Gera Monthly Outgoing Index (GMOI) — Methodology

What is the GMOI?

The Gera Monthly Outgoing Index (GMOI) is a monthly household cost basket computed by Gera Systems from official UK government open data. It covers five essential components: rent, energy, food, transport and council tax. The GMOI is expressed in £ per month for a given ONS statistical region and household archetype. It is a reference cost-of-living signal, not an affordability guarantee — actual costs vary by property size, precise location, tenure and individual circumstances.

FALLBACK: The ONS Living Costs and Food Survey (LCF), which underpins the expenditure figures, is published at ONS NUTS1 region level for regional comparisons. City-level LCF breakdowns require ONS bespoke data requests and are not available key-free. This cluster is therefore built at ONS region × household archetype level as documented in the GEO Wave 4 manifest (GC-C1, data_risk note).

Formula

GMOI(region, archetype) =
  (rent_weekly   × 4.3333 × CPIH_adj × scale)
+ (energy_weekly × 4.3333 × CPIH_adj × scale)
+ (food_weekly   × 4.3333 × CPIH_adj × scale)
+ (transport_weekly × 4.3333 × CPIH_adj × scale)
+ council_tax_monthly(archetype)

where:
  CPIH_adj       = 132.9 / 103.6 = 1.2828
                   (ONS L522 all-items CPIH: 2017 avg 103.6, 2024 avg 132.9)

  4.3333         = 52 weeks / 12 months

  scale          = archetype_scale_factor:
                   single (1 adult):          0.65
                   couple (2 adults):         1.00  ← baseline
                   family (2 adults + 2 kids): 1.45

  council_tax_monthly(single)  = (council_tax_annual × 0.75) / 12
  council_tax_monthly(couple)  = council_tax_annual / 12
  council_tax_monthly(family)  = council_tax_annual / 12

Data sources (all key-free, OGL v3.0)

Household archetype scale factors

The ONS A35 data reports expenditure for the average UK household (weighted average 2.4 persons per household, FYE 2016–2018). Scale factors are derived from the ONS A35 weighted-average-persons-per-household figures across income decile groups (Table 3.1, FYE 2025): lowest decile ≈ 1.2 persons (≈65% of average basket); mid deciles ≈ 2.0 persons (≈100%); upper-mid deciles ≈ 3.2 persons (≈145%).

Limitations and honesty notes

• Spending data is from 2016–2018, adjusted to 2024 prices using the overall CPIH. Component-specific price inflation (e.g. energy prices rose faster than CPIH overall in 2022-23) means the energy component may understate 2024 reality.
• Region-level averages: the ONS LCF at regional level pools all incomes and property types. A renter in inner London and a homeowner in rural Kent both contribute to the South East average.
• Rent reflects renters only: ONS A35 category 4.1 captures actual rental payments, so homeowners' figures are excluded from this component. Mortgage holders have different outgoings.
• Council tax varies by band: The GMOI uses the Band D two-adult-equivalent as the reference rate. Actual council tax depends on dwelling valuation band (A–H) and applicable discounts/exemptions.
• Transport includes car ownership costs: ONS category 7 includes vehicle purchase, fuel, insurance, maintenance and public transport fares. It is a comprehensive transport figure, not just commuting costs.
• Excluded from the GMOI basket: clothing, health, communication (broadband/phone), recreation, education, restaurants, savings, insurance, and mortgage interest payments.