I signed up to present at a conference and didn't tell my advisor about it. How to handle this now? I have a little bit of the dilemma here... A month ago, I signed up for a conference talk and I got accepted to present there... However , I actually found out about that conference and decided on my own to give a talk... I did not tell my advisor about it. At that moment, I did not think much. And part of me forgot about it since I was so busy with everything else.

Now, thinking back, it occurs to me that I might have done something stupid. From what I know , most PhD students go to and give talk at conferences because their advisors tell them to go... So I am not sure if I did the right or the wrong thing not asking my advisor before applying to go... 

So I know that I now should tell my advisor about the conference. However, I am not sure how I should explain about that fact that I didn't ask before applying ... Is it common for graduate students to let the advisors know before applying for a conference ? Seems like it is a common thing at my institute. 

Or should I just back out from the conference? I don't think it is smart if I back out since it will hurt the reputation. 

Please give me some insights about this. Thanks a lot.
Explain it just like you explained in your post.

Tell your advisor that you are very interested in attending a particular conference and that you even applied. You realized it was an oversight that you applied without talking to him first, and then you got sidetracked.

Make it clear that you want to go, that you got accepted, that you made a mistake, and you'd appreciate his feedback on all of it. If your advisor tells you to withdraw, then I would probably listen.

It is not common to do such a thing without discussing it with your advisor, often because they are a co-author and footing the bill.