Taxes are most commonly classified as either direct or indirect, an example of the former type being the income tax (inheritance tax, real estate tax) and of the latter the sales tax (value-added tax, excise tax). Direct taxes are taxes on persons; they are aimed at the individual's ability to pay as measured by his income or his net wealth. Income taxes are levied on total personal net income in excess of some stipulated minimum. They are also adjusted to take into account the circumstances influencing the ability to pay of the individual, such as family status, number and age of children, and financial burdens resulting from illness. Income taxes are often levied at graduated rates, that is, at rates that rise as income rises. Inheritance taxes are taxes on the money or property that you give to someone else after you die. Real estate taxes are taxes imposed upon immovable property consisting of land, any natural resources, and buildings. Indirect taxation is a system of collecting taxes by adding an amount to the price of goods and services that people buy. Sales tax is a tax that you have to pay in addition to the cost of something you are buying. Value-added taxes are taxes on the rise in value of a product at each stage of manufacture and marketing. Sales tax levied on the manufacture, purchase, sale, or consumption of a specific commodity is known as an excise tax.