Hi,
I'm currently preparing for my Grade 5 guitar practical with Trinity and my Grade 5 violin practical with ABRSM, and my teachers have been talking to me about thinking about doing my theory exams.

I was wondering, do I have to do my Grade 5 theory exam with both boards, or will it be sufficient to do Grade 5 theory with just ABRSM or Trinity?

Either will do.
Just glancing through the Trinity syllabus it has one or two things that are touching on what is in grade 6 AB.
The paper is 3 hours instead of the 2 for AB.
I've not seen a Trinity paper to judge the level.

The Trinity theory exams will be based on a new syllabus next year, but the new syllabus is not on their website. For this year, the existing syllabus is still valid and the past papers for the last few years can be downloaded from the website.

I know that you need ABRSM Grade 5 Theory to progress to ABRSM Grade 6 practical.
Is this also the case with Trinity? (too lazy to check the syllabus...)

Just want to mention that the AB now accept Grade 5 theory from the London College of Music and other exam institutions. That will include Trinity and maybe others from abroad. I will have to find the regulations and check. I will try to find a reference and post it on here

Found it: I'm not sure if I'm allowed to cut and paste here. I followed the FAQ section to an exam syllabus link. Keep going until you get to the regulations page and 1d). The ABRSM exam prerequisites list all the Grade 5's that they now accept.

Trinity Guildhall now don't ask for theory for any practical grades.
I think one, if not both, used to ask for grade 5 if you were doing grade 8 practical.
I think that this is a bit odd as the option to do musical awareness as one of the supporting tests for practical is only available up to grade 5.

Thanks,
I've had a look at both syllabuses and ABRSM does look a bit easier.

Trinity don't seem to say anything about accepting theory from other boards on their website...(correct me if I'm wrong)

I know I won't need my guitar theory yet...but my teacher wants me to get to grade 8 by the time I finish school, and I don't want to waste time over the next two years preparing for another theory exam when I already have A levels to concentrate on!!!!

Just to clarify:

If you want to take AB practical exams beyond Grade 5 the AB require a Grade 5 theory exam - either AB or LCM, Trinity and a few others mentioned on the AB website regulations.

However, if you want to take practical exams beyond Grade 5 with Trinity or LCM you don't need Grade 5 theory until you want to take a Grade 8 with them as you have already said.

It's all very confusing but I hope the above might help.

Good luck