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What Is the Mathematical Relationship between Time to Expiration and Theta?

The relationship between time to expiration (T) and Theta is non-linear and inverse. Theta decay accelerates as T approaches zero, following a concave curve.

The mathematical models show that Theta is roughly proportional to $1/sqrt{T}$. This means that an option with 1 day to expiration loses value much faster than an option with 30 days to expiration, even though the time difference is small.

What Is the Mathematical Formula for Calculating Impermanent Loss?
How Does the Basis Typically Behave as a Futures Contract Approaches Expiration?
Why Does Theta Accelerate as an Option Approaches Its Expiration Date?
Why Is Theta Decay Generally Non-Linear, Accelerating Closer to Expiration?