Apply each scheme's own non-dependant test to the LHA shared accommodation rate

[MaxGhenis]

Summary

One variable, lha_renter_has_non_dependant, decided the non-dependant condition of the LHA shared accommodation rate for both Universal Credit and Housing Benefit. It blended the two schemes' definitions, and it treated every 16-year-old as a dependant all year. This PR gives each scheme its own test and drops the 16-year-old rule.

Scheme	Provision	New variable	Person-level definition (from #2017)
UC	Sch 4 para 28(4) with para 9	universal_credit_renter_has_non_dependant	is_benefit_unit_non_dependant_for_universal_credit (16+, not claimant/partner, not a UC qualifying young person)
HB	reg 13D(2)(a)(i) with reg 3	housing_benefit_claimant_has_non_dependant	is_benefit_unit_non_dependant_for_legacy_benefits (not claimant/partner, not a Child Benefit child or QYP)

Consumers:

• is_lha_shared_accommodation_rate_specified_renter (UC) uses the UC test. That test excludes the renter's foster child (is_lha_foster_child, para 9(2)(c)), following Count other families' children and add the foster and overnight-care bedrooms in the LHA size criteria #2016's reading of "foster child" as a looked-after person under 18 placed with the renter (para 9(3) with the reg 2 foster parent definition). The WRA 2012 s.40 reading (a child is under 16) would instead count a looked-after 16- or 17-year-old who is not a qualifying young person as a non-dependant. The code records both readings. It also uses UC responsibility only for para 28(3) (is_responsible_for_child_or_qualifying_young_person_for_universal_credit), not the UC-or-HB blend, since HB has had its own category since Give sharers, boarders and lodgers their own rent, tenure and LHA category #2006.
• housing_benefit_LHA_category uses the HB test.

Other families' non-dependants:

• UC gives them to the household head's claim only (para 9(2)(f)), as uc_non_dep_deductions does.
• HB gives another family's non-dependant to every joint occupier (reg 3(1), (4); reg 74(5)). A joint occupier's own in-unit non-dependant, such as a joint tenant's adult son, is that occupier's only (LHA Guidance Manual para 2.093, example 2; HBGM A5 para 5.622). Both match Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017's housing_benefit_non_dep_deductions as of 155766b. A boarder or lodger has only their own family's (reg 3(2)(e)).

lha_renter_has_non_dependant is deleted. It was introduced in #1896 and has never been on main.

The 16-year-old rule

The blend excluded (age >= 16) & (age < 17) from non-dependants. No provision makes every 16-year-old a dependant for the whole year:

• UC reg 5(1)(a) makes a 16-year-old a qualifying young person "up to, but not including, the 1st September following their 16th birthday".
• For HB, the young person is the Child Benefit one (reg 19). Child Benefit (General) Regs 2006 reg 7 Case 1 keeps a school leaver a qualifying young person only until the week including the next terminal date (the last day of February, May, August or November). Reg 5 adds a 20-week extension for a 16-17-year-old registered with a careers service.

The annual model cannot place these dates. It does not need to for the shared rate:

• UC: a 16-year-old is either a qualifying young person the renter is responsible for, which fails para 28(3), or a non-dependant, which fails para 28(4).
• HB: they are either a young person in the claimant's family, so the claimant is a lone parent and not a "single claimant" or young individual (reg 2(1)), or a non-dependant (reg 3).

Either way there is no shared rate. Each test now uses the model's own young person definition. The one case where the rule mattered was wrong:

• HB's single-claimant test (is_single_person) uses the Child Benefit young person, which has no 16-year-old rule.
• So a 16-year-old outside the Child Benefit test was not a dependant there, and the rule also stopped them being a non-dependant.
• A young single claimant living with them therefore got the shared rate. Example: a parent aged 33 with a son of 16 who has left education got HB category A on the base and gets C here. UC gives C on both.

The same rule remains in is_responsible_for_child_or_young_person_for_uc_or_housing_benefit, now used only by the benefit cap. There the classification does change the rate, so it is left to a separate task.

Invariants

These hold for every input. All four are Hypothesis tests in test_lha_shared_rate_non_dependant_properties.py:

1. UC: a benefit-unit member aged 16 or over, other than the claimant or partner and not looked after by a local authority, always stops the renter being a specified renter.
2. HB: such a member who is not placed with the family (reg 21(3)) always stops the claimant being a young individual with no non-dependant.
3. Deduction implies non-dependant: any family charged a UC or HB non-dependant deduction has a non-dependant under that scheme's test. This is a differential check against the deduction formulas.
4. Agreement below 19: for a member under 19 who is not the claimant or partner, the UC and HB person-level definitions agree. They diverge from 19, when UC reg 5(1)(b) ends at the 1 September after the 19th birthday and Child Benefit reg 3(4) does not.

Mutation testing. Five mutants were tried:

• M1: the 16-year-old rule put back into HB;
• M2: UC drops in-unit non-dependants;
• M3: HB drops other families' non-dependants;
• M4: UC uses the legacy definition;
• M5: the specified renter ignores the UC non-dependant.

In round 1, M1, M3 and M4 survived: the generator rarely produced the deciding cases, and HB deductions are £0 at nil income. The properties now concentrate ages around 16-20 and give members and other families earnings. Explicit examples pin a 16-year-old school leaver, a 19-year-old in education and a shared house with earning non-dependants. In round 2, all five mutants are killed and the unmutated code passes.

Impact

These are real Microsimulation runs on the released enhanced FRS 2024-25 (sha256 03fe15e40a4c). Base is 94380e076 (#2017 at 155766b plus #2016 at 9311e4e); branch is ef6c77fbe. Figures are aggregates only, and any cell with fewer than 10 survey households is suppressed.

	2025	2026
Benefit units whose UC LHA category changes	0	0
Benefit units whose HB LHA category changes	0	0
UC specified renters switching on or off	0	0
UC, HB, household net income (BHC/AHC), poverty	unchanged	unchanged
Benefit units whose non-dependant flag changes (UC or HB)	fewer than 10 survey households (suppressed)	fewer than 10 survey households (suppressed)

The fix is a law cleanup with no measurable fiscal effect on the current data. The few 16-year-olds outside the young person test now count as non-dependants, and none was in a benefit unit where that moves a category.

Tests

• New LHA_shared_accommodation_non_dependants.yaml, 7 cases with each scheme's flag, responsibility and category:
  • a 16-year-old in education and one out of education;
  • a 19-year-old past the UC terminal date (a UC non-dependant but an HB young person);
  • a looked-after 17-year-old in education (a non-dependant under neither scheme), and one who has left education (a UC foster child but an HB non-dependant);
  • a foster child under 16;
  • a joint tenant's adult son (that tenant's non-dependant only, under both schemes).
• Existing lha_renter_has_non_dependant expectations are renamed to the two new outputs. UC and HB agree in every existing case.
• Full suites on ef6c77f:
  • YAML: 1,577 passed;
  • pytest: 2,072 passed, 45 skipped.
• Targeted: 98 YAML cases, plus 13 property tests (this PR's, Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017's and Count other families' children and add the foster and overnight-care bedrooms in the LHA size criteria #2016's bedroom properties).

Stack and coordination

• Base: in-unit-non-dep-deductions (Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017, head 155766b).
• Count other families' children and add the foster and overnight-care bedrooms in the LHA size criteria #2016 (lha-nondep-children-foster-rooms, head 9311e4e) is merged in as 94380e076, so the diff includes Count other families' children and add the foster and overnight-care bedrooms in the LHA size criteria #2016 until it lands.
• To see this PR's own changes only: 94380e0...lha-sar-non-dep-per-scheme
• Count other families' children and add the foster and overnight-care bedrooms in the LHA size criteria #2016's foster/adoption exclusion is preserved by construction. is_child_or_young_person_placed_with_family requires a Child Benefit child or QYP, and both new definitions already exclude those. The Count other families' children and add the foster and overnight-care bedrooms in the LHA size criteria #2016 session agreed.
• Count a non-dependant shared by joint tenants in each tenant's Housing Benefit size criteria #2029 (hb-joint-tenant-shared-non-dependant) also defines housing_benefit_claimant_has_non_dependant and owns which joint occupiers another family's non-dependant resides with, through an input. Whichever PR lands second composes the two: this PR's in-unit definitions, plus Count a non-dependant shared by joint tenants in each tenant's Housing Benefit size criteria #2029's non_dependants_residing_with in place of this PR's other-family term, with the UC variable named universal_credit_renter_has_non_dependant.
• When Count other families' children and add the foster and overnight-care bedrooms in the LHA size criteria #2016 and Charge non-dependant deductions for non-dependants within the claimant's benefit unit #2017 land on Give benefit-unit members aged 16 or over a bedroom in the LHA size criteria #2010, retarget this PR to lha-bedroom-young-people.

Related: #2014.

axiom:

• uksi/2013/376/schedule/4/paragraph/28: encoded-correct (companion tests renter_responsible_for_child_or_qualifying_young_person and non_dependant_in_relation_to_renter).
• UC Sch 4 para 9 and HB regs 3 and 13D(2)(a)(i): Encode the payer side for sharers, boarders and lodgers: UC Sch 4 paras 9 and 20, HB regs 3, 12B, 13D, 74 and Sch 1 meals, CTR joint liability (PE parity: policyengine-uk#2006) TheAxiomFoundation/rulespec-uk#406 queued (addendum with these cases).

🤖 Generated with Claude Code

[MaxGhenis]

Coordination note from #2016: #2016's head is now e5c36dc. Since 9311e4e it adds is_looked_after_child (the looked-after flag counts only under 18), which the UC, CTC and Pension Credit child tests and the placement test now use. It also replaces gov.dwp.LHA.foster_child_age_limit with household.demographic.looked_after_child_age_limit, and adds IS Sch 1B paras 2 and 2A. Please merge origin/lha-nondep-children-foster-rooms into this branch before it lands.

[MaxGhenis]

Coordination note from #2062 (issue #2059), which makes every programme read one household head.

This PR's LHA_additional_bedrooms, LHA_allowed_bedrooms, housing_benefit_LHA_additional_bedrooms and universal_credit_renter_has_non_dependant read the raw is_household_head input. That input can flag several members of a household, or none, and programmes reading it directly then disagree about whose household it is. #2062 adds is_resolved_household_head (exactly one per household) and defines benunit_contains_household_head from it.

Whichever of the two PRs lands second needs these readers switched:

• family level: benunit.any(person("is_household_head", period)) becomes benunit("benunit_contains_household_head", period), and person.benunit.any(person("is_household_head", period)) becomes person.benunit("benunit_contains_household_head", period);
• person level: person("is_household_head", period) becomes person("is_resolved_household_head", period).

#2062 adds a test, test_only_the_resolved_head_reads_the_flag, that fails while any module other than is_resolved_household_head reads the raw flag. If this PR lands first, #2062 makes the switch when it merges main. If #2062 lands first, the switch belongs here. Survey results do not change either way: the Enhanced FRS has exactly one flagged head per household.

[MaxGhenis]

Coordination with #2089 (each scheme its own benefit cap and LHA shared-accommodation rules), stacked on #2084.

For the LHA, #2089 adopts #2006's names and helpers, so this stack and #2089 meet on the same files:

• LHA_category stays the UC category. is_lha_shared_accommodation_rate_specified_renter is UC-only (Sch 4 paras 27-29). It now applies reg 3(3) directly: the claims_legacy_benefits stopgap is gone, and AFIP is in the para 29(5) list via UC reg 2's "attendance allowance".
• The HB side matches Give sharers, boarders and lodgers their own rent, tenure and LHA category #2006, with a minimal version of each file:
  • housing_benefit_LHA_category (reg 13D(2)(a)(i));
  • is_housing_benefit_young_individual (verbatim Give sharers, boarders and lodgers their own rent, tenure and LHA category #2006 base);
  • housing_benefit_severe_disability_premium_applies (Sch 3 para 14, with today's household-composition proxy outside the family);
  • housing_benefit_LHA_rate (verbatim);
  • LHA_cap reads housing_benefit_LHA_rate.
• The parameter gov.dwp.housing_benefit.severe_disability_premium.qualifying_benefits and lha_rate_for_category / category_maximum(..., category_variable) are verbatim Give sharers, boarders and lodgers their own rent, tenure and LHA category #2006.

#2089 keeps lha_renter_has_non_dependant for both schemes. Both shared-rate tests also read is_responsible_for_child_or_young_person_for_uc_or_housing_benefit: a dependant under one scheme only is the other scheme's non-dependant, which the proxy misses.

When this stack and #2089 meet, take this stack's versions of the HB LHA files: the (a)(ii) route, the non-dependant tests and the overnight-care and foster exceptions. Then:

• keep Give Universal Credit and Housing Benefit their own benefit cap and LHA shared-accommodation rules #2089's reg 3(3) lines in is_lha_shared_accommodation_rate_specified_renter: renter = is_claimant_or_partner & ~other_member_of_single_claim, and ~is_couple | uc_member_of_couple_claims_as_single_person;
• drop the union responsibility term in both tests once universal_credit_renter_has_non_dependant / housing_benefit_claimant_has_non_dependant replace the proxy.

#2006's housing_benefit_LHA_category already has no single-claim path for a couple, which is right for HB.