01What kind of price are you seeing?
Compare apartments with apartments and houses with the same type of house. Asking prices use euros per square meter of living area; standard land values use euros per square meter of land. A figure for an apartment construction-year group is not a total price for every apartment in a city. The tables show the groups actually available.
02Median and middle half of offers
The median is in the middle of the sorted observations: half are below it, half are above it. P25 to P75 comprises the middle half. Example for explanation, no current market data: For 2,000, 2,500, 3,000, 3,500 and 4,000 €/m², the median is 3,000 €/m² and the middle half is between 2,500 and 3,500 €/m². This range is not a statistical confidence interval for the entire market.
03Why ten offers don't automatically reflect the market
Our metrics use appropriate offers from observed sources that were last seen within 30 days. Known duplicate groups are cleaned up; the unique identity of each property is therefore not proven. A source or a new construction project can provide a large part of the sample. Therefore, open “Sample and Limits” or “Restricted Sample” on the key figure. Concentration, dispersion and excluded observations are listed there. An observation date does not prove that the provider posted a new advertisement on that day.
04Separate ordinary rent and special rental offers
Furnished apartments, temporary accommodation, service packages and rooms in shared flats cannot simply be compared with an ordinary unfurnished apartment. A total rent or rent including heating is not a verified rent excluding heating and operating costs. In the ordinary asking-rent comparison we exclude identified special offers and unclear amounts; as a result, the sample may fall below the publication threshold of ten observations. Asking rents and the official rent index remain different types of data.
05How to check for a noticeable difference
Check the type of property, year of construction, condition, area, special rights, location accuracy, time and composition of the sources. Different portals can come to different results. A high proportion of new construction or a dominant provider is an explanation, but not yet independent market confirmation. We do not automatically replace conspicuous values with numbers from another portal. We mark contradictions in official total values and do not use the value in question as a general market price until it is clarified.
06What exactly is the location?
A postal code, street midpoint or district centre is not an exact property address. Such points cannot confirm assignment to a small reference-value zone. Land values and real estate reference values refer to described zones or standard properties. An unweighted median of zones is neither a market price weighted by land area nor one weighted by sales.
Frequently asked questions
Is the sample size the number of all apartments offered?
No. n counts observations from our sources suitable for this comparison. It is neither the whole market nor the number of listing cards approved for public display.
Why does a rental key figure disappear after an audit?
If fewer than ten observations remain after excluding unsuitable or unclear offers, we do not show a median. The underlying data sets are retained.
No legal or tax advice
The key figures are an orientation based on observed sources and do not replace an individual valuation. Prices for individual offers remain those provided by the respective provider.
Next steps and background
Data sources
Official source · Our own calculation · Our own analysis · DDORF estimate → Methodology
- Official sourceGrundstücksmarktdaten NRWOfficial comparison groups, reporting years and data licence; not current asking prices.View source(opens new window)