If you have another source of income which you have indicated that you do, then you should file a  personal return Form 1040.  Depending on your state's rules about single member LLC you may have to file a return to report the income of the LLC.  For Federal purposes the SMLLC is a  disregarded entity which means that the income or loss from the SMLLC would get reported on your personal reutrn Form 1040 on Schedule C, and no other Federal return is required.  If you are having to prepare a personal return Form 1040 anyway because of your other income, you should report your income or loss from your SMLLC on your personal return Form 1040 Schedule C.  If you have a loss from the SMLLC it could reduce your overall taxes.  It is always a good idea to file the return. (This post was edited to remove a link. Please review our Community Best Practices for more information about how best to participate in our online discussions. Thank you.)

The $400 figure refers to self employment tax. There is no self employment tax (different than income tax) if you do not make over $400 in profit from your business. You still must file. No one can tell you if you need to pay qrtly estimated taxes without looking at your entire tax picture, including money from other job, amount of tax withheld, exemptions and deductions you have all factor into wether or not you have to pay quarterly.

I also own a single member LLC. I file my taxes using a Schedule C with my personal taxes. If you make less than $400, you don't need to file, but you should anyway if you intend to keep the business active. By fling, you can deduct your expenses as well as reporting income, which might result in a business loss and help with your overall tax burden. You will not be able to take a loss year after year, however, without raising a red flag and triggering an audit. The IRS expects you to be in business to make a profit and they take a dim view of what might be considered a tax shelter. Whether you need to pay quarterly estimated taxes will depend on the amount of income from the business. The IRS requires that you pay 90% of the taxes you will owe, either through withholdings from your regular employment or by paying estimated taxes. Some years I pay estimated taxes and other years I don't. The last couple of years I have received a tax refund, so there was no need to pay estimated taxes and have the money returned to me. If I am pretty sure I would owe, then I make the estimated tax payments. There is no set amount you must pay in estimated taxes, so you can pay as much or as little as you choose as long as at least 90% of your total tax liability is paid. If you regularly receive a tax refund, then you probably won't need to pay estimated taxes, or much tax. If, however, you usually owe, then you should make at least one estimated tax payment. When you are a single member LLC and you currently have little income, it would be silly to be taxed as a corporation. As an LLC, you should leave the profits in the business (sole proprietorships also leave the money in the bank; they don't take it out each year). If you haven't opened a business bank account and obtained an EIN, you should do that. You will use the EIN as the identifying number on the bank account, not your SS#. If you are serious about the business, it should be conducted like a business. Otherwise, the IRS can declare it to be a hobby, not a real business.

nice....