Make all Social Security benefits taxable

[MaxGhenis]

Since Social Security benefits are counted in AGI in a way that makes a flat tax on AGI not a true flat tax (based on other income)

[MaxGhenis]

Actually I was mistaken - the partial inclusion of Social Security benefits applies to gross income, not AGI. So we'd additionally have to make all Social Security benefits taxable. Here's how we can do that:

reform = Reform.from_dict({
  "gov.irs.social_security.taxability.rate.additional": {
    "2024-01-01.2100-12-31": 1
  },
  "gov.irs.social_security.taxability.rate.base": {
    "2024-01-01.2100-12-31": 1
  },
  "gov.irs.social_security.taxability.threshold.base.main.HEAD_OF_HOUSEHOLD": {
    "2024-01-01.2100-12-31": 0
  },
  "gov.irs.social_security.taxability.threshold.base.main.JOINT": {
    "2024-01-01.2100-12-31": 0
  },
  "gov.irs.social_security.taxability.threshold.base.main.SEPARATE": {
    "2024-01-01.2100-12-31": 0
  },
  "gov.irs.social_security.taxability.threshold.base.main.SINGLE": {
    "2024-01-01.2100-12-31": 0
  },
  "gov.irs.social_security.taxability.threshold.base.main.SURVIVING_SPOUSE": {
    "2024-01-01.2100-12-31": 0
  }
}, country_id="us")

In isolation, this reform raises $67 billion in 2024.

[MaxGhenis]

Relies on PolicyEngine/policyengine-us#4830