"Extra" and "Additional" are roughly the same thing, however it is more the context in which they are spoken. "Extra" is an informal word and would be used in casual language. Example: "I want extra cheese on my sandwich." "Additional" is a formal word and would be used more in a business setting.

Additional refers to something added to enhance or complete what is already there, suggesting a necessary or planned extension to meet a specific need or requirement. Extra, however, suggests something beyond the required or expected, often offering more than what is necessary or serving as a bonus.

What is the difference between Extra and Additional? Extra as an adjective is beyond what is due, usual, expected, or necessary; additional; supernumerary. while Additional as an adjective is supplemental or added to.

The most basic difference between these 2 words is all about the necessity. "Addtional" is an complement but it is essential to the composition of a thing whereas the word "extra" indicates something not really essential and being added to another thing. For example: The extra sum of money of this compensation is appro.255 US dollars.