How the report arrives at its figures, in plain words. Only general formulas appear here, no user data. The exact definition of every term, as the code computes it, is in the glossary.
Each property is simulated year by year, up to 25 years. Year 1 is the first year of letting. The report’s headline figures (the verdict, the return) are computed for the sale year you choose (25 by default).
All amounts are in current euros: they are not adjusted for inflation, except the indicative “after inflation” return of the comparison with stocks and bonds.
The rent collected allows for the months without rent (works at the start, vacancy between two tenants): a number of months per year, applied every year. The costs run for 12 months.
The operating costs are the co-ownership charges (syndic), utilities, property tax (taxe foncière), home insurance, the accountant and bank fees. Rent, property tax and the syndic charges each grow at their own rate; the other costs stay constant.
Profit also takes off the loan interest and the borrower insurance. Cash flow also takes off the principal repaid: it is the money that is really left.
Rent collected = monthly rent × (12 − months without rent), then × (1 + growth) every yearCosts = (syndic + utilities + property tax + insurance + accountant + bank fees) × 12Profit = rent collected − costs − interest − borrower insuranceCash flow = profit − principal repaidFor a loan already signed, the report uses the bank’s monthly principal and interest figures for year 1, then keeps their sum as a fixed payment: each later year’s interest is recalculated (balance left × rate).
For a planned purchase, the yearly payment is computed with the annual formula below, then divided by 12. This is deliberate (it matches the reference calculator used for these properties): a bank’s monthly schedule can differ by a few euros.
Borrower insurance is counted as a cost, like interest (0.15% of the amount borrowed per year by default). At the sale, the balance left is repaid, with early-repayment and release fees (a percentage of the balance left, 1% by default).
The money left in the account (the SCI’s, or your personal account under LMNP and micro-foncier) can earn a rate you choose (0% by default). When the account runs short, either you top it up yourself (those top-ups count as money you invested), or a short-term lender covers it at the rate you enter.
Yearly payment = L × i ÷ (1 − (1 + i)^−n) monthly payment = yearly payment ÷ 12Interest of the year = balance at the start of the year × i; principal repaid = yearly payment − interest(L = amount borrowed, i = annual rate, n = term in years)Taxable profit starts from the profit, adds the interest earned by the company’s account and takes off depreciation and the deductible interest on the partner’s current account (compte courant d’associé). Purchase fees (notary, agency, other fees) and declared repairs are deducted in the first year.
Depreciation: the building straight-line (2% of the purchase price per year by default), declared improvement works over 15 years and declared furniture over 7 years by default. Each line stops once its cost is fully written off.
Corporate tax is 15% up to €42,500 of profit and 25% above (the reduced rate assumes the company meets its conditions). A loss is carried forward to the following years. When the SCI owns several properties, their results are added up in a single tax calculation.
Partner’s current account: the money you lend the company can earn interest. The company deducts that interest (up to the capped rate if you enter one) and you personally pay the flat tax on it (31.4%).
At the sale, the capital gain is computed on the net book value (purchase price + declared improvement works and furniture − depreciation already taken) and is added to the year’s result, taxed at IS. The company then repays your current account, tax-free; what it pays you beyond that is taxed personally at the exit rate (30% by default). With several properties, this exit tax is split between them by their fair share (Shapley value).
IS = 15% × min(profit, €42,500) + 25% × max(profit − €42,500, 0)Capital gain = sale price − agency fee − early-repayment fee − net book valueExit tax = exit rate × max(amount paid out − current account repaid, 0)The property is owned personally and let furnished. Each year, the taxable result is the rent minus the actual costs (interest and insurance included; the purchase fees in the first year), minus past losses, minus the depreciation of the building, the improvement works and the furniture. Depreciation cannot create a loss: the unused part is carried forward with no time limit.
That result is taxed at your marginal income-tax rate, plus social contributions (18.6% under the 2026 rules). Part of the CSG (6.8 points) is deductible the following year: the tax saved is counted the year after. The interest your account earns, when it is positive, is subject to the flat tax (31.4%).
At the sale, the capital gain follows the rules for private individuals: 19% income tax and 17.2% social contributions, each reduced by an allowance for every year held beyond the fifth (income tax exempt after 22 years, social contributions after 30 years), plus a surtax above €50,000 of taxable gain (after the allowance). The purchase price is raised by the flat 15% works allowance after more than 5 years of ownership, or by the actual works not deducted if that is better. The depreciation actually deducted on the building and the improvement works (not the furniture) is added back to the gain (2025 Finance Act; except student residences, senior residences and EHPAD).
The tool flags the year when receipts exceed €23,000, the threshold above which you could fall under LMP (professional furnished letting) status. That status is not simulated: the figures are still computed under LMNP.
Taxable result = rent − actual costs − past losses − usable depreciation (≥ 0)Tax of the year = taxable result × (marginal rate + 18.6%) − CSG saving of the previous yearThe property is owned personally and let unfurnished, with at most €15,000 of rent a year: the simplified regime for rental income (revenus fonciers). A flat 30% allowance replaces every cost: the taxable income is the rent collected excluding charges (without the part of the charges the tenant pays you back with the rent) minus 30%. No actual cost is deducted — no interest, no property tax, no works — and there is no depreciation and no loss.
That income is taxed at your marginal income-tax rate (30% by default, editable in the editor), plus 17.2% social contributions: rental income is not affected by the 2026 rise to 18.6%. Part of the CSG (6.8 points) is deductible from your income the following year (CGI art. 154 quinquies II): the tax saved is counted the year after. The interest your account earns, when it is positive, is subject to the flat tax (31.4%); overdraft interest is not deductible from anything.
In reality the €15,000 cap covers every unfurnished rent of your household. The tool only knows this property: it checks the cap on this property alone, refuses a first-year rent above it, and flags the year when rising rents cross it. From that year the régime réel would be mandatory; the figures are still computed under micro-foncier. Even below the cap you can opt for the régime réel (binding for 3 years): it is often better when interest and costs exceed 30% of the rent; the tool only simulates micro-foncier. Micro-foncier is not open to properties under certain tax incentive schemes (Pinel, Malraux, historic monuments…).
At the sale, the capital gain follows the rules for private individuals, as for LMNP (19% income tax and 17.2% social contributions, holding-period allowances, a surtax above €50,000 of taxable gain), with nothing to add back. The purchase price is raised by the better of the flat 7.5% of the price and the actual purchase costs, and by the better of the flat 15% works allowance (after more than 5 years of ownership) and the actual works — only works invoiced by companies count (the tool assumes you have the invoices).
Three calculation choices still await an accountant’s confirmation: the CSG deductible the following year, and these two “better of” options at the sale.
Taxable income = (rent collected − charges paid back by the tenant) × (1 − 30%)Tax of the year = taxable income × (marginal rate + 17.2%) − CSG saving of the previous yearThe default values come from INSEE series (the French statistics office), and each can be changed in the editor. The property’s value grows every year at its own rate, from its value after works.
The return shown is a money-weighted rate of return (the IRR of your own money). It takes into account when each euro went in: the initial cash, then every top-up paid later. Nothing is paid out before the sale: the money earned each year stays in the account and earns the chosen rate.
For an SCI it is given at three stages: before tax, after company tax, and “if you sell”, after all taxes; the last one is the headline figure. Under LMNP a single return is computed: “if you sell”, after all taxes. Under micro-foncier the report also shows the return before tax and after tax, and the headline is “if you sell”, after all taxes.
The net gain is what you get back at the sale, minus everything you put in. The breakeven year is the first year in which a sale would give you back at least everything you put in, after tax.
Find R such that Σ cash in(t) × (1 + R)^(N − t) = final amount (t = 0 … N)Net gain = amount received at the sale − initial cash − top-ups paidThe report places the property’s return against two reference investments, after tax and fees, before inflation. By default: stocks 10% per year, bonds 4.5%, tax and fees 40%.
Two bands follow: “not worth it”, just above bonds (the property barely beats a risk-free investment), then the “real estate range”, up to the net return of stocks. The property’s point is its “if you sell” return, already after all taxes. The 1.5-point gap is a fixed constant, not an input.
The after-inflation return, shown as an indication, applies the same “tax and fees” cut to the property’s return as to the investments, then simply subtracts inflation, without the Fisher formula: r × (1 − F) − I.
Net bonds = B × (1 − F) Net stocks = S × (1 − F)“Not worth it” = [net bonds; net bonds + 1.5 points]“Real estate range” = [net bonds + 1.5 points; net stocks](B = bond rate, S = stock return, F = tax and fees)On these points the calculation deliberately differs from the convention of the reference textbooks. Each difference is flagged in the glossary, with its explanation.
What the model does not do, or does in a simplified way:
The notation and conventions follow these references: