Taxes are imposed on net income of individuals and corporations by the federal, most state, and some local governments. Citizens and residents are taxed on worldwide income and allowed a credit for foreign taxes. Income subject to tax is determined under tax accounting rules, not financial accounting principles, and includes almost all income from whatever source. Most business expenses reduce taxable income, though limits apply to a few expenses. Individuals are permitted to reduce taxable income by personal allowances and certain non-business expenses, including home mortgage interest, state and local taxes, charitable contributions, and medical and certain other expenses incurred above certain percentages of income. State rules for determining taxable income often differ from federal rules. Federal marginal tax rates vary from 10% to 37% of taxable income. State and local tax rates vary widely by jurisdiction, from 0% to 13.30% of income, and many are graduated. State taxes are generally treated as a deductible expense for federal tax computation, although the 2017 tax law imposed a $10,000 limit on the state and local tax ("SALT") deduction, which raised the effective tax rate on medium and high earners in high tax states. Prior to the SALT deduction limit, the average deduction exceeded $10,000 in most of the Midwest, and exceeded $11,000 in most of the Northeastern United States, as well as California and Oregon. The states impacted the most by the limit were the tri-state area (NY, NJ, and CT) and California; the average SALT deduction in those states was greater than $17,000 in 2014.