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If you are selling assets not shares of your C-corporation...
Both the buyer and seller involved in the sale of business assets must report to the IRS the allocation of the sales price among section 197 intangibles and the other business assets. Use Form 8594, Asset Acquisition Statement Under Section 1060, to provide this information.
The sale price for used equipment and fixtures should be fair market values of these assets - on which both the buyer and the seller agreed - not book values.
The buyer and seller should each attach Form 8594 - http://www.irs.gov/pub/irs-pdf/f8594.pdf to their federal income tax return for the year in which the sale occurred. See also instructions - http://www.irs.gov/pub/irs-pdf/i8594.pdf
When sold, these assets must be classified as capital assets, depreciable property, real property, intangible property (including goodwill, non-compete agreement, patents, franchise, trademark, trade name), or property held for sale (inventory or stock in trade).
The gain or loss on each asset is figured separately. The sale of capital assets results in capital gain or loss. The sale of real property or depreciable property used in the business and held longer than 1 year results in long term gain or ordinary loss. The sale of inventory results in ordinary income or loss.
The sale of real property or depreciable property used in the business and held longer than 1 year results in long term gain or ordinary loss. The sale of inventory results in ordinary income or loss.
Self-created assets generally do not qualify for long term capital gain treatment.
To estimate your possible tax liability - you need to do following;
(1) list all your business assets
(2) assign the sale price to each asset
(3) determine the basis for each asset
Some gain will be taxed as long term capital gain and some as ordinary income
Let me know if you need help with estimations.