Paying Interest Only What Advantage Is There To Paying Extra On An Interest Only Mortgage?

What advantage is there to paying extra on an interest only mortgage? - paying interest only

I took a 5 / 1 home loan interest until last year for $ 400,000 (I could not) the authorization for a fixed rate loan at that time and pay monthly payments of $ 2,000. Since then, our household income increased significantly and I believe an increase in the amount of $ 2,500 per month with the hope that over $ 500 is going to principal. I do not even know to think about refinancing, because you have just bought less than a year ago, but I have my extra income for a good cause. Good idea or bad?