# OASDI modeled liabilities and benefits Six outputs report modeled OASDI liabilities, modeled OASDI benefits and their difference, the modeled balance. They add up existing variables and change no other output. The balance compares modeled liabilities with modeled benefits; it is not a trust-fund cash balance. ## Definitions | Output | Entity | Definition | | --- | --- | --- | | `oasdi_payroll_tax_revenue` | Person | `employee_social_security_tax + employer_social_security_tax + self_employment_social_security_tax` | | `oasdi_benefit_taxation_revenue` | TaxUnit | `tob_revenue_oasdi` | | `oasdi_niit_revenue` | TaxUnit | `s770_revenue_oasdi` | | `oasdi_income` | Household | Each member's `oasdi_payroll_tax_revenue`, plus each tax unit's `oasdi_benefit_taxation_revenue` and `oasdi_niit_revenue`, each counted once | | `oasdi_cost` | Household | Members' public `social_security`, after any enabled benefit policies | | `oasdi_modeled_balance` | Household | `oasdi_income - oasdi_cost` | The payroll leaves read their rates and the wage base from parameters: `gov.irs.payroll.social_security.rate.employee` and `.employer` apply to wages up to `gov.irs.payroll.social_security.cap`, and `gov.irs.self_employment.rate.social_security` applies to self-employment net earnings in the room that wages leave under the base. A reform that replaces a leaf reaches the sum through that leaf. The owners' draw reform's `self_employment_social_security_tax` adds `owners_draw_oasdi_tax`, so the draw's OASDI tax counts once; don't add it again. `oasdi_benefit_taxation_revenue` is the OASDI share of income tax on benefits. It measures `income_tax_chapter_1`, chapter 1 liability after nonrefundable credits and before refundable credits. The share is that liability with section 86 inclusion as before the 1993 amendments, capped at actual inclusion, less the liability with no inclusion. At current law the cap changes nothing. When a reform cuts inclusion below the pre-1993 amount, the 1993 amendments add nothing, so OASDI takes the whole increase. The HI share, `tob_revenue_medicare_hi`, stays out. The share carries a sign: a unit whose tax falls when its benefits enter income contributes a negative amount, so sum units without a floor. `oasdi_niit_revenue` is the OASDI transfer that the enabled S.770 section 8 options select. It is zero unless an option applies, and it counts only the transfer, not the whole `net_investment_income_tax` liability. See the [S.770 section 8 README](https://github.com/PolicyEngine/policyengine-us/blob/main/policyengine_us/reforms/congress/s770/README.md) for the transfer modes. ### Flows left out * `employer_total_social_security_tax` applies the employer rate to `employer_total_taxable_earnings_for_social_security`, a separate input for employer-only payroll tax calculations that defaults to zero, rather than to a worker's own wages. Where data populate both, they describe the same employer liability, so the sum keeps only the worker-level `employer_social_security_tax` and the aggregate is not a fourth stream. * `unreported_payroll_tax`, the tax on unreported tips and wages from Forms 4137 and 8919, is a TaxUnit input that doesn't separate OASDI from HI. * `employer_ss_tax_income_tax_revenue`, the income tax on employer OASDI contributions under the contributed reform that counts employer payroll tax as income, isn't part of `oasdi_income`. A score that enables that reform adds it separately. ### Benefit taxation and the NIIT transfer `tob_revenue_oasdi` takes the difference in `income_tax_chapter_1`, which leaves out `net_investment_income_tax`. Including benefits raises adjusted gross income and so `niit_magi`, so benefit inclusion can trigger NIIT. The trust fund transfer covers only chapter 1 income tax liabilities, and the NIIT sits in chapter 2A, so that NIIT stays out of the benefit taxation term. With an S.770 section 8 option on, `oasdi_niit_revenue` transfers shares of the section 8 add-on and active taxes, and in bill or combined-rate mode of the existing-rate NIIT. Benefit inclusion can raise those taxes too. `oasdi_income` counts the transferred share of that increase once, in the NIIT transfer term. ## Entity mapping and weights `oasdi_income` credits each tax unit's amount once, to the household of its first member. `Microsimulation` weights a tax unit by that same household's weight, so household-weighted totals equal the Person and TaxUnit weighted totals. PE-US declares that tax units sit inside households, and the chunked helper below requires it. If data ever breaks that nesting, the first-member credit still keeps the weighted totals equal. Core's group-to-group `adds` would instead split a tax unit's amount equally among its members and credit each member's share to that member's household. When you aggregate, sum each output at its own entity with that entity's weights, once. Don't project a tax-unit amount to its members and sum it again: `calculate("oasdi_benefit_taxation_revenue", map_to="person").sum()` counts a married couple's amount twice. ## Stated limitations This page states these limitations without measuring them. No residual from another model closes them. **Missing cash flows.** The modeled balance leaves out interest on trust fund reserves, the Railroad Retirement financial interchange, administrative expenses and general-fund reimbursements. None of these flows is a model variable. **Recipients outside the frame.** `oasdi_cost` sums benefits for the people in the household dataset. The dataset misses or only partly represents beneficiaries outside its frame, such as those living abroad. **Noncovered employment.** `payroll_tax_gross_wages` is employment income less FICA pre-tax contributions, with no general OASDI-coverage flag. The model therefore taxes wages from employment that OASDI doesn't cover, such as some state and local government jobs, as covered wages. This wage-coverage assumption differs from the missing cash flows. **Pass-through classification in the scoring data.** The owners' draw term in payroll liability and `oasdi_niit_revenue`, in both its NII and active parts, depend on pass-through classification fields. The certified artifact's stored columns don't include `passive_partnership_s_corp_income`, which therefore defaults to zero. Population values for those two terms stay provisional until a scoring artifact carries the repaired fields and the preflight receipt confirms them; the [S.770 section 8 README](https://github.com/PolicyEngine/policyengine-us/blob/main/policyengine_us/reforms/congress/s770/README.md#scoring-data-limitation) describes the repairs. ## Scoring a population 1. **Audit the stored data first.** Run the [scoring-data preflight](social-security-scoring-preflight.md) on the exact H5 you'll score: ```bash python -m policyengine_us.tools.social_security_preflight /data/populace_us_2024.h5 > receipt.json ``` It checks the artifact's hash and base year and the four benefit components' sources. It also rejects stored columns that would bypass these formulas: the six outputs above, aggregate `social_security`, the worker and employer OASDI tax leaves, the TOB revenue leaves and the `income_tax_chapter_1` they difference, and the NIIT liability and transfer leaves, including the S.770 section 8 and owners' draw tax and OASDI transfer leaves. Keep the receipt with the score. 2. **Score in household chunks.** On main, `tob_revenue_oasdi` recalculates income tax in two branches of the whole simulation, so its working memory grows with the population. Household-chunked calculation, [PolicyEngine/policyengine-us#10561](https://github.com/PolicyEngine/policyengine-us/pull/10561), is the supported route for full-population scoring once it merges. Review may still change its interface, so check its documentation when it lands. Score the same file the preflight hashed. With the interface under review, a call looks like this: ```python from policyengine_us import Microsimulation from policyengine_us.tools.calculate_chunked import calculate_chunked result = calculate_chunked( lambda dataset: Microsimulation(dataset=dataset, dataset_end_year=2035), [ "oasdi_payroll_tax_revenue", "oasdi_benefit_taxation_revenue", "oasdi_niit_revenue", "oasdi_income", "oasdi_cost", "oasdi_modeled_balance", ], 2030, 8, dataset="/data/populace_us_2024.h5", ) totals = result.weighted_sums ``` The helper keeps households whole and requires each tax unit to sit inside one household, so each output's chunk totals add to its population total. 3. **Check the identities on the totals.** The `oasdi_income` total equals the payroll, benefit-taxation and NIIT-transfer totals added together, and the `oasdi_modeled_balance` total equals the `oasdi_income` total less the `oasdi_cost` total. 4. **Treat projected years as independent cross-sections.** The preflight guide describes how `extend_single_year_dataset` projects each year from the base year. Report the limitations above with every score.