Data sources

Calculated directly from the numbers you enter using standard, published formulae. No external data required.

Calculated using published HMRC rates and thresholds for the 2025/26 tax year (England, Wales & Northern Ireland — Scotland has different bands). Rates are reviewed periodically rather than pulled from a live feed; see the calculator pages for the exact assumptions used.

Calculated using published 2025/26 Child Benefit rates and the High Income Child Benefit Charge thresholds (£60,000–£80,000), and the standard Marriage Allowance transfer rules. Deterministic, rule-based calculations — not means-tested benefits like Universal Credit, which are out of scope due to their many household-specific components.

Net monthly income is calculated from each applicant's gross income using the same salary take-home engine as the Salary Calculator — it assumes straightforward PAYE employment income with no pension contributions, benefits or other income. This is compared against the ONS benchmark expenditure, Council Tax, mortgage payment and credit commitments to show an indicative monthly surplus or deficit. This is explicitly not a lender affordability assessment — lenders apply their own stress rates, expenditure assumptions, income verification and policy rules, and a positive figure here does not indicate any lender would approve the borrowing.

Historic sale prices for England & Wales (from 1995, updated monthly) via HM Land Registry's live, unauthenticated Linked Data API — no bulk file import. Matched by postcode only, not full address/UPRN (the API has no UPRN field), so results shown for a property are best-effort address-text matches within that postcode's sales, and 'comparable sales' means other sales at the same postcode rather than a true geographic radius search. Open Government Licence for prices; the address fields carry a separate Royal Mail/Ordnance Survey restriction limiting use to displaying residential property price information, which is what this does — see the attribution note below.

Powers part of the 'Indicative Property Estimate' on the Property tab. When a house name/number is entered and matched to the property's own HM Land Registry sale history, the indexed estimate takes that last sale price and applies the real price movement since then for the property's local authority, from HM Land Registry's UK House Price Index (local authority level, England & Wales; base January 2015 = 100). This only runs when a specific past sale for that exact property was found — without an address match there's no single 'last sale' to index from, so it's correctly omitted rather than indexing an arbitrary sale from elsewhere at the postcode. The comparable-sales method (median of nearby sale prices) runs independently and doesn't need an address match. Open Government Licence.

Phase 1 uses a simplified, rule-based approximation modelled on published ONS Family Spending category patterns — clearly labelled as a benchmark, not your actual expenditure, and not a lender affordability assessment. It excludes mortgage/rent payments and Council Tax to avoid double-counting. If a property postcode is entered, its region is derived from the postcode's area code and used to apply an illustrative regional cost-of-living adjustment (London/South East scaled up, North/Wales/NI scaled down) — this is a modelled adjustment based on general regional spending patterns, not the official ONS region-level Family Spending breakdown. With no postcode, the UK average is used.

An automatic estimate appears as soon as a postcode is entered — no lookup or manual entry required. Covers England and Wales (Scotland and Northern Ireland aren't connected yet — different valuation and billing systems). Individual property bands are legally restricted data (the Valuation Office Agency treats them as personal property data under the Commissioners for Revenue and Customs Act 2005, with no open bulk source), so the estimate uses the most common Council Tax band among properties in that postcode's local area (VOA 'Council Tax: stock of properties' release), priced using official per-authority, per-band charges — MHCLG's 'Council Tax levels set by local authorities in England' for English postcodes, or the Welsh Government/StatsWales 'Council tax levels by billing authority and band' release for Welsh postcodes (Wales has a ninth band, I, that England doesn't). This is clearly labelled as an area-typical estimate, not the confirmed band for the specific property. You can still enter your own figure manually if you know the actual band/charge, which always takes priority over the estimate.

You enter your own monthly rent. Lending Calculator does not scrape Rightmove, Zoopla or any other listings site. A licensed rental-data provider may be added in future via the RentalEstimateProvider interface.