Every figure has a source.
Every verdict, a calculation.

01

Who does what

02

Market figures

Every market value is stored with its source, link, period and type. The type is always shown next to the figure:

Actual sales

Prices of recorded transactions. This is the reference Maison uses first to compare a property.

Estimate

Price computed by a valuation website. Useful, but less reliable than sales.

Listings

Asking prices or rents, not achieved ones.

Index

Relative price change, without a value per m².

Survey, official statistics

Rents, incomes or vacancies published by an observatory or a statistics office.

When a town has no series of its own, Maison uses the national series and says so: “national benchmark, not a local estimate”. No curve is extended beyond the published points.

03

The verdict, formula by formula

The verdict applies your profile (down payment, loan, vacancy, filters) to the first costed scenario of each listing. Defaults when you have not set them: down payment 20% of the price, loan at 3.8% over 25 years, insurance 0.30% a year, purchase costs 8%, vacancy and management 10% of rents.

1. Total cost = price + purchase costs + works + other costs.
2. Net operating income = annual rents × (1 − vacancy and management) − property tax − service charges and upkeep.
3. Net yield = net operating income ÷ total cost. This is the yield shown first.
4. Gross yield = annual rents ÷ total cost. Shown second, for comparison with the market.
5. Monthly payment = constant loan annuity + borrower insurance.
6. Monthly cash flow = net operating income ÷ 12 − monthly payment, before tax.
7. Gap to the market = the property's price per m² ÷ reference price − 1. Maison's actual-sales reference takes precedence over the one suggested by the assistant.
8. Value in a downturn = price × (1 + steepest historical fall in the series). A risk benchmark, not a forecast.

04

What Maison does not make up

• Missing data is shown as “not available”, “n/a” or “to be documented”, never replaced by zero.
• When property tax or service charges are missing, the net yield is shown as a maximum (“≤ 7.4%”) and the report says that yield and cash flow are overstated.
• When works are not costed, the report says so: the total cost remains to be confirmed after a visit.
• Every cost has a status: confirmed (given by the listing or a document), estimated (computed from a cited source, or from the cost rates in your profile), or unknown.
• All the figures in a report, verdict and simulation alike, come from the same calculation engine: a property never has two different yields on the same page.
• A property that does not meet all your criteria is never mixed with the selected ones: it appears separately, “Outside your criteria, for information”.
• Two measures of price per m² (a historical series and a sales reference) are shown side by side with their type, without being mixed.
• A listing link blocked by a website is never presented as verified.
• A listing that gives two prices is never “meets your filters”: every calculation uses the higher price and the property stays “to be completed” until the price is confirmed in writing.
• Cash flow is broken down line by line (rents, vacancy and management, property tax, charges, loan payment, insurance): anyone can redo it by hand.
• The “Data reliability” score measures the quality of the information (price reference, verified listing, costed expenses, complete data, consistent price), not the quality of the investment.
• Scenarios: optimistic (unknown costs left at zero), central (property tax of one month's rent and charges of 8% of rents when they are missing), cautious (highest price, tax of 1.5 months, charges of 12%, works of 10% of the price, vacancy +5 points), then five tests: three months without a tenant, unexpected works of €15,000, charges +30%, rate +1 point, rent −10%. These rules are written under each bar; they are not facts.
• Comparable sales: only actual DVF sales of a single flat or a single house, of similar size, in the same town, over 36 months, at least 8 sales. The range shown is the interquartile range of their prices per m² multiplied by the property's floor area, with the list of sales. Without enough sales, or in Alsace-Moselle (not covered by DVF), Maison says so instead of estimating.
• Location: straight-line distance between the centre of the town and the centre of the nearest urban hub (large French and Swiss cities). It says nothing about the street or the travel time; you can make it a filter in your profile.

05

Limits

• A town-level reference does not replace comparables of the same type in the same street.
• Achievable rents, works and the feasibility of a split are assumptions: planning permission, housing standards, rent controls and co-ownership rules remain to be checked.
• A past fall does not predict the future.
• Maison gives no investment or financing advice and contacts no agency.

06

Privacy

For the daily search, listings are searched from anonymous tasks: an identifier, towns, a budget, a strategy and your instructions. Neither your name, nor your e-mail address, nor your household appears in them. Only Maison links the task to your search. Every report states when it was produced.