Gera District Price Index (GDPI) — methodology

1. Source data

Dataset

HM Land Registry — Price Paid Data

Publisher

HM Land Registry (HMLR)

Licence

Open Government Licence v3.0 (OGL v3.0). Contains HM Land Registry data © Crown copyright and database right 2026. This data is licensed under the Open Government Licence v3.0.

Reference period

Rolling 12 months ending April 2026 (May 2025 – April 2026 inclusive)

Coverage

2,188 postcode outcode districts in England, Wales, Scotland and Northern Ireland with ≥20 qualifying transactions

2. Step-by-step computation

1. Step 1 — Download PPD CSVs

   Download the annual PPD CSVs for the rolling 12-month window from https://www.gov.uk/government/statistical-data-sets/price-paid-data-downloads. The PPD has no column headers; the format is documented at gov.uk/guidance/about-the-price-paid-data.

2. Step 2 — Filter to standard residential

   Retain only rows where:

   • Property type ∈ {D, S, T, F} (Detached, Semi-detached, Terraced, Flat/Maisonette). Exclude type O (Other) as it includes commercial/mixed-use.
   • Transaction category = A (Standard Price Paid). Exclude category B (Additional Price Paid, e.g. compulsory purchase).
   • Price ≥ £10,000 and ≤ £50,000,000 (sanity bounds).
   • Date within the 12-month window (May 2025 – April 2026).

3. Step 3 — Extract outcode

   From the full postcode (column 4, 0-indexed), extract all characters before the first space character. Normalise to uppercase. Examples: "SW1A 1AA" → "SW1A"; "M1 1AD" → "M1"; "LE12 7AB" → "LE12".

4. Step 4 — Compute outcode medians

   For each outcode, sort all qualifying transaction prices and take the median (middle value for odd counts; mean of two middle values for even counts). Exclude any outcode with fewer than 5 total transactions. For property-type medians, require ≥3 transactions of that type.

5. Step 5 — UK outcode median

   Compute the median of all outcode medians (after step 4). As of April 2026: £288,675. This is the GDPI denominator — it changes with each monthly update.

6. Step 6 — Compute GDPI

   GDPI = round(outcode_median / UK_outcode_median × 100). Rounded to the nearest integer. Published alongside the outcode median price and transaction count on each district page.

3. Interpreting the GDPI

4. Limitations and caveats

• Sold price, not asking price. The GDPI uses the actual registered sold price, not listing or asking prices. It reflects what buyers paid, not what sellers sought.
• 12-month rolling window. The median is computed over 12 months. Very recent market shifts (last 1-3 months) will be under-weighted relative to the full window.
• Outcode coverage varies. Urban outcodes have hundreds of transactions; rural outcodes may have only 5–20. Lower counts mean wider confidence intervals around the median. The count is shown on every page.
• No mix adjustment. The outcode median is not mix-adjusted for property type or size. An outcode that sells disproportionately more detached homes will show a higher GDPI than mix-adjusted data would produce.
• New builds included. The PPD does not separate new-build from resale for the purposes of this aggregation. New builds typically transact at a premium.
• Not a valuation. The GDPI and median prices are statistical aggregates, not property valuations. They should not be used as a basis for financial decisions without independent professional advice.

5. Reproducibility

The generation script that produced the current data is documented at scripts/growth/gen-uk-ppd-outcode.mjs in the GeraRent repository. The input data are the publicly downloadable PPD CSV files listed at https://www.gov.uk/government/statistical-data-sets/price-paid-data-downloads. No proprietary data is used — the GDPI is fully reproducible from the public source alone.

6. Related pages

• All 2,188 UK postcode districts by GDPI
• UK house prices by local authority (360 areas, UKHPI)
• Gera Liveability Index methodology