The difference is profit for the exchange. They usually expire on the third Friday of their expiration month. You should sell near-month call options. This results in higher yields than if you write calls with expirations two or more months out. Sometimes the stock price goes up and the option premium goes down, or vice versa.
Option premiums tend to decline as their option expiration date approaches.
To get the best yield, access to current premium pricing information is imperative when the option is sold. This amount appears in the option premium but is not really a true premium because the option strike is lower than the purchase price of the stock. It would be a positive yield if the option is not called. Likewise, to uncover the highest yields, we also compare pure premium yield on options for different expiration months. This list contains multiple option expiration months, sorted by pure daily premium yield with the highest yields at the top.