What is theta?
Theta estimates the change in an option’s theoretical price from one day passing, all else equal. A long call generally has negative theta. If theta is -0.05, the model suggests approximately $0.05 per share—or $5 per standard contract—of daily value loss under unchanged conditions.
Where does decay come from?
Time value reflects the possibility of a favorable future move. Each passing day removes opportunity. At expiration, time value becomes zero and the call is worth only intrinsic value, if any.
Time decay is not linear
Decay is usually slower when substantial time remains and often becomes more intense near expiration. Near-ATM options can experience particularly visible acceleration because much of their premium is time value.
| Time remaining | General pressure | Buyer consideration |
|---|---|---|
| Several months | Usually slower daily decay | Higher initial premium |
| Several weeks | Increasing | Thesis needs progress |
| Final days | Often intense | Little recovery time |
Example
A call costs $3.00 with theta of -0.04. If all else truly stayed equal, one day would reduce theoretical value to about $2.96. Over several days, theta itself changes, so multiplying one reading by many days is only a rough estimate.
Expiration selection
Short-dated calls cost less but place more pressure on timing. Longer-dated calls cost more but allow the thesis more time. Use the expiration-selection guide to compare the trade-off.
Managing theta risk
- Choose enough time for the thesis.
- Avoid holding by default into the fastest-decay period.
- Define a time exit before entry.
- Monitor time value, not only stock direction.
- Keep total premium risk within the position plan.
Frequently asked questions
Does theta apply on weekends?
Models incorporate calendar time, but market prices adjust continuously and do not necessarily show a simple fixed weekend deduction.
Can a call rise despite negative theta?
Yes. A favorable stock move or volatility increase can exceed the effect of time decay.
Continue the series
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Options involve risk. Educational content only; not investment advice.