How We Calculate Your Valuation

1. The starting point: real completed sales

Every valuation starts with HM Land Registry's record of actual completed sales in your postcode sector — the price a comparable property legally changed hands for, not an asking price, not another site's estimate. We use your postcode sector (the first part of your postcode, e.g. WD17 from WD17 3JT) as the base geographic unit, since it's granular enough to capture genuine local variation without so few sales that the result becomes unstable.

2. Bedroom-adjusted benchmarking

A raw £/sqft average across every sale in a sector mixes 1-bed flats with 5-bed houses and produces a misleading figure. We benchmark against sales of a similar bedroom count to your property, so a 3-bedroom semi is compared against other 3-bedroom semis nearby, not diluted by unrelated property sizes.

3. Time-adjustment via the UK House Price Index

A sale from three years ago is a real data point, but the market has moved since. We scale every historical comparable sale up or down using the UK House Price Index for the relevant period and region, so a 2023 sale is expressed in today's terms before it's used, rather than treated as if it happened yesterday.

4. Radius expansion, only when needed

We start with the tightest reasonable radius around your property and only widen it — and correspondingly relax the time window — when there aren't enough genuinely comparable sales nearby to produce a statistically reliable median. This is why a valuation in a dense urban postcode sector (lots of recent sales close by) tends to carry a higher confidence score than one in a sparse rural area, even for similarly-priced properties.

5. Plausibility checks

Before a comparable sale is used, we check it against a sqft-plausibility gate — a sale record with an implausible floor area for its stated bedroom count (a data-entry error somewhere upstream, which happens in any large public dataset) is excluded rather than allowed to skew the median. Comparable sales are also ordered deterministically, so re-running the same valuation twice returns the same result rather than an arbitrary tie-break producing slightly different comps each time.

6. The confidence score

Every valuation carries a confidence score based on how many comparable sales it's built from, how close by and how recent they are, and how tightly they agree with each other. A high score means dozens of recent, nearby, similar-bedroom sales all pointing to a similar figure. A low score means the radius or time window had to widen significantly to find enough comparables at all — treat that number as a rougher estimate accordingly.

What this can't see

This is the important part. Our methodology is entirely statistical — it has no way to know:

• Your property's actual internal condition (a renovated kitchen, damp, a rewire, an extension not yet reflected in comparable sales)
• Your specific lease terms if leasehold (remaining term, ground rent, service charge — see our leasehold vs freehold guide)
• Very recent hyper-local shifts a broader comparable-sales dataset hasn't caught up with yet (a new station, a major local employer arriving or leaving)
• Anything a physical inspection would catch — structural issues, subsidence risk, roof condition

For anything you're about to make a financial decision on — buying, selling, remortgaging — see our guide on when you need a RICS survey instead.

Data sources

HM Land Registry Price Paid Data (Crown copyright, Open Government Licence), the UK House Price Index, and EPC register data (used to calibrate habitable-room counts where bedroom data is incomplete). See our Privacy Policy for how this data is processed.