Explain the Relationship between Theta and the Calendar Days Remaining until Expiration

The relationship is inverse and non-linear. Theta is low when there are many days left until expiration, meaning time decay is slow.

As the option gets closer to expiration, the Theta value increases exponentially, causing the rate of time decay to accelerate significantly. This acceleration is often referred to as the "Theta cliff," where the option's extrinsic value plummets in the final weeks.