Hi. I'm a late learner but having just passed g5, and wanting to do more, I need to improve my knowledge of music theory. I'm not necessarily asking what the easiest route to getting past the g5 theory exam is since I do want to understand it too but I prefer the online interactive option to the bookworm option. I speak enough languages to not struggle with the nomenclature but I have a hard time with things like chords, intervals and diminished doodahs, etc.

Any advice as to best routes?

What instrument do you play? I'm sure I've read it somewhere but can't remember.
If it's not piano then maybe the first thing to pick up on with chords is that they are arpeggios or broken chords but with all the notes sounding together instead of one at a time.

Intervals are basically how far from one note to the next but you have to remember to count the starting and ending note.... so C to E is a 3rd (C,D,E) F to D is a 6th (F, G, A. B, C, D).

That's the very basics and so the starting point.
I've not used online theory sites so can't comment on which are most useful.

How much theory does your teacher cover in lessons? It may be more than you've noticed and things like intervals and chords can be relatively easily slotted in when learning a piece as things like time signature, key signature, key changes, and performance directions possibly already are.

www.mymusictheory.com is good and free. Certainly a good place to start. Work through the lessons from Grade 1 and see what you know and what is new.

Wow! Great link. Thanks