Methodology: This is how our numbers are created

Official source, our own calculation, our own analysis and DDORF estimate identify where our figures come from. We distinguish them consistently in text, charts and tables. Each figure has a symbol and label, so the distinction does not depend on colour alone.

We never show asking prices and actual purchase prices in the same graphic without a clear separation. The source and status are listed under each key figure.

Der WertPilot startet nicht bei Angebotspreisen, sondern beim offiziellen Immobilienrichtwert (IRW) des Gutachterausschusses. Dieser gilt für eine Norm-Wohnung in Ihrer Lage. Weicht Ihre Wohnung von der Norm ab, passen wir den Wert mit den veröffentlichten Umrechnungskoeffizienten an. Die tatsächlich angewendeten Anpassungen und nicht berücksichtigten Merkmale stehen im Ergebnis.

1. Step 1Real estate guideline valueStarting value for location and standard object on the key dateOfficial source
2. Step 2Adjustment factorsYear of construction, living space and - depending on the city - modernization, equipment, floorDDORF estimate
3. Step 3RangeSource and limitations shown with each resultDDORF estimate

The range follows the basis stated with the result. Published feature ranges, model assumptions and missing inputs may affect its width. The reliability rating alone does not determine a fixed width; additional inputs do not automatically narrow the range.

The rating shown with the result describes the data basis, not guaranteed accuracy. The categories below are qualitative explanations, not fixed percentage intervals.

Listing data shows the prices asked in property listings. It responds to market changes faster than official data, but represents asking prices. Our own analysis based on publicly available source data.

1. 01Our own analysisOur own analysis based on publicly available source data. The publication of photos and texts requires the necessary usage rights and releases.
2. 02ComparabilityThe key figures describe the reported sample. They are not official market values and are not a complete reflection of the market.
3. 03Median instead of meanWe show the median: half of the offers are below and half are above. Individual luxury objects hardly shift it - unlike the average. P25-P75 shows the middle half of the offers.
4. 04At least n ≥ 10Below 10 listings, we show no figure or chart. We explain that the sample is insufficient and offer an alternative, such as the neighbouring district or whole city.

△ Asking prices from listings, not actual sale prices.

For cities without a published or usable rent index, we estimate a typical existing rent. The basis is the net rents from the census 2022 (key date 15.05.2022) for each area and year of construction. We derive the development since then from our offer data.

We checked the method against 234 calculations in 13 cities in the region with a rent index. The average deviation was 7.7%; in 80% of cases, the rent-index value fell within the displayed range of ±12.6%. These reference points were also used to tune the level factor. The figures are therefore not an independent test on new apartments and do not guarantee accuracy for your property.

Rent estimate figures: our own analysis; model description reviewed on 12 October 2026. Census reference date: 15 May 2022. The comparison figures use the same reference points as model calibration; they are not an independent accuracy test.

Prices actually paid come from the purchase price collection of the valuation committees: Notaries report every purchase contract, the valuation committees evaluate them and publish average and guideline values, usually once a year. We show these values with the year and source - separately from the asking prices.

The price development on the city pages follows the published land values, real estate values and purchase prices from BORIS NRW and the property market reports. We always refer the change to the previous published year; if a year is missing, “since” is included with the comparison year.

The general DDORF score is not published. The finder and business profiles are in closed testing. Observed listings and price changes prove neither sales quality nor the full size of an agency portfolio.

Our numbers have limits. We name them instead of hiding them.

• No viewing. Only details collected and implemented in the city model are included. Layout, damage, noise and views are not automatically assessed.
• Stichtag. Guideline values apply as of the key date 01.01. They do not yet reflect market movements after that.
• Unusual properties. We do not automatically evaluate monuments, leaseholds, residential rights or apartment buildings.
• Missing guidelines. Where there is no property reference value, we do not calculate. In Jüchen and Rommerskirchen, for example, we do not show automatic valuations, but rather guideline land values and - if there are enough offers - asking prices.

The WertPilot provides an indicative assessment - not a market value report according to § 194 BauGB. You usually need an appraisal for inheritance, divorce, tax office or court.

DDORF WOHNEN is not an authority and does not act on behalf of the valuation committees or the cities. We do not use logos or coats of arms of the data sources.