un concept de base de la fiscalité
https://en.wikipedia.org/wiki/Tax_basis

--------------------------------------------------
Note added at 3 hrs (2018-01-26 14:14:19 GMT)
--------------------------------------------------

Determining tax basis

The basis of property is generally the property's cost: the amount paid for the property in cash or other property.[2] Holding period refers to the duration of time owned based on the purchase date.[3]

Where an asset is purchased, tax basis generally includes cash paid plus liabilities assumed. For example, if Joe acquires a building for $10,000 cash and assumes a mortgage for $80,000 (which is his liability assumed), Joe's basis in the building is $90,000. If multiple items of property are acquired together in a single transaction, the tax basis must generally be allocated to the items in proportion to their values at the time of acquisition.[4]

Fungible property (e.g., bushels of wheat or shares of corporation stock) may include items of property acquired at different times with differing bases. If such property is sold, the taxpayer may need to use an assumption (such as average cost or FIFO) for determining the cost of the portion of the property sold.

Adjustments to basis

The tax basis of an asset subject to cost recovery must be reduced by deductions allowed for such cost recovery.[5] For example, if Joe claimed $25,000 of depreciation deductions on his building, his adjusted basis would be the $90,000 as above less $25,000, or $65,000. Cost recovery deductions may include depreciation, amortization, and deducted losses or declines in value. Some jurisdictions (e.g., Germany) allow a deduction for decline in value of certain assets, which reduces tax basis.

Source: Wikipedia