Rent vs buy evidence, open to inspection.
Rules, dates and evidence should be inspectable. HMRC remains authoritative for tax; historical data remains evidence, not a forecast. Open Growth and returns below the calculator to choose historical evidence. The compact layout uses the same source data, tax rules and assumptions documented here.
Last full source review · 2 September 2026
Employment, pension and childcare rules have their own working-days source register, separate from the housing evidence below.
SOURCE 01
Tax rules
Stamp Duty Land Tax
The calculator’s residential SDLT logic is limited to England and Northern Ireland. The current bands below took effect on 1 April 2025 and were checked against GOV.UK on 2 September 2026. HMRC’s calculation manual requires the final marginal tax amount to be rounded down to the nearest whole pound; the model applies that rule after summing the bands.
| Portion of price | Standard rate | Additional property |
|---|---|---|
| Up to £125,000 | 0% | 5% |
| £125,001–£250,000 | 2% | 7% |
| £250,001–£925,000 | 5% | 10% |
| £925,001–£1.5m | 10% | 15% |
| Above £1.5m | 12% | 17% |
First-time buyers
Qualifying purchases pay 0% up to £300,000 and 5% on the portion from £300,001 to £500,000. Above £500,000, the relief is unavailable and standard rates apply.
Additional property
The model applies the additional-property rates from £40,000 and returns £0 below that threshold. From £40,000, it adds five percentage points to the standard bands. Whether the higher rates legally apply depends on the buyer and transaction.
SOURCE 02
Market evidence
UK House Price Index
The property-growth chooser uses the June 2026 UK House Price Index. It covers completed sales, includes cash and mortgage purchases, and supports English local-authority and property-type histories. Northern Ireland is available at national level only in this source.
- Producer
- HM Land Registry with LPSNI, ONS and Registers of Scotland
- Release
- June 2026 · published 19 August 2026
- Evidence endpoint
- June 2025 · latest 12 months excluded
- Coverage
- 295 English local authorities, 9 regions and Northern Ireland nationally
Required attribution
Contains HM Land Registry data © Crown copyright and database right 2020. This data is licensed under the Open Government Licence v3.0.
Inflation evidence
ONS CPIH all-items index
Historical inflation uses the monthly CPIH all-items index, series L522 from ONS dataset MM23. The series used here covers January 1988 to May 2026, from the release published 17 June 2026. Property, rent and referenced investment comparisons match CPIH to their own historical start and end months; no future value is inferred from this series. CPIH is a broad UK purchasing-power measure, not wage growth, housing affordability or a household’s personal inflation rate.
Source: Office for National Statistics, Consumer price inflation time series (MM23), CPIH all-items index (L522). Contains public sector information licensed under the Open Government Licence v3.0.
Historical growth is not a forecast. The app calculates nominal compound annual change and change after matched CPIH over the selected 5, 10, 15 or 20-year period. A historical rate is applied only when “Use” is selected. “Inflation & history” reveals the matched CPIH and after-inflation context; “Sources & method” contains provenance and attribution. The same disclosures are used in the rent and investment choosers. Source data, transformations and model assumptions are unchanged. The latest year is excluded because lower-geography estimates can be revised as more registered sales arrive. Editing the applied percentage manually removes its evidence label.
English local authorities are connected to regional benchmarks using the Office for National Statistics LAD25-to-region lookup, retrieved 12 July 2026. Source: Office for National Statistics licensed under the Open Government Licence v.3.0.
SOURCE 03
Rental evidence
ONS Price Index of Private Rents
The rent-growth chooser uses the ONS Price Index of Private Rents release published 19 August 2026. For England, PIPR aims to track the whole private rental stock rather than only the latest listings. The release publishes indices and modelled monthly rent levels by geography and rental segment; Northern Ireland uses a different observation basis, explained below.
- Producer
- Office for National Statistics
- Release
- 19 August 2026 · retrieved 2 September 2026
- Evidence endpoint
- May 2026 · latest two months excluded
- Coverage
- 294 English local authorities and 8 Northern Ireland rental areas
Required attribution
Source: Office for National Statistics licensed under the Open Government Licence v3.0. Crown copyright © 2026.
Whole market
An all-private-rents index and modelled monthly rent level.
Bedrooms
Separate one, two, three and four-or-more-bedroom histories.
Property type
Detached, semi-detached, terraced and flat or maisonette histories.
The app annualises the change in the unrounded PIPR index over the selected five- or ten-year period. Published rent levels are rounded and are shown only as context. Every geography uses May 2026 as a common endpoint: the August workbook continues to July for England, but Northern Ireland source observations arrive two months later. This avoids applying imputed Northern Ireland values or comparing areas over different end dates.
England local-authority data use achieved rents from new and existing tenancies. Northern Ireland is published through eight Broad Rental Market Areas and uses advertised new lets. The chooser states that difference beside every result. English local results are shown with their regional benchmark; Northern Ireland results are shown with the national benchmark. ONS advises using longer local trends because lower-geography collection volumes can produce volatility. The City of London and Isles of Scilly are not published because of low collection volumes.
Nominal index growth enters the nominal model. CPIH is matched to the exact start and end months, while the calculated after-CPIH change remains read-only purchasing-power context. Editing the applied rent-growth percentage manually removes the evidence label.
SOURCE 04
Investment references
Historical investment references
The investment return remains a visible, editable nominal model assumption. The historical chooser applies a nominal GBP rate and shows after-CPIH context calculated from actual before-tax net asset value (NAV) total returns for two representative funds disclosed in pinned SEC filings: Vanguard Total World Stock ETF (VT) for global equities and State Street SPDR S&P 500 ETF Trust (SPY) for US large caps. These fund histories include their ongoing expenses.
Observed
A quote, listing, statement or published rule with a date.
Derived
A transparent calculation from a named public dataset.
Assumed
A value chosen to test a possible future scenario.
Global equities proxy — VT
Vanguard Total World Stock Index Fund ETF Shares. The 2026 filing supplies 5- and 10-year NAV returns to December 2025; the 2016 filing supplies the earlier 5-year factor used for 15 years.
US large-cap proxy — SPY
State Street SPDR S&P 500 ETF Trust. The 2026 and 2016 filings provide exact, non-overlapping before-tax fund-return factors for 5, 10, 15 and 20 years.
GBP conversion — DEXUSUK
Federal Reserve H.10 daily US dollars per pound sterling. Each window uses the endpoint observation, or the nearest prior published observation when 31 December is not available.
Each disclosed annualised USD return is converted back to a total factor. Longer windows multiply exact, non-overlapping factors rather than average percentages. The app then calculates GBP factor = USD fund factor × (USD/GBP at start ÷ USD/GBP at end), annualises that factor, and compares it with ONS CPIH over the same December-to-December window. The after-CPIH rate divides compounded factors rather than subtracting annual percentages. It is shown as context; the nominal GBP history is passed unchanged to the nominal cash-flow model.
The GBP results are unhedged equivalents, not GBP share-class returns. Fund expenses are reflected; UK platform charges, trading costs and tax are excluded. Historical performance is not a forecast, and no affiliation with or endorsement by the SEC, Federal Reserve, Vanguard, State Street or a benchmark provider is implied.
INTERFACE NOTE
Browser · API · MCP
The source register travels with the model.
The JSON API and MCP tool use the same bundled tax logic, evidence transformations and model defaults as the browser. They do not introduce a live market feed, a separate forecast or agent-generated assumptions.
Machine responses include the model version, supported jurisdiction, SDLT effective date, effective inputs, substituted defaults and links back to this register. The caller should preserve those fields when a result is quoted or cached and re-check this page when tax-rule currency is material.
Read the machine-interface contract