[MaxGhenis]

Fixes #2014

Reproducer: policyengine_uk/tests/policy/baseline/finance/benefit/family/benefit_unit_non_dependants.yaml::UC, an adult son in the renter's benefit unit bears a housing cost contribution; policyengine_uk/tests/test_benefit_unit_non_dependant_properties.py::test_deductions_match_the_oracle

Stacked on #2007 (base hb-ctr-non-dep-exemptions), which is on main. Retarget to main once #2007 merges.

Until 2026-10-20 this PR was stacked on #2010 (lha-bedroom-young-people). #2010 has not moved since 2026-10-02, and this PR needs nothing of it: #2010 changes only the LHA size criteria. Merge commit 7f9ef1a merged main and #2007 into this branch and put #2010's own files back to main's versions. The one cross-PR invariant, that an in-unit non-dependant has a bedroom, moved to #2010 (comment).

Merge order

This PR needs #2007's HB and CTR claimant exemptions: HB reg 74(6), SPC reg 55(6) and CTR Sch 1 para 8(6) (review r2, F2). Without them, a blind claimant, or one receiving AA, the DLA care component, the PIP daily living component or AFIP, would newly lose HB and CTR for an adult son. Stacking on #2007's branch enforces the order: this PR cannot reach main before #2007 does. It lands on the PE-UK merge-on-gates rule (d822) when:

• Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007 is merged;
• this PR is retargeted to main;
• CI is green on its head;
• an independent review approves that head.

Problem

A benefit unit can include someone aged 16 or over who is neither the claimant or partner nor a child or young person the claimant is responsible for. Examples are an adult son, or a 19-year-old who has left education. In law that person is a non-dependant of the renter. The model treated them inconsistently:

• lha_renter_has_non_dependant already counted them.
• No deduction was ever charged for them:
  • uc_non_dep_deductions and housing_benefit_non_dep_deductions counted only people in other families (is_non_dependant_of_household_head). The individual eligibility variables also excluded anyone in a family liable for rent.
  • council_tax_reduction_non_dep_deductions subtracted the claimant's own benefit unit.

So a lone parent on UC with a 25-year-old son paid no housing cost contribution. The same son in his own benefit unit in the same household cost the parent £96.55 a month.

The UC renter exemption (Sch 4 para 15) was also missing. When the renter or either joint renter is blind or receives AA, the middle or highest DLA care component, or the PIP daily living component, no contribution should be made for any non-dependant.

The law

Fetched from legislation.gov.uk on 2026-10-01 (texts in the review folder's law/).

• UC, Sch 4 para 9:

  • (1) "the members of a renter's extended benefit unit are— (a) the renter (or joint renters); (b) any child or qualifying young person for whom the renter or either joint renter is responsible; and (c) any person who is a non-dependant."
  • (2) "A person is a non-dependant if the person normally lives in the accommodation with the renter (or joint renters) and is none of the following— (a) a person within sub-paragraph (1)(a) or (b); … (f) a person who has already been treated as a non-dependant in relation to a claim for universal credit by another person liable to make relevant payments …; (g) a child or qualifying young person for whom no-one in the renter's extended benefit unit is responsible."
  • Para 13(1): "a deduction is to be made in respect of each non-dependant who is a member of the renter's extended benefit unit".
  • Para 15 exempts "any renter who is a single person", or "any joint renter where at least one joint renter is a person", to whom (2) applies. Joint renters are joint claimants (para 1(2)).
  • Para 16 exempts the non-dependant, including "(a) a person who is under 21 years old" and "(b) a person in receipt of state pension credit".

• HB, HB Regs 2006 / HB (SPC) Regs 2006 reg 3:

  • (1): "'non-dependant' means any person, except someone to whom paragraph (2) applies, who normally resides with a claimant or with whom a claimant normally resides".
  • (2) excludes:
    • "(a) any member of the claimant's family";
    • "(c) a child or young person … not a member of his household by virtue of regulation 21";
    • "(d) … [a person] liable with the claimant … to make payments in respect of his occupation of the dwelling";
    • "(e)(i) any person who is liable to make payments on a commercial basis to the claimant or the claimant's partner".
  • (4): "a person resides with another only if they share any accommodation except a bathroom, a lavatory or a communal area within the meaning prescribed in paragraph 8 of Schedule 1 but not if each person is separately liable to make payments in respect of his occupation of the dwelling to the landlord".
  • The family is the couple and their children and young persons. A young person is a Child Benefit qualifying young person (reg 19).
  • Reg 74 / SPC reg 55 deduct for a non-dependant "aged 18 or over". Under (5): "Where a person is a non-dependant in respect of more than one joint occupier of a dwelling … the deduction … shall be apportioned between the joint occupiers … having regard to the number of joint occupiers and the proportion of the payments in respect of the dwelling payable by each of them."

• CTR:

  • Definitions: SI 2012/2885 reg 9 (the same definition; family in reg 6); WSI 2013/3029 reg 9; SSI 2021/249 reg 8; SSI 2012/319 reg 3.
  • Reg 9(2)(e) excludes "any person who is liable to make payments on a commercial basis to the applicant or the applicant's partner".
  • Deductions are for non-dependants "aged 18 or over" (Sch 1 para 8 and equivalents).
  • Under para 8(5)(c), one who "is a non-dependant of two or more of the liable persons" is "apportioned equally between those liable persons".

• CTR applicant (#2078): where a liable household head is not her benefit unit's claimant or partner, she applies alone (council_tax_reduction_head_applies_alone), and is_council_tax_reduction_applicant_or_partner is her alone. The benefit unit's couple are then outside her family under reg 9(2)(a).

Change

	Before (main + #2007)	After
Who	only members of other families who are not liable for rent	also benefit-unit members who are neither the claimant/partner nor that scheme's child or young person: • is_benefit_unit_non_dependant_for_universal_credit: 16+, not a UC qualifying young person (para 9(1)-(2)(a), (g)); • is_benefit_unit_non_dependant_for_legacy_benefits for HB: not a Child Benefit child or QYP (reg 3(2)(a), (c)); • new is_benefit_unit_non_dependant_for_council_tax_reduction for CTR: not the CTR applicant or partner (#2078's identity) and not a Child Benefit child or QYP (reg 9(2)(a), (c))
UC	other families' non-dependants count in one claim, uc_non_dependants_counted (para 9(2)(f))	unchanged for other families. A family's own in-unit non-dependant counts in its own claim if that family is renting and claims UC, and otherwise in the counted claim. New para 15 exemption, uc_non_dep_deductions_renter_exempt. The para 16(2)(b) Pension Credit limb applies only to the claimant or partner, who receive it, so a pensioner's adult son is not exempt by her award.
HB	#2007's per-couple amounts for other families, apportioned by rent share; none under the claimant exemption	every non-dependant, in any family, pooled through #2007's deduction_per_family (one deduction per couple, the higher; each other adult separately) and apportioned between the joint occupiers by rent share (reg 74(5)). That includes a joint occupier's own adult son and a boarder's or lodger's. A boarder or lodger is not a joint occupier with the householder, so it also bears its own in-unit non-dependant in full. #2007's claimant exemption still zeroes the claim, and HB eligibility keeps #2007's individual exemptions.
National CTR	#2007's two schemes (the head's family's and the other), other families' amounts per scheme, joint-liability share, the per-applicant exemption	in each scheme, every non-dependant is pooled, a lodger's included. The applicant's own family members are left out (reg 9(2)(a)) and its in-unit non-dependants kept, each couple once. The result is apportioned by joint-liability share (para 8(5)) and charged to claiming families only. The per-applicant exemption still zeroes the claim.
Local CTR (5 English schemes)	other families' non-dependants	unchanged: the local aggregation is masked to the same other-family term as the eligibility

Joint occupiers and lodgers

A joint occupier's adult son normally resides with every joint occupier he shares accommodation with (HB reg 3(1), (4); CTR reg 9(1)). None of reg 3(2)(a)-(f) excludes him in relation to the other occupier, so he is a non-dependant of each, apportioned by reg 74(5) or para 8(5). That is how the model already treats a non-dependant in another family. So for joint occupiers (HB and CTR), and for CTR generally, the result does not depend on whether the survey codes the son in his parent's benefit unit or in his own: two YAML cases check the two codings give the same deductions. The exceptions are listed under "Not modelled".

Reg 3(2)(e)(i) and CTR reg 9(2)(e) exclude only the person liable to pay the claimant. The household extension in (e)(iii) is for the landlord's side. So a lodger's adult son who pays nothing himself is the householder's non-dependant. For HB he is also the lodger's own.

An earlier head (155766b) charged a joint occupier's own son wholly to that occupier, citing LHA Guidance Manual 2.093 example 2 and HBGM A5 5.622. Review r2 (F3) showed neither supports that:

• the LHA example is about the size criteria, and concerns a sister, who in the model is another family's non-dependant and is apportioned;
• 5.622 is conditional ("If a person is a non-dependant of only one of the joint occupiers").

2d54628 follows the text.

CTR: a head applying alone

Where a liable household head is not her benefit unit's claimant or partner, she applies alone (#2078). Her benefit unit's couple are then outside her family and are her non-dependants (reg 9(1), (2)(a)). As a couple they pay one deduction, the higher (Sch 1 para 8(3)), or one for each member in the Welsh working-age scheme where the couple has a UC award (WSI 2013/3029 Sch 6 para 5(3)).

For UC and HB the couple stay the benefit unit's claimant and partner. The head is the householder in whose name the accommodation is rented, so she is no one's non-dependant (UC Sch 4 para 9(2)(d); HB reg 3(2)(d)-(e)). Both in-unit helpers exclude is_resolved_household_head. YAML cases pin both sides (review r4, F1).

Local schemes

Merton, Kingston, Newham, Westminster and Oxford keep their own aggregation (_legacy.local_non_dep_deductions). The shared eligibility now also covers in-unit non-dependants, so the local aggregation masks the individual deductions to in_other_non_liable_family. The eligibility uses the same function: #2007's claimant-family test (outside every claiming, sharing or lodging family). The local schemes are therefore exactly as on #2007's base. #2077 (stacked on this PR) replaces the mask with each scheme's pooled aggregation.

Other compositions

• Give Council Tax Reduction to the household head's family, not the oldest adult's #2009, Assess each Council Tax Reduction claim under its own family's scheme and exemption #2015, Means-test the Council Tax Reduction applicant and partner, not the benefit unit's claimant #2078 (CTR claimant, per-family scheme and exemption, applicant identity) are on main and composed here: the claimant-family term, Assess each Council Tax Reduction claim under its own family's scheme and exemption #2015's council_tax_reduction_applicant_has_non_dep_exemption and Means-test the Council Tax Reduction applicant and partner, not the benefit unit's claimant #2078's applicant identity.
• Count a non-dependant shared by joint tenants in each tenant's Housing Benefit size criteria #2035 (shared non-dependants in each joint tenant's HB size criteria): whichever of Count a non-dependant shared by joint tenants in each tenant's Housing Benefit size criteria #2035 and this PR lands second also counts a joint occupier's in-unit non-dependants in every other joint occupier's HB size criteria, through housing_benefit_other_occupiers. The YAML case for that: a joint tenant's son aged 17 not in education gives the other tenant 2 bedrooms.
• Apply each scheme's own non-dependant test to the LHA shared accommodation rate #2030 and Charge in-unit non-dependants in the local Council Tax Reduction schemes #2077 are stacked on this PR's branch and were told to merge 7f9ef1a.

Invariants (stated and tested)

Hypothesis properties are in test_benefit_unit_non_dependant_properties.py. They are derandomized, with 10 examples each, on populations of up to 5 households. The populations include sharers, lodgers, non-dependant families, adult children, qualifying young persons (including looked-after ones), pensioner heads with working-age sharers, and exemption flags.

1. Oracle (differential). A plain-Python calculation from the generated structure must match each family's UC, HB and CTR deductions, and who is eligible for an individual HB or CTR deduction.
   • It decides who is whose non-dependant, couples once, HB rent shares, lodgers' own in full, the applicant's own family left out, and the claimant exemptions.
   • It reads from the model: the individual amounts; which UC claim counts the household's non-dependants and whether a family claims UC; the CTR claim flags, joint-liability shares and each family's scheme. Other-scheme amounts come from the aggregator's own helper.
   • It checks that the members each scheme classes as in-unit non-dependants (UC, HB and CTR sets) are exactly the generated non-QYP members.
2. Conservation.
   • HB deductions (a couple's once) are borne in full across the joint occupiers, plus once more by a lodger for its own non-dependant, where no claimant is exempt.
   • CTR deductions are borne by each claiming family, under its own scheme, in proportion to its joint-liability share (Give sharers, boarders and lodgers their own rent, tenure and LHA category #2006's per-person shares need not sum to one); none where the applicant is exempt. This holds on the generator's domain (rent > 0, claimants liable).
   • Each UC contribution is borne by at most one family.
3. Exemptions.
   • A para 15-exempt family has no UC deductions.
   • No deduction is made for anyone under 21 (UC) or under 18 (HB, CTR).
   • No one in a rent-liable family is charged other than its in-unit non-dependants.
4. No-op. Where no benefit unit contains a non-dependant, every family's deductions equal Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007's formulas with this PR's para 15 exemption and claim flag: UC through the counted claim, HB by rent share, and CTR per scheme by claim share, each with the exemptions.

Tests

• benefit_unit_non_dependants.yaml: 41 cases at the regulations' 2026-27 amounts (UC £96.55 a month; HB £20.40, £64.35 and £105.20 a week).
  • UC: adult son; under 21; responsible QYP; looked-after QYP; renter on PIP; blind partner; a disabled child does not exempt the renter; son on AA; the family's PC; own plus other-family non-dependants; a non-dependant family's own adult; a sharer's own; housing element net of the contribution; a non-claiming head's son counted in the sharer's claim; a pensioner's Pension Credit not exempting her adult son.
  • HB: part-time son; £300-a-week daughter; under 18; Child Benefit young person; joint tenants share one tenant's son by rent share, with the same result when he is coded as his own unit; a lodger's son is the lodger's and the householder's; a blind sharer's son still half the head's; an exempt lodger's son still the householder's.
  • CTR: own family; under 18; jointly liable applicants share one's son equally; another family's adult, shared; a lodger's son is the householder's; non-claiming families bear nothing; an applicant is never charged for itself; a blind head or sharer exempts only its own claim; a head applying alone is charged once for her benefit unit's couple.
  • Composition cases with Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007: zero income, students, a parent's IS, a non-dependant couple with an adult son, England pensioner scales.
  • Local CTR (Newham): a jointly liable sharer does not bear the head's son.
• Updated eligibility YAMLs. A lone person in a single-person household is not anyone's non-dependant, so these tests state who the person is a non-dependant of. A 19-year-old on UC with no earnings is exempt under reg 74(8)(b), so the in-unit eligibility case uses a 30-year-old.
• On 7f9ef1a (ae4e42b changes only the property oracle; 89beee8, 49bd8c3 and fa62f98 merge Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007's later heads; 58db77c adds the review r4 fixes):
  • policyengine-core test on finance/benefit/family, gov/local_authorities and consumption: 1,632 passed;
  • non-dependant property suites: 14 passed. One Give sharers, boarders and lodgers their own rent, tenure and LHA category #2006-era property, test_rent_of_sharers_boarders_and_lodgers_properties.py::test_non_dependants, fails on Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007's own base 0b6c3db too. Its HB conservation check predates Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007's claimant exemption, which zeroes an exempt joint occupier's share. Fixed in Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007 at 8e60349, merged here as 89beee8: 6/6 pass. Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007's next head (2574473, merged as 49bd8c3) adds a mixed-scheme CTR YAML file, and two of its cases fail on Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007's own head as well; that is reported to Apply Housing Benefit and national Council Tax Reduction non-dependant deductions as legislated #2007's owner. Otherwise the targeted YAML passes: 1,638..
• Earlier rounds (old stack): full suites 1,539/1,627 YAML and 2,051/2,073 pytest passed; mutation v3 YAML killed 18/19, properties 17/19, with the one survivor then pinned by a YAML case. Review r4 reruns mutation on this head.

Impact (real microsimulation)

These figures come from the released enhanced FRS 2024-25 in uk-data 1.58.1 (HF snapshot 2526edbb, sha256 056e80fd…). The base is #2007 at 0b6c3db, this PR's base; the branch is 89beee8 (same model code as ae4e42b). Each figure comes from a real run of the full model. A survey household is counted by its rent and members' ages, and any cell from fewer than 10 survey households is suppressed.

Effects, £m a year:

Year	UC paid	HB	CTR awards	Household net income	Households gaining
2025	+57.5	0	<10 households	+57.5	35k (43 survey households)
2026	+59.9	0	<10 households	+59.9	35k (43)
2027	+59.0	0	<10 households	+58.9	33k (42)
2028	+60.4	0	<10 households	+60.4	33k (42)
2029	+61.9	0	<10 households	+61.8	33k (42)
2030	+63.4	0	<10 households	+63.4	33k (42)

No household loses. Poverty before and after housing costs changes for people in fewer than 10 survey households (suppressed).

Where it comes from (2026). Rerunning the branch with only uc_non_dep_deductions_renter_exempt (para 15) switched off changes no award. So the in-unit charge, the UC routing and the Pension Credit gate move nothing on the survey, and the whole UC effect is the para 15 renter exemption:

• 42k benefit units (53 survey households) lose £71.0m of UC non-dependant deductions;
• their housing costs element rises by £61.0m for 35k (43 survey households);
• UC paid rises by £59.9m.

The in-unit group itself is 23k people (20 survey households): 18k aged 16-17 (12 survey households), 18-20 suppressed, none 21 or over. UC exempts everyone under 21 (para 16(2)(a)), and HB and CTR deductions change for fewer than 10 survey households.

Intermediate variables. council_tax_reduction_non_dep_deductions falls by £232.8m across 234k benefit units because non-claiming families now read zero (only claiming families bear deductions). The individual UC and HB deduction variables fall by tens of £bn because they now read zero for people who are nobody's non-dependant. No award changes through these.

The earlier figure (UC +£39.1m in 2026, old stack, uk-data 1.57.4) is superseded. Both the model's base and the data have changed since then (for example, main added the single-claim rule uc_non_dependants_counted, and uk-data moved to 1.58.1). The difference between the two figures was not decomposed.

Review

• Review r1 (Opus 5.5) was lost to a session limit. Its counterexamples were folded in at 155766b.
• Review r2 (Opus 5.5) on 155766b: F1-F5 (per-applicant CTR exemption, merge order, joint-occupier pooling, lodger's son, local neutrality), all fixed.
• Review r3 (Opus 5.5) on e72f2b8: F1-F5 confirmed fixed, local schemes exactly neutral; R3-1 to R3-11 fixed or disclosed.
• Review r4 (Opus 5.5, Subfleet 20261020-191444-in-unit-nondep-review-r4) on ae4e42b:
  • F1: a head applying for CTR alone was charged as her benefit unit's UC and HB non-dependant. Fixed: the household head is excluded from both in-unit helpers.
  • F2: the claim flag decides routing. Disclosed, with a YAML case.
  • F3: Reproducer line. Added.
  • F4: an in-unit parent of a child under 5. Disclosed.
  • F5: wording nits. Fixed.
  • Fixes are at 58db77c. The verdict is pending while r4 runs its mutation checks.

Not modelled / follow-ups

• A boarder's or lodger's adult relative coded in his own benefit unit is charged to the householder only. Coded in the lodger's unit, he is charged to both, as reg 3(2)(e)(i) and (iii) give. The model cannot tell which separately coded adult is the lodger's. (The householder's own household is rightly not the lodger's non-dependant: reg 3(2)(e)(iii); UC Sch 4 para 9(2)(e).)
• An in-unit non-dependant's own benefits are not modelled (receives_benefits_in_own_right does not say which benefit). So the exemptions for a non-dependant on IS, income-based JSA or income-related ESA, or on UC with no earned income (HB reg 74(8), CTR Sch 1 para 8(8), SSI 2021/249 reg 90), never apply to them. The same son coded as his own benefit unit gets his own UC award and can be exempt. This sits inside a suppressed survey cell.
• "Makes a UC claim" is the model's would-claim flag for a renting, UC-eligible family (claims_universal_credit), as in main's uc_non_dependants_counted. So a family flagged as claiming counts its own in-unit non-dependants even where its award is nil, though in law a family with no claim treats no one as its non-dependant (para 9(2)(f)). A family flagged as not claiming, which the survey's take-up draws produce, passes them to the counted claim, and a YAML case pins that. Real entitlement cannot be the test without a branch calculation, because UC entitlement depends on these deductions (review r4, F2).
• An in-unit parent of a child under 5 in the same benefit unit is charged a UC contribution. Para 16(2)(i) exempts a non-dependant responsible for a child under 5, but the model gives responsibility for the benefit unit's children to its claimant or partner, and UC reg 4(4) gives a child to one person only (review r4, F4).
• Two in-unit non-dependants who are a couple (neither the benefit unit's claimant nor partner) pay two HB deductions, not one on their joint income (reg 74(3)-(4)). The model has no relationship data to pair them. The FRS gives every couple its own benefit unit, so this arises only in user-entered households. For CTR, the couple in a head-applies-alone family is charged once (both members in the Welsh working-age scheme with a UC award).
• A joint occupier's or lodger's young person aged 18-19. Read literally, they are the other occupier's non-dependant, since they are not in that occupier's family. The model treats them as no one's.
• Inherited from Give sharers, boarders and lodgers their own rent, tenure and LHA category #2006:
  • per-person joint-liability shares, so for a couple jointly liable with a single sharer, part of each pooled CTR deduction is charged to no one;
  • FRS sharers with their own agreement are apportioned as joint occupiers, although reg 3(4)'s tail and reg 74(5) would charge each claim in full.
• Local English CTR schemes: Charge in-unit non-dependants in the local Council Tax Reduction schemes #2077.

axiom: UC Sch 4 para 13 encoded-correct; TheAxiomFoundation/rulespec-uk#413 queued (UC Sch 4 paras 15-16); TheAxiomFoundation/rulespec-uk#406 queued (UC Sch 4 para 9, HB reg 3, CTR reg 9: who is a non-dependant, joint occupiers, lodgers, the household head); TheAxiomFoundation/rulespec-uk#407 queued (HB reg 74, SPC reg 55, CTR Sch 1 para 8)

🤖 Generated with Claude Code

[MaxGhenis]

Composition note from #2078 (stacked on #2009), which makes the CTR means test assess the applicant and partner rather than the benefit unit's claimant and partner.

#2078 adds is_council_tax_reduction_applicant_or_partner (Person) and council_tax_reduction_head_applies_alone (BenUnit). Where the household head is liable but is not the benefit unit's claimant or partner, the head applies alone, and the benefit unit's claimant and partner are not her family. An example is a grandmother head sharing a benefit unit with a young couple and their baby.

For CTR, a family's in-unit non-dependants should then be benefit-unit members aged 18 or over who are neither is_council_tax_reduction_applicant_or_partner nor a child or young person of the applicant's family. Here is_benefit_unit_non_dependant_for_legacy_benefits uses is_claimant_or_partner. Composed with #2009/#2078, that would make the grandmother a non-dependant in her own claim and the young couple not hers, the reverse of the law (SI 2012/2885 reg 9(1), (2)(a)). HB can keep the generic identity; the CTR deduction (council_tax_reduction_individual_non_dep_deduction_eligible, council_tax_reduction_non_dep_deductions) needs the CTR one.

This matters more after #2078: for a head who applies alone, #2078 stops counting the young couple's income, as the law requires, and leaves their non-dependant deduction (when they are 18 or over) to this PR.