Summary
Federal SSI living arrangement and related payment logic should eventually be modeled on a monthly basis rather than annually.
Why
Real-world SSI policy is monthly, not annual:
- SSI benefits are computed monthly under 20 CFR 416.420.
- Living-arrangement and ISM determinations are made on a month basis, with first-of-month residence rules in SSA POMS SI 00835.500.
- Key living-arrangement adjustments are explicitly monthly:
- VTR / another person's household: 20 CFR 416.1131
- Medical treatment facility / cap: 20 CFR 416.414
State SSP policy also sits on top of a monthly SSI framework, even when states define their own living-arrangement categories.
Problem
The current federal SSI architecture in the model is annual in places where real policy is monthly. That makes it harder to:
- align federal SSI living arrangement with state SSP logic
- model within-year changes in residence or institutional status
- apply VTR and medical-facility rules in a policy-faithful way
Goal
Introduce a monthly federal SSI payment architecture, with annual values derived from monthly outputs.
Suggested scope
- add a monthly canonical SSI living-arrangement layer
- migrate federal SSI payment-determining variables to monthly where policy requires it
- derive annual SSI totals from monthly values instead of using annual living-arrangement logic directly
- keep state SSP arrangement mapping separate, since states can define additional living-arrangement categories beyond federal A/B/C/D
Non-goals
- do not force all state SSP living-arrangement variables into the federal enum
- do not require all SSI-related status variables to be monthly if they are just stable summary/status flags
Policy references
- 20 CFR 416.420
- 20 CFR 416.1131
- 20 CFR 416.414
- SSA POMS SI 00835.500
- SSA POMS SI 01401.001
Follow-up questions
- Which current federal SSI variables should remain annual summary variables?
- What is the clean migration path that avoids breaking current yearly tests?
- Should we introduce a shared monthly fact/input layer first, then refactor downstream formulas incrementally?
Summary
Federal SSI living arrangement and related payment logic should eventually be modeled on a monthly basis rather than annually.
Why
Real-world SSI policy is monthly, not annual:
State SSP policy also sits on top of a monthly SSI framework, even when states define their own living-arrangement categories.
Problem
The current federal SSI architecture in the model is annual in places where real policy is monthly. That makes it harder to:
Goal
Introduce a monthly federal SSI payment architecture, with annual values derived from monthly outputs.
Suggested scope
Non-goals
Policy references
Follow-up questions