Theta Decay Visualizer
See exactly how an option loses value over time. Adjust strike, IV, and DTE to watch the characteristic decay curve take shape — and understand why the last 30 days matter most.
Understanding Theta Decay
Theta measures how much an option’s price decreases each day, all else being equal. It is one of the “Greeks” — the risk sensitivities that describe how an option’s value changes with different market variables. For option sellers, theta is your best friend: every day that passes puts money in your pocket as the option you sold loses time value.
Time Value vs. Intrinsic Value
An option’s total price is made up of intrinsic value (how far in-the-money the option is) plus time value (the premium the market pays for the possibility of future movement). Theta only erodes time value — intrinsic value stays the same regardless of time. This is why at-the-money options, which are 100% time value, experience the fastest dollar-amount decay.
Why the Last 30 Days Matter Most
Theta decay is not linear — it follows a curve that accelerates dramatically as expiration approaches. Under Black-Scholes, time value is roughly proportional to the square root of time remaining. That means an option with 60 days left has only about 41% more time value than one with 30 days left (because √60 / √30 ≈ 1.41), even though it has twice the time. The practical consequence: roughly one-third of total time-value decay happens in the final two weeks.
This is why many income-focused traders — especially those running the wheel strategy — target 30-45 DTE when selling options. You capture the steepest part of the decay curve while still leaving room for adjustments if the trade moves against you.
How to Use This Visualizer
Enter a stock price, strike, IV, and expiration to generate a Black-Scholes decay curve. The chart shows the theoretical option value at every day from entry to expiration. The shaded green zone highlights the last 30 days where decay accelerates. Below the chart, the milestone table compares daily theta at key points so you can see exactly how much faster the option loses value as expiration nears.
Try increasing IV and watch the curve shift upward — higher volatility means more time value, which means more total decay. Move the strike further out of the money and notice how the option approaches zero faster: with less intrinsic value cushion, time value is all there is to lose.
Key Formulas
Theta (call) = -(S × N′(d1) × σ) / (2 × √T) - r × K × e^(-rT) × N(d2)
Time Value ≈ Premium × √(DTE / Total DTE)
Daily Theta ≈ Time Value / DTE
Frequently Asked Questions
What is theta in options trading?
Theta measures the daily dollar decline in an option's price due to the passage of time, assuming all other factors stay constant. For sellers, positive theta means you earn money each day. For example, a theta of -$0.05 means the option loses five cents per day.
Why does theta accelerate near expiration?
Time value is proportional to the square root of time remaining. As expiration approaches, each passing day represents a larger percentage of remaining time, so the rate of decay increases. Roughly one-third of total time value is lost in the final two weeks.
What DTE should I sell options at for maximum theta?
Most income traders sell at 30-45 DTE. This captures the steepest part of the decay curve while leaving enough time for adjustments. Selling at 7 DTE gives higher daily theta, but less total premium and more gamma risk.
Does theta decay over weekends?
Options pricing already factors in weekends. Market makers price weekend theta into Friday's close, so the option price drops slightly more on Fridays. However, this is not always visible on the chart because IV changes and stock movement can mask it.
How does IV affect theta decay?
Higher IV means more time value in the option, which means more total decay. A 40% IV option has more theta per day than a 20% IV option at the same strike and DTE. This is why selling options in high-IV environments can be more profitable.
Options involve risk and are not suitable for all investors. All calculations are estimates — actual results will vary. Not financial advice. Full disclosure