What Is Theta in Options? Time Decay in Dollars per Day
Reviewed by Leon Moyer - Published October 9, 2026 - Last reviewed October 9, 2026
In this lesson
Use theta to estimate how much value an option will lose over a period of days, and explain why time decay speeds up as expiration approaches.
Theta estimates the change in an option's price as one day passes, with all other pricing inputs fixed. It is usually negative for buyers and positive for sellers. The usual loss of value with time is called time decay or theta decay. The sign is not universal: a deep-in-the-money European put can have positive theta because the discounted strike payment grows toward its full value as expiration nears.
Every option has an expiration date, so every bought option is racing the clock. Theta turns that race into a dollar figure you can plan around. This lesson uses the module's standard inputs: XYZ at $50, the XYZ 50 call with 30 days left, 30% implied volatility and a 4.5% interest rate.
What is theta decay?
An option's price has two parts. Intrinsic value is what it would be worth if exercised right now. Time value is everything above that: what buyers pay for the chance that the stock moves further before expiration. At expiration, time value is gone, so an option is worth only its intrinsic value. Theta measures the daily pace of that disappearance.
The XYZ 50 call with XYZ at $50 is at the money, so it has no intrinsic value. All of its $1.81 per share ($181 per contract) is time value. If XYZ sits at exactly $50 until expiration, the whole $181 drains away. Its theta says how fast: about $0.03 per share, or $3.16 per contract, per day right now.
In one sentence: estimated price change from time = theta per share x 100 x contracts x days, as long as nothing else changes and the period is short.
Worked example
Holding the XYZ 50 call for a week with the stock flat
You own one XYZ 50 call, which the model values at $180.58 per contract (inputs above). Its theta is -$3.16 per contract per day. XYZ stays at $50 and implied volatility stays at 30% for a week.
- Theta's estimate: 7 days x $3.16 = $22.12.
- The model's value with 23 days left: $157.15.
- The repriced model loss: $180.58 - $157.15 = $23.43.
The estimate comes in a little low because theta is not constant: its magnitude grows a little every day as expiration gets closer. Adding up each day's theta separately gives $23.22, much closer to the repriced model loss.
Illustrative and hypothetical. The ticker and prices are invented for teaching, and the figures exclude commissions, fees, margin interest and taxes, which reduce real results. Past or hypothetical outcomes do not indicate future results.
Seven days without the stock moving cost this call about 13% of its value. That is the price of waiting.
When does theta decay accelerate?
Time value does not disappear in a straight line. For an at-the-money option it drains slowly at first and then faster and faster in the final weeks.
Theta: the same call loses more per day as expiration nears
Value per contract
Daily decay rate (negative theta per contract)
The same call, with the stock held at $50, loses $1.94 a day with 90 days left, $3.16 with 30 days left, $6.22 with 7 days left and $15.97 with 1 day left. As a share of what is left, the squeeze is even starker: with 30 days to go the call loses about 1.7% of its value per day, and with 7 days to go about 7.3%.
Theta is a rate measured at one instant, like a car's speed. With a single day left the rate is changing so fast that the figure understates the final day: an option exactly at the money at expiration has zero intrinsic value, so the full $32 of remaining time value disappears.
Does theta affect all options the same way?
No. Theta depends on how much time value an option has to lose, and at-the-money options have the most.
At-the-money options decay the most dollars
Value per contract, 30 days left
Daily decay rate, 30 days left
Daily decay rate, 7 days left
With 30 days left the XYZ 55 call is worth $33 per contract and loses $1.79 a day, less than the 50 call's $3.16 in dollars but a larger share of its value, over 5% a day. In the final week the 55 call is worth only $0.86 per contract, so there is little left to decay: its theta shrinks to $0.48 a day while the at-the-money call's climbs to $6.22.
Deep in-the-money options have small theta too. The XYZ 40 call is worth about $1,015 per contract, almost all of it intrinsic value, and loses only about $0.57 a day.
Why do option sellers like theta?
Because the buyer's loss is the seller's gain. Someone who sold the XYZ 50 call has a theta of +$3.16 per contract per day: if XYZ stays at $50 and IV and rates stay fixed, time decay reduces the cost to close this short call. This is the engine behind the income strategies in Why Traders Use Options, such as covered calls.
The catch is gamma. As What Is Gamma in Options? showed, a seller is short gamma, so a large move in the stock can wipe out many days of collected decay in a single session. Even with a flat stock, rising IV can create a loss. Theta is a model sensitivity, not steady income.
A short call you do not cover with shares has unlimited risk: its loss grows with every dollar the stock rises above the strike. A short put can lose up to the strike x 100 minus the premium.
Does theta decay on weekends and holidays?
The calendar keeps running when markets are closed, so on Monday an option has three fewer days to expiration than on Friday. This module and the OptionsPro calculator count calendar days, including weekends. Decay is not a fixed daily amount: theta changes as time passes. Friday-to-Monday price changes also reflect stock moves, IV and other inputs. OIC notes that models use different decay conventions, so check a platform's units rather than assuming three times Friday's theta is a Monday profit.
Check your understanding
An option has a theta of -$0.05 per share. Roughly how much does one contract lose over 4 days if nothing else changes?
Show answer
About $20. Theta per share x 100 x days: $0.05 x 100 x 4. The repriced loss can be larger or smaller because theta changes; it need not grow for an out-of-the-money option.
Which loses more dollars per day with 7 days left: the at-the-money XYZ 50 call or the out-of-the-money 55 call?
Show answer
The 50 call, at $6.22 per contract against $0.48. At-the-money options hold the most time value, so they have the most to lose each day.
Why is time decay good news for an option seller, and what is the risk that comes with it?
Show answer
A seller with positive theta benefits from time passing if all other inputs stay fixed. The risk is negative gamma: a big move in the stock can cost more than many days of decay.
Key takeaways
- Theta estimates the price change per day with all other inputs fixed: usually negative for buyers and positive for sellers, with exceptions.
- Only time value decays. By expiration it is gone, and an option is worth only its intrinsic value.
- Time decay accelerates for at-the-money options in the final weeks; the example call loses $1.94 a day at 90 days and $6.22 at 7 days.
- Positive theta does not guarantee a seller's profit; stock moves and IV changes can outweigh it.
Common questions
When does theta decay accelerate?
For an at-the-money option, time decay speeds up in the final weeks before expiration and is steepest in the last few days. In this lesson's example the same call loses $1.94 a day with 90 days left, $3.16 with 30 days left and $6.22 with 7 days left.
Does theta decay happen on weekends?
The calendar keeps running over a weekend, so an option has less time left on Monday than on Friday, and pricing models that count calendar days spread decay across every day. A Friday-to-Monday price change need not equal three times Friday's theta: theta changes, other inputs can move, and platforms use different conventions.
Is theta good for option sellers?
Often. Positive theta estimates a benefit from time passing when all other inputs stay fixed; it is not a daily payment or guaranteed profit. The trade-off is negative gamma: a large move in the stock can cost a seller far more than many days of collected decay.
Why is theta negative?
Long options usually have negative theta: their model value falls as time passes with other inputs fixed. This is not universal; deep-in-the-money European puts can have positive theta. A seller takes the opposite sign.