How much is my house worth?

To know what a house is worth, start by separating two things: an estimate and a price.

Before the sale, market value is not an observed number. It is a reasoned estimate of the price the property could achieve under normal market conditions, between informed parties and without special circumstances.

The actual price only comes into existence when buyer and seller reach an agreement and the transaction takes place.

That estimate begins with the right references. It is not enough to look for properties of the same type or in the same parish. You have to identify recent transactions of genuinely comparable homes and understand what brings each of them closer to your house — and what sets them apart.

Then come the adjustments. A property can look comparable on paper and stop being so once you know the house, its location or the features that actually shape a buyer’s decision.

A serious analysis does not try to manufacture a precision the data cannot support. It seeks a conclusion that can be explained, substantiated and defended.

A bank appraisal answers a different question. It is carried out by licensed appraisers for specific purposes, notably lending, and should not be confused with the study that supports a decision to sell.

The value of a house is determined, first, by what the data can measure: location, floor areas, type, floor level, year of construction, whether there is a garage or a lift.

But two homes that are identical on paper can have very different values. Because a significant part of what decides a purchase is not in any database.

The exact location. Not just the parish. The street, the side of the street, and what you see from the window.

The light. Sun exposure can completely change how a home feels.

The view. A living room with a sea view and the neighbour’s living room without one are not necessarily worth the same.

The noise. Some things can only be noticed inside the property — and sometimes only at the right time of day.

Condition and quality. Some renovations add value; others only appear to.

The floor plan. Well-distributed square metres can be far more valuable than the same area poorly used.

Surroundings and privacy. The building, the access, the proximity of other constructions — and even what might one day be built next door.

Demand at that moment. The same property, a few months earlier or later, can meet a different market.

That is why the question “how much is a three-bedroom flat in Cascais worth?” has no serious answer.

The serious question is a different one:

How much is this three-bedroom flat worth — on this street, in this condition, at this moment?

Determining the market value of a house is not a matter of finding similar properties and taking an average.

In residential property, one of the main references is the comparative method, which starts from actual completed transactions of comparable homes.

The challenge lies in understanding what is genuinely comparable.

Two properties can be of the same type, have similar floor areas and sit on the same street — and still not serve equally well as references for estimating the value of a house.

The exact location, the condition, the view, the light, the layout, the characteristics of the building or the moment each transaction took place can change the reading completely.

Some references seem relevant and stop being so once you know the property better. Others become important for reasons that a search by area, type or price per square metre cannot reveal.

This is where the work of analysis comes in.

You have to separate what genuinely helps to understand the value of the house from what merely looks similar, cross that information with the actual property, and interpret it in the context of the market at that moment.

That is precisely the problem a Comparative Market Analysis sets out to solve.

Not through an automatic formula, but through real information, knowledge of the property and judgement in interpreting the data.

The data is the starting point.

Knowing which data matters, which does not, and what it means for that particular house — that is the work.

The problem with simulators is not that they are digital, automatic or unsophisticated.

It is much simpler than that.

They do not know the house.

A simulator works with the information it can turn into data: location, area, type, a few features of the property and whatever market data it has access to.

From there, it looks for patterns, establishes relationships and produces a number.

The calculation may be sophisticated. It may have thousands of data points behind it. It may present a range, charts and even an appearance of great precision.

But it is still missing an essential part of the information.

The light is not in the registered floor area.

The noise does not appear in the property type.

The real quality of a renovation cannot be read from the year it was done.

A database does not know whether a living room feels spacious or cramped. It cannot sense the privacy of a terrace. It does not know the real condition of the building. It does not know what you see from that window, or what happens on that street at the end of the afternoon.

And it cannot gauge the effect all of this will have on someone considering buying the house.

Similar in a database does not mean comparable in the market.

There is one further, fundamental difference.

An algorithm has no feelings. Buyers do.

They are people who walk into a house. They notice the light. They open the windows. They listen to the street. They compare spaces. They imagine their life there. They like one house more than another and decide how much they are willing to pay.

Those decisions are what make the market.

So the question is not whether the algorithm is good or bad at calculating.

It is that we are asking it for an answer the available data does not allow it to know.

A similar principle applies even in the professional framework for appraisals carried out for financial-sector institutions. The law requires the report to clearly identify the scope of the inspection made of the property, describe its characteristics and surroundings, and substantiate the methods, enquiries and data used.

When a value has to be professionally sustained, what was actually observed matters.

And when this much is at stake, small differences represent a great deal of money.

On a €1,000,000 house, a 5% difference is €50,000.

On a €1,500,000 house, it is €75,000.

A simulator can produce a number.

But a number produced without knowing the property is not a market study.

The asking price is a decision. The sale price is an outcome.

When a property comes onto the market, someone chooses how much to ask for it.

That number may be close to what the market can sustain. It may be above. It may be below.

That is why listings are useful information for understanding the competition at that moment — but they are not proof of value.

A concrete example: in the Cascais and Estoril area, over the twelve months to July 2026, the average price of existing homes actually sold was 26.6% below the average asking price of all those on the market.

This indicator is called the price gap, and it measures the mismatch between supply and real demand. It does not mean that every home sells 26.6% below asking. It means something more revealing: a significant share of what is listed carries prices the market is not validating. The homes that sell, sell closer to reality. The rest wait — in the same area, the average time between listing and sale was five months.

In other words, whoever sets the price of their home by looking at the listings around it is also using, as a reference, the properties that are failing to sell.

There is also a simplistic idea worth avoiding: starting higher does not automatically mean ending up selling for less.

The relationship between initial price and final price is more complex. Research consistently finds a link between higher listing prices and longer time on the market. As for the effect on the final price, the findings cannot be reduced to a simple rule.

The mistake, however, cuts both ways.

If a house enters the market above what buyers can sustain, it may stay on sale longer, lose its initial impact and start to raise an awkward question: why hasn’t it sold yet?

If it enters below what buyers would have been willing to pay, the consequence may be even less visible.

The house sells.

The owner is pleased.

And may never know how much money was left on the table.

That is why selling quickly does not, in itself, prove the price was right. Likewise, staying on the market too long does not simply mean “the right buyer” was never found.

The aim is not to ask for more.

Nor is it to sell faster.

It is to position the house so that the market can recognise the full value it is able to sustain.

Listed properties show you who your house will be competing with.

Completed transactions show you what buyers and sellers actually agreed to.

To confuse the two is to confuse expectation with evidence.

Today it is very easy to get a number for a house.

It may come from a simulator, a portal, an automated report or a so-called “free market study”.

The hard part is understanding what really lies behind it.

Before trusting an estimate, ask six questions:

1. Is it based on completed transactions, or mainly on asking prices?
2. Are the properties used genuinely comparable, or merely similar in the data?
3. How recent are the references used?
4. What adjustments were made, and why?
5. Can the person presenting the number explain how they arrived at it?
6. Was the number estimated independently of the commercial outcome?

The sixth question deserves particular attention.

Whoever presents the study may have an interest in winning the listing.

Whoever receives the study would naturally prefer to believe their home is worth the higher number.

Both incentives can push in the same direction.

A higher number can be, at the same time, easier to present and more pleasant to hear.

That is precisely why the conclusion has to be able to survive the interests of both parties.

Faced with two different estimates, the most useful question is not:

“Which one says my house is worth more?”

It is:

“Which one can better demonstrate how it arrived at that value?”

This is also where it pays to look closely at the many offers of “free market studies”.

The problem is not simply that they are free.

It is whether there was actually a study.

If the process begins by asking for a few details or documents about the property, produces a report and ends in a sales call, there is a legitimate question to ask:

Was the main purpose to study the house — or to create an opportunity to reach the owner?

A report can run to many pages.

It can include photographs, maps, charts, averages and an impeccable presentation.

None of that proves that anyone knew the property, selected comparables with judgement, analysed the differences and built a conclusion independent of the commercial result they hope to obtain.

There is an important difference between studying the market to reach a conclusion and choosing a conclusion that makes it easier to reach the owner.

A serious study starts with the house.

Not with the form.

Not with the report.

And above all, not with the number that would be most pleasant to hear.

Before asking how much they say your house is worth, ask how they arrived at that number.

The honest answer is simple: a serious estimate can only be reached by studying the actual property and the market in which it will be sold.

There are things an owner can do alone — and should.

Follow the local market. Know the properties that are for sale. Understand the competition. Question average prices per square metre, and avoid confusing asking prices with prices actually accepted.

And, faced with any estimate, ask the right questions.

Then there is a part that calls for another level of analysis: selecting the right comparables, knowing completed transactions, visiting and understanding the property, justifying the differences and relating all of it to the current market.

That is where a mere number ends and a substantiated conclusion begins.

One last distinction matters.

A Comparative Market Analysis is neither a bank appraisal nor a certified appraisal.

Appraisals for those purposes are carried out by licensed appraisers qualified to do so.

A Comparative Market Analysis serves a different decision: understanding the value the market can sustain, and supporting the sales strategy.

That is the work we do at CasaPlace.