Gera True Monthly Outgoing (GTMO) — Methodology

1. The four inputs

All four inputs are published under the Open Government Licence v3.0 and are freely available without a data-sharing agreement or API key.

2. Regional utility and transport costs

The ONS Family Spending survey publishes household expenditure at the ONS English region level (9 regions), not per local authority. Every local authority in the cluster inherits the utility and transport costs published for its ONS region. This is stated on every area page. Per-LA commute-fare tables are not freely available at this coverage without a data-sharing agreement — the cluster uses the ONS regional transport figure as the documented ONS-NTS-based fallback (brief: "use ONS NTS average travel cost if per-LA fare lookup unavailable; never fabricate").

Weekly figures converted to monthly by multiplying by 52 then dividing by 12.

Source: ONS Family Spending in the UK, Workbook 3 (expenditure by region), FYE 2025 (3-year average FYE 2023-2025). OGL v3.0.

3. GTMO formula

GTMO = rent + ctMonthly + utilMonthly + transportMonthly

Where:
  rent             = ONS PRMS average monthly private rent (per LA, all bedrooms)
  ctMonthly        = MHCLG Band D council tax / 12 (per billing authority)
  utilMonthly      = ONS Family Spending electricity+gas+other fuels × 52/12 (per region)
  transportMonthly = ONS Family Spending transport category × 52/12 (per region)

4. GDIR formula and income derivation

GDIR = (netMonthly - GTMO) / netMonthly × 100

netMonthly = (grossAnnual - incomeTax - nationalInsurance) / 12

Income Tax (England/Wales/NI, 2026-27):
  Personal allowance:    £12,570   0%
  Basic rate band:       £12,571 – £50,270  20%
  Higher rate band:      £50,271 – £125,140 40%
  Additional rate:       > £125,140          45%

National Insurance (Class 1 employee, 2024-25 rates):
  Below primary threshold (£12,570):  0%
  Primary threshold to UEL (£50,270): 8%
  Above UEL:                          2%

Illustrative net monthly incomes:
  £25,000/yr gross → £1,793.3/mo net
  £35,000/yr gross → £2,393.3/mo net
  £45,000/yr gross → £2,993.3/mo net

HMRC source: https://www.gov.uk/income-tax-rates. NI rates carried forward from 2024-25; no change announced for 2026-27 at time of computation.

5. Coverage and exclusions

The cluster covers 294 English local authorities for which all four inputs are present at a 1:1 local-authority granularity:

• ONS PRMS publishes average monthly rents per local authority — the join is direct.
• MHCLG council tax is published per billing authority — the join is direct on the ONS/GSS area code.
• ONS Family Spending utility and transport costs apply at the nine ONS English region level. Each local authority inherits its region's figure. This is the finest granularity in the published data.
• Scotland, Wales and Northern Ireland are excluded: ONS PRMS provides UK-wide rent data but council tax and utility/transport benchmarks in this cluster use England-specific MHCLG and ONS Family Spending sources. Separate clusters would be needed for devolved nations.
• An area is only included when all four source values are present. No missing value is treated as zero.

6. Worked example — Hartlepool (rank #1)

• Rent: £561/mo (ONS PRMS May 2026, area code E06000001)
• Council tax: £2,560/yr = £213/mo (MHCLG 2026-27, Band D)
• Utilities (North East): £159/mo (ONS Family Spending FYE 2025, row 4.4)
• Transport (North East): £299/mo (ONS Family Spending FYE 2025, row 7)

GTMO = 561 + 213.35 + 159.03 + 299
     = £1,232.38/mo

At £35,000/yr gross (net £2,393.3/mo):
  GDIR = (2393.3 − 1232.38) / 2393.3 × 100
       = 48.5%    (rank #1 of 294)

7. Limitations and interpretive notes

• Council tax uses Band D as the representative benchmark. Actual bills depend on property band (Bands A–H carry different multipliers) and any discounts (single-occupier 25% discount, council-tax support schemes).
• Utility and transport figures are regional averages (9 ONS regions). Actual household expenditure varies by property size, energy efficiency, travel habits and lifestyle.
• Rent is the ONS average for all property sizes in the area. Actual rent depends on property type and bedroom count.
• Transport uses ONS Family Spending category 7 (all household transport spend — car, public transport, etc.) as the regional proxy. Per-route commute costs for a specific workplace are not included because no per-LA commute-fare table is freely available at this coverage.
• GDIR is a simple ratio of remaining income; it does not account for food, childcare, debt repayments or other personal expenditure. It is a starting point for affordability comparison, not a personal financial plan.
• Re-computed quarterly as the ONS PRMS and MHCLG council tax tables update; each page carries the as-of date.