theta is meaningful, the gamma is manageable, and the trade rhythm is predictable.
FAQ
Does theta accrue on weekends?
Yes, theta is calculated per calendar day. Options decay over Saturdays and Sundays. This is why some traders enter short positions Friday afternoon to capture weekend decay without overnight directional risk.
Why is theta highest at-the-money?
ATM options have the largest absolute extrinsic value, so they have the most value to burn through. Deep ITM and deep OTM options have less extrinsic value and therefore smaller absolute theta — though the percentage decay can still be meaningful.
Can theta be positive?
From the seller's perspective, yes — short options have positive theta because their position gains value as time passes. From the buyer's perspective, theta is always negative (long options lose value to time).
How is theta calculated?
Theta is the partial derivative of the Black-Scholes price with respect to time. The Black-Scholes calculator on this site computes it directly. The full formula involves the cumulative normal distribution; practically, it's enough to know that theta is roughly proportional to the option's remaining extrinsic value divided by the square root of days to expiration.
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