Why Is Theta Decay Generally Non-Linear, Accelerating Closer to Expiration?

Theta decay accelerates closer to expiration because the probability of the underlying price moving significantly to make an OTM option ITM, or an ITM option deeper ITM, diminishes rapidly. The time value, which is essentially the premium paid for that remaining uncertainty, collapses quickly in the final weeks.

This non-linear decay is a key feature of option pricing.