Option Theta Calculator
Daily time decay of a call or put in currency and as a percent of premium — what one calendar day costs you.
Formula
Theta accelerates as expiry approaches: an ATM option loses value like √T, so the last week burns faster than the previous month. Sellers harvest it, buyers must out-run it with movement.
Not financial advice — for informational and analytical use only. Verify all figures with a qualified professional before acting on them.
Need option theta calculator results fast? Analysts, founders, traders and finance professionals use the Option Theta Calculator to skip the spreadsheet and get a defensible answer in one step — free, private and instant.
About Option Theta Calculator
Daily time decay of a call or put in currency and as a percent of premium — what one calendar day costs you. Theta accelerates as expiry approaches: an ATM option loses value like √T, so the last week burns faster than the previous month. Sellers harvest it, buyers must out-run it with movement. The governing relationship is Θ = −S·φ(d₁)·σ/(2√T) − rK·e^(−rT)·N(d₂) (÷365 per day). The Option Theta Calculator computes entirely in your browser — free, private (your figures never leave your device) and instant, recalculating live as you change any input.
How to use Option Theta Calculator
- 1Enter Spot price, Strike price, Implied volatility (%), Risk-free rate (%), Days to expiry into the Option Theta Calculator.
- 2The result is computed automatically using Θ = −S·φ(d₁)·σ/(2√T) − rK·e^(−rT)·N(d₂) (÷365 per day) — there is no button to press.
- 3Change any input to model a different scenario, then copy or share the result.
Why use Option Theta Calculator?
- ✓Computes option theta calculator instantly with the correct formula — no spreadsheet needed
- ✓100% free and unlimited, with no sign-up, login or paywall
- ✓Runs entirely in your browser, so the figures you enter stay private
- ✓Shows the formula, a live worked example and references so you can defend the number
Frequently asked questions
What is the formula behind the Option Theta Calculator?+
Option Theta Calculator uses Θ = −S·φ(d₁)·σ/(2√T) − rK·e^(−rT)·N(d₂) (÷365 per day). Theta accelerates as expiry approaches: an ATM option loses value like √T, so the last week burns faster than the previous month. The tool substitutes your actual inputs into this relationship and shows the worked example step by step.
What inputs does the Option Theta Calculator need?+
Enter Spot price, Strike price, Implied volatility (%), Risk-free rate (%), Days to expiry and the result updates immediately — there is no button to press. Change any value to model a different scenario in real time.
Is the Option Theta Calculator free, and is my data private?+
Yes — it is completely free with no sign-up or usage limit, and it runs entirely in your browser, so the numbers you enter are never uploaded or stored on any server. It is for informational and analytical use, not financial advice.
What should I watch out for when using the Option Theta Calculator?+
Sellers harvest it, buyers must out-run it with movement.
What is the Option Theta Calculator based on?+
The method follows authoritative sources: Hull — theta of European options. The formula and references are shown on the page so you can verify and cite the result.
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