Why online valuation tools get it wrong in Luxembourg

Where do an online estimator's figures come from?

In most cases, from listings. A free tool needs thousands of data points to work, and portal listings are the only source that is both massive and easy to access. Actual sale prices, by contrast, sit in notarial deeds. In Luxembourg, the Administration de l'enregistrement, des domaines et de la TVA sends a monthly extract of the Publicité foncière to the Observatoire de l'Habitat, which completes it with floor areas from the Cadastre (logement.public.lu). These data are published several months late and in aggregated form, by commune and by size band. No consumer tool can read your neighbour's price in them.

The result: the estimator learns what sellers hope for, not what buyers pay. And in Luxembourg, the difference between the two is anything but anecdotal.

How big is the gap between asking price and sale price in Luxembourg?

Between 6% and 18% depending on the commune, and 18% on average nationally. The Observatoire de l'Habitat data for the period from 1 July 2025 to 30 June 2026 leave no room for doubt. In Luxembourg City, apartments were listed at €12,086 per m² and sold at €10,269 per m². In Esch-sur-Alzette, €7,325 listed against €6,427 sold. In Differdange the gap falls to 6%, in Strassen to 7% (data.public.lu).

In other words, a listings-based tool overvalues an apartment in the capital by around €1,800 per m². On 90 m², that is more than €160,000 of illusion. And that is precisely the figure you will remember, because you like it.

An online estimator does not know the sale price. It knows the hoped-for price. In Luxembourg, the two are 18% apart on average.

Want a range based on actual sales, followed by an opinion after a visit? Get my free valuation →

Why does floor area distort the calculation?

Because the price per m² falls as the area rises, and many tools ignore this. Over the same period, an existing apartment under 50 m² sold at €9,435 per m², a 70 to 89 m² unit at €7,534 per m², and a unit of 130 m² or more at €6,441 per m² (Le Logement en chiffres no. 20). Applying the commune average to a large apartment overvalues it by 15% to 20% before anyone has even mentioned its condition.

There is a second, more discreet trap. Listings quote commercial areas, sometimes with a weighted balcony or cellar. Deeds and the Cadastre record other areas. An algorithm that mixes the two compares square metres that are not the same.

Why are houses estimated even worse?

Because there is no reliable official per m² statistic for houses in Luxembourg. The Observatoire de l'Habitat says so itself: for houses, the Publicité foncière gives the total price and the plot size, but not the living area, which makes it impossible to calculate a reliable price per m². The only solid references are average and median prices: €945,274 on average and €870,000 at the median nationally, €1,372,796 on average in the canton of Luxembourg against €729,993 in the North.

A tool that displays a price per m² for your house is therefore inventing a precision that exists nowhere in public data. It builds it from listings, with all the limits described above, and without knowing whether your plot is 3 ares or 12.

What does an online tool see of your neighbourhood, your floor, your energy class?

Almost nothing. Official sale price statistics only go down to commune level from ten sales over twelve months. For a small commune or a specific neighbourhood, the tool extrapolates. Yet in the capital, market surveys show differences that routinely exceed 30% between a neighbourhood like Belair and one like Bonnevoie. An algorithm that knows your postcode but not your street gets the street wrong.

The same goes for what makes a home's real value: floor level and lift, orientation, view, noise, the co-ownership and the works it has voted, the energy class on the energy passport, the quality of the renovation. None of these criteria appears in any usable database. You enter them yourself in a form, with every owner's optimism, and the tool believes you.

So is an online estimator useless?

No, provided you use it for what it is: a starting point, not a price. A good tool gives you a range in two minutes and saves you from gross errors. That is useful to check whether a sale project holds up, or to compare several scenarios before contacting a professional.

What it will never do is decide. The 2026 market is active again, with 1,049 existing apartments and 709 houses sold in the second quarter according to STATEC, but prices fell 2.2% year on year. In a market where buyers compare everything, a 10% error at the start is paid for in months on display, then in a forced price cut.

At Secretimmo, our online estimator was built from actual sales, not listings, and it gives a range, never a single figure. Above all, it is only the first step: a visit follows, because nobody has yet invented the algorithm that can see a roof.

How do you get a reliable price in Luxembourg?

By crossing three sources: the actual sales in your commune, a visit by someone who sells comparable properties every month, and what identified buyers are willing to pay today. The first two correct the gap between listings and deeds. The third is the one no statistic contains, and it is often the one that makes the difference on an unusual or prestige property.

Start with the free estimator at secretimmo.lu/valuation. You receive a range based on actual sales in your area, then we come to see your property to refine it. The valuation is free if a mandate is signed within the following week; otherwise it is invoiced at €600 excluding VAT, because it requires a visit and several hours of work.

This article draws on the official publications of STATEC and the Observatoire de l'Habitat (Le Logement en chiffres no. 20, data from 1 July 2025 to 30 June 2026). The differences between neighbourhoods quoted for the capital come from market surveys and are indicative.

Frequently asked questions

By how much can an online valuation tool be wrong in Luxembourg?

Often by 10% to 20%. The gap between asking and sale prices alone reaches 18% on average nationally over the twelve months to the end of June 2026, and it adds to errors on floor area, neighbourhood and the property's condition.

Do online tools use the prices from notarial deeds?

Rarely. Actual prices are sent by the Administration de l'enregistrement to the Observatoire de l'Habitat, which publishes them in aggregated form and several months late. Most consumer tools therefore rely on listings.

Why is the online estimate of my house so far from reality?

Because there is no official price per m² statistic for houses in Luxembourg: the Publicité foncière does not record the living area. Tools then build a price per m² from listings, without knowing your plot or your property's condition.

Is the Secretimmo estimator different?

It is built from actual sales and gives a range, not a single figure. It serves as a starting point before a visit. The valuation is free if a mandate is signed within a week; otherwise €600 excluding VAT.

Should I be wary of an online estimate that is higher than the others?

Yes. A flattering figure without a visit is a sales argument, not a valuation. Always ask which sales it is based on, over what period and within what radius.