When completing your tax return, it is important to properly classify your business that provided your principal source of income. These codes for the Principal Business or Professional Activity classify sole proprietorships by the type of activity they are engaged in to facilitate the administration of the Internal Revenue Code. These six-digit codes are based on the North American Industry Classification System (NAICS).

Line A of Form 1040 Schedules C and C-EZ requires a Principal Business or Professional Activity description to be entered. Select the category that best describes your primary business activity within the construction industry (refer to the table below). If you owned more than one business, you must complete a separate Schedule C or Schedule C-EZ for each business.

Line B of Form 1040 Schedules C and C-EZ also requires a Principal Business or Professional Activity description to be entered. However, this code should represent the activity that best identifies the principal source of your sales or receipts (i.e. your principal customers or clients). Refer to the table of codes listed below or Instructions for Schedule C, (PDF) Profit or Loss From Business.

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