From the Joint Committee on Taxation's January 2012 projection, here are the top individual categories of lost tax revenue, commonly referred to as tax loss expenditures (the revenue value of tax deductions, tax exclusions, and tax credits), for the five year period from 2011, annualized:
1. Healthcare, healthcare insurance, long term care insurance = $ 145 billion
2. Mortgage interest = $ 93 billion
3. Dividends, long term capital gains = $ 91 billion
4. 401k plans = $ 75 billion
5. Earned income credit = $ 59 billion
6. Pension plans = $ 53 billion
7. State, local income, sales, personal property taxes = $ 46 billion
7. Capital gains at death = $ 46 billion
8. Cafeteria plan benefits = $ 40 billion
9. Untaxed Social Security and Railroad Retirement = $ 38 billion
10. Charitable giving = $ 37 billion
11. State and local government bonds = $ 36 billion
12. Medicare Part A = $ 35 billion
13. Child tax credit = $ 34 billion
14. Life insurance and annuities = $ 30 billion
15. Medicare Part B = $ 27 billion
16. Capital gains on sale of primary residence = $ 25 billion
17. Property taxes on real property = $ 23 billion
Red = housing related ($ 118 billion)
Green = health related ($ 247 billion)
Blue = investment related ($ 137 billion)
Yellow = retirement related ($ 196 billion)
Purple = social welfare related ($ 130 billion)
Black = state and local government related ($ 105 billion)