The assessed value of a set of assets, investments or income streams that is subject to taxation, or the assessed value of a single asset that is subject to taxation. Anything that can be taxed has a tax base.

The tax base may refer to that of an individual asset, such as the tax base of a house, or a pool of assets, such as the tax base of all houses in a city. For example, the property tax base of a house is its value. The property tax base of a city is the collective value of all taxable real estate in the city.