Guidelines for support orders may be based on laws that require obligors to pay a flat percentage of their annual income toward their children's expenses. Often two approaches are combined. In the United Kingdom, for instance, there are four basic rates of child support based on the obligors' income, which are then modified and adjusted based on several factors. In the United States, the federal government requires all states to have guideline calculations. Guidelines are either a percentage of income or more usually in the form of tables listing incomes and the amount needed to support one to six children. These computations are often performed by computer programs upon input of certain financial information including, earnings, visitation (overnights with the non-custodial parent (NCP)), health insurance costs, and several other factors.