If you are in business for yourself, or carry on a trade or business as a sole proprietor or an independent contractor, you generally would consider yourself self-employed and you would file IRS Schedule C, Profit or Loss From Business or Schedule C-EZ, Net Profit From Business with your Form 1040.

Here are five things the IRS wants you to know about self-employment:

 1.     Self-employment can include work in addition to your regular full-time business activities, such as part-time work you do at home or in addition to your regular job.

 2.     If you are self-employed you generally have to pay Self-employment Tax. Self-employment tax is a social security and Medicare tax primarily for individuals who work for themselves. It is similar to the social security and Medicare taxes withheld from the pay of most wage earners. You figure SE tax yourself using a Form 1040 Schedule SE. Also, you can deduct half of your self-employment tax in figuring your adjusted gross income. 

3.     If you are self-employed you generally have to make estimated tax payments. This applies even if you also have a full-time or part-time job and your employer withholds taxes from your wages. Estimated tax is the method used to pay tax on income that is not subject to withholding. If you don't make quarterly payments you may be penalized for underpayment at the end of the tax year.

4.     You can deduct the costs of running your business.

These costs are known as business expenses.  In the current year you may deduct business expenses, such as: advertising, office expenses, rent, travel, repairs and maintenance, and many more.

5.     To be deductible, a business expense must be both ordinary and necessary. An ordinary expense is one that is common and accepted in your field of business. A necessary expense is one that is helpful and appropriate for your business. An expense does not have to be indispensable to be considered necessary. 

IRS Tax Tips E-Newsletter article of January 24, 2011.