Where the numbers come from

The three rules

1. Official source first. Every rate, bracket and coefficient is taken from the official document (Portal das Finanças, Diário da República, legal instruments) and cross-checked against a second reputable source. Only then does it go into the calculators.
2. We never invent a number. When a value can't be verified, the calculators show it as “to confirm” — we don't fake precision. Market estimates (construction costs, fees) always appear as ranges, never as one exact figure.
3. Updates with the date on display. Euribor is checked automatically every week (the value is the monthly average published by the ECB, so it changes once a month); the tax tables change with the State Budget and are swapped in as a block. Every table keeps the date it was verified — it's in the right-hand column, below.

The formulas, no secrets

IMT: price × marginal rate − deductible portion (parcela a abater), using the practical tables from Ofício Circulado 40129/2026; above the last bracket a flat rate applies to the whole value. Monthly payment (prestação): the French amortization system (sistema francês), P = C·i/(1−(1+i)⁻ⁿ), where i = TAN/12 and TAN (nominal annual rate) = Euribor + spread — a negative Euribor is passed on in full, as required by Law 32/2018 (the calculator floors the TAN at zero; below that the law requires it to be deducted from the capital instead). Capital gains (mais-valias): sale price − purchase price corrected by the official coefficient − documented costs; half the gain is added to your IRS (personal income tax) brackets, plus the additional solidarity rate when taxable income reaches it (art. 68-A of the CIRS). We round to the cent, half up, only at the end of each calculation.

We always show the TAN and never the TAEG (the Portuguese APR-equivalent, Taxa Anual Efetiva Global) — the TAEG depends on each bank's insurance and fees, and any site that “guarantees” you a rate is selling you something. We are not credit intermediaries and we don't take money from banks.

Honest limits

The calculators do the maths, not the advising. Cases with particular wrinkles (property swaps, undivided inheritances, non-residents, specific municipal exemptions) should be confirmed with a certified accountant, the notary, or the AT (Autoridade Tributária, Portugal's tax authority). If you find an outdated value, tell us — we'll fix it and it stays on record.