Legal Question in Tax Law in Massachusetts

Re: supplemental business, how should I file?

It is not necessary; depending exactly on how much money you each make and how much the new business will make, plus you expected initial "losses" (also known as start up investment expenses!) it might be better to keep the joint filing. It could also, conceivably, be better to switch. If you want to incorporate the business, you would file a return fo the business entirely separate from your personal return.

There are many different was to organize and different structures for a business entity. You might want to talk this over with an attorney who has experience with corporate / partnership law. You may call me at your leisure at (617)527-0050 if you like, and particularly if you in the Boston area or at least the Eastern half of Massachusetts.

Good luck!