+0
Wow! This house is huge and it has six bedrooms. It's good to have a couple of extra/additional bedrooms.

Don't driving around with unnecessary load in the trunk. It consumes additional/extra fuel.

What's the difference between additional and extra? Thanks in advance!
+0
To me, Additional means a number has been added to the basic number. Extra often means beyond what is necessary or needed. Additional room may be needed; extra room may never be used. Compare these to "spare." A spare tire or a spare room may never be used, but they have the specific purpose of being available in an emergency. Often when something is "extra" you get rid of it.
Comments  
Students: Are you brave enough to let our tutors analyse your pronunciation?
New2grammar.

Don't driving around with unnecessary load in the trunk. It consumes additional/extra fuel.

What's the difference between additional and extra? Thanks in advance!

No, in this context, to me extra means spare. "additional" will mean beyond the existing six bedrooms.

Wow! This house is huge and it has six bedrooms. It's good to have a couple of extra/additional bedrooms.

"The dinner doesn't come with dessert and coffee. You may order for extra / additional charge". In this context, they have the same meaning.
Language seems to change constantly. When panhandlers first started saying, "You got any spare change?", I thought, "What are they talking about? Now I know.

Purists are fighting a losing battle.