Methodology

How it works

Tax and regulatory calculations are based on primary sources; estimate tools make their assumptions explicit. This page documents the sources, formulas, assumptions and update triggers behind all 36 calculators across 8 markets.

Legislative sources Exact formulas Known limitations Update policy Updated August 2026
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Source-first
Tax and regulatory rates, thresholds and formulas are traced to the relevant law, statutory instrument or official guidance.
⚖️
Estimates, not advice
Results are indicative. Individual circumstances vary — always consult a qualified professional before acting.
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Updated on change
Calculators are updated when underlying legislation or source data changes — not on a fixed schedule.
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Transparent by default
Calculator pages explain their principal formulas, assumptions or source data in the format appropriate to that tool.
General approach

How calculations are built

Tax, lending and regulatory calculations use the relevant primary legislation or official guidance. Rates, thresholds and bands are transcribed from those sources and checked against official examples where available.

Estimate tools, such as renovation budgets and property comparisons, use stated assumptions and public-market indicators rather than a statutory formula. Where a calculation needs professional judgment—for example a land/building split for AfA or a principal-residence test—it shows a reasonable default and asks the user to verify their own position.

All calculations are estimates. They do not constitute financial, tax or legal advice. Real-world outcomes depend on individual circumstances, local variations and professional judgment.

Core formulas

Key calculations used across markets

These are the fundamental formulas used across multiple calculators. Each market then applies local tax rates, thresholds and legislative nuances on top.

Rental Yield
Gross Yield = (Annual Rent ÷ Purchase Price) × 100
Net Yield = ((Annual Rent − Annual Costs) ÷ Total Investment) × 100
Cash-on-Cash ROI = (Annual Net Cashflow ÷ Cash Invested) × 100
// Total Investment includes purchase price + all acquisition costs
Mortgage / Annuity Payment
Monthly Payment = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
// P = principal · r = monthly rate · n = term in months
// Used where a calculator models amortising debt, including UK Rent vs Buy, US mortgage affordability and Polish Kredyt vs Wynajem
UK SDLT — Banded Calculation
SDLT = Σ (Band Rate × Amount in Band)
e.g. £500k additional property in England/Northern Ireland (from 1 April 2025):
£0–125k @ 5% = £6,250
£125–250k @ 7% = £8,750
£250–500k @ 10% = £25,000
Total SDLT = £40,000
// Additional-property rates shown are the standard residential rates plus 5 percentage points. Source: HMRC SDLT guidance
UK Section 24 — Personal vs Ltd Co Tax
Personal: income-tax reduction = 20% × the lowest applicable amount under Section 24
Ltd Co: Tax = (Rent − All Costs incl. Interest) × Corporation Tax Rate
Annual Saving = Personal Tax − (Ltd Co Tax + Dividend Tax on Extraction)
// The reduction is limited by finance costs, property profits and adjusted total income. Source: Finance Act 2015 s.24 · HMRC
DE AfA (Depreciation)
Linear AfA = Building Value × Annual Rate
Pre-1925: 2.5%/yr · 1925+: 2.0%/yr · New build 2023+: 3.0%/yr
Declining Balance (§7 Abs.5a): 5%/yr on remaining book value
Special §7b: +5%/yr years 1–4 (EH40 standard only)
// Source: §7 Abs.4 EStG · §7 Abs.5a EStG · §7b EStG
FR Plus-value — Holding Period Allowances
IR allowance: 6%/yr years 6–21, 4% year 22 → 100% (exempt after yr 22)
PS allowance: 1.65%/yr years 6–21, 1.60% yr 22, 9%/yr years 23–30 → 100%
Tax = PV Nette IR × 19% + PV Nette PS × 17.2%
// Source: CGI art.150 U–150 VH · LF 2025 art. 84 (réintégration des amortissements LMNP)
US MACRS Depreciation (Schedule E)
Full-year baseline depreciation = Building Value ÷ 27.5 years
Year 1: partial year based on mid-month convention
Tax Saving = Depreciation × Marginal Tax Rate
// Source: IRS Publication 946 · IRC §168 · 27.5-year residential MACRS
Legislative sources

Primary sources by market

These are the primary documents used across the market calculators. The calculator index below identifies the principal source or approach for each tool.

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United Kingdom
  • HMRC SDLT guidance (post Oct 2024)
  • Finance Act 2015 — Section 24
  • PRA Supervisory Statement SS13/16 (ICR)
  • Corporation Tax Act 2010
  • HMRC Capital Gains Tax guidance
  • Housing Act 2004 (HMO licensing)
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United States
  • IRS Publication 946 (MACRS depreciation)
  • IRC §168 (cost recovery)
  • HUD/FHA guidelines (MIP, DTI limits)
  • VA Lender Handbook (funding fee)
  • CFPB mortgage disclosure rules
  • State transfer tax schedules (all 50 states)
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Poland
  • Ustawa o PIT — art. 6 ust. 1a (ryczałt 8.5%/12.5%)
  • Ustawa o podatku od czynności cywilnoprawnych (PCC)
  • Rozporządzenie w sprawie maksymalnych stawek taksy notarialnej
  • Ustawa o kosztach sądowych w sprawach cywilnych
  • NBP — loan rate data (WIBOR)
  • GUS — rental market indicators
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Germany
  • GrEStG (Grunderwerbsteuergesetz) — all 16 Länder
  • §7 Abs.4 EStG (lineare AfA)
  • §7 Abs.5a EStG (degressive AfA)
  • §7b EStG (Sonder-AfA Neubau)
  • GNotKG (Notargebühren)
  • §656c BGB (Bestellerprinzip)
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France
  • CGI art. 150 U–150 VH (plus-values immobilières)
  • CGI art. 32 (micro-foncier)
  • Loi n° 2025-127 du 14 février 2025 — art. 84
  • BOFiP — documentation LMNP au régime réel
  • Barème progressif de l’impôt sur le revenu 2026 — 5 tranches
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Switzerland
  • DBG art. 33 (Schuldzinsenabzug, Säule 3a)
  • StHG (Steuerharmonisierungsgesetz)
  • Volksabstimmung 28.09.2025 (Eigenmietwert)
  • OFAS — Säule 3a Limite 2026: CHF 7.258
  • FINMA — Tragbarkeitsregeln (5% stress rate)
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Spain
  • TRLITPAJD RDLeg 1/1993 (ITP, AJD)
  • Ley 5/2019 de Crédito Inmobiliario (AJD banco)
  • AEAT — ITP rates all 19 CCAA (2026)
  • RD 1426/1989 (aranceles notariales)
  • RD 1427/1989 (aranceles registrales)
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Italy
  • Art. 3 D.Lgs. 23/2011 (cedolare secca)
  • DPR 917/1986 TUIR (IRPEF, scaglioni 2026)
  • Legge di Bilancio 2024 (affitti brevi 26%)
  • D.Lgs. 23/2011 art.9 (IMU base imponibile)
  • Agenzia delle Entrate Circolare 26/E/2011
Update policy

When calculators are updated

Calculators are updated when the underlying legislation or source data changes — not on a fixed publishing schedule. Typical review triggers are:

Immediate

Rate changes

Any change to a tax rate, band threshold or official levy — SDLT, GrESt, ITP rates, IRPEF scaglioni, Pilier 3a limits. Updated within days.

Within 30 days

New legislation

Laws that alter the calculation structure — e.g. LF 2025 LMNP reintegration, UK Oct 2024 BTL surcharge, Italian Legge di Bilancio 2024.

Quarterly

Routine review

Each market is reviewed quarterly against official sources to catch minor changes, new guidance or court decisions that affect results.

Known limitations

What calculators do not cover

Being transparent about limitations is as important as being accurate about what is covered.

  • Scotland and Wales (UK): UK calculators apply to England and Northern Ireland only. Scotland uses LBTT and Wales uses LTT — different structures with different rates.
  • German municipal Grundsteuer: the DE Renditerechner uses an illustrative Grundsteuer figure. The actual amount depends on Bodenrichtwert and the local Hebesatz, which varies by Gemeinde.
  • French SCI IS exit tax: the complex double-taxation on SCI IS exit (IS on accounting gain + PFU/IR on dividends) is modelled at standard rates. Actual liability depends on retained earnings history and individual tax position.
  • Swiss cantonal tax rates: CH calculators use a composite Grenzsteuersatz input. Actual rates vary by canton, commune and family situation — Zurich ≠ Geneva ≠ Zug.
  • Spanish CCAA variations: ITP reduced rates (young buyers, large families, disability) are listed but the eligibility conditions vary by CCAA and are not automatically applied.
  • US state income taxes: the US Rental ROI calculator models federal tax (Schedule E) only. State income taxes on rental income are not included — they range from 0% (TX, FL) to 13.3% (CA).
  • Inheritance and gift tax: no market's calculators model succession scenarios — a separate calculation type not yet built.
Calculator index

All 36 calculators and their main inputs

The index below identifies the core formula, assumption set or source used by each tool. Calculator pages may provide fuller methodology or explanatory guidance.

Market Calculator Key sources
🇬🇧 UK BTL Rental Yield HMRC · PRA SS13/16 · Finance Act 2015
🇬🇧 UK Stamp Duty (SDLT) HMRC SDLT guidance · Oct 2024 rates
🇬🇧 UK · Scotland Land and Buildings Transaction Tax (LBTT) Revenue Scotland · Scottish Government LBTT and ADS guidance
🇬🇧 UK · Wales Land Transaction Tax (LTT) Welsh Revenue Authority · LTT rates and higher-rates guidance
🇬🇧 UK Flip Profit HMRC CGT · Finance Act 2015
🇬🇧 UK HMO Yield Housing Act 2004 · HMRC
🇬🇧 UK Section 24 / Ltd Co Finance Act 2015 §24 · CTA 2010
🇬🇧 UK Rent vs Buy HMRC SDLT · Bank of England base rate
🇺🇸 US Mortgage Affordability HUD/FHA guidelines · VA Handbook · CFPB
🇺🇸 US Rental Property ROI IRS Pub. 946 · IRC §168 (MACRS)
🇺🇸 US Closing Costs State transfer tax schedules · CFPB
🇺🇸 US Rent vs Buy CFPB · FHFA House Price Index · BLS rent indexes
🇺🇸 US · ES Calculadora de Hipoteca HUD/FHA guidance · VA Handbook · CFPB
🇺🇸 US · ES ROI Propiedad de Alquiler IRS rental-income and depreciation guidance
🇺🇸 US · ES ¿Alquilar o Comprar? CFPB · FHFA · BLS
🇵🇱 PL Koszty Zakupu Nieruchomości MF: PCC i zwolnienia · taksa notarialna · koszty sądowe
🇵🇱 PL Kalkulator PIT-39 Ustawa o PIT art. 10, 21 i 30e · Ministerstwo Finansów
🇵🇱 PL Kredyt vs Wynajem Ustawa o PIT · NBP (WIBOR)
🇵🇱 PL · UKR Іпотека чи оренда Ustawa o PIT · NBP (WIBOR)
🇵🇱 PL · BEL Пазыка ці арэнда Ustawa o PIT · NBP (WIBOR)
🇵🇱 PL Rentowność Najmu Ustawa o PIT art. 6 ust. 1a (ryczałt)
🇵🇱 PL Pakiet Inwestora Ustawa o PIT · GUS market prices 2026
🇵🇱 PL Estymator Kosztów Remontu GUS construction-cost data · local contractor benchmarks
🇵🇱 PL Porównywarka Nieruchomości Ustawa o PIT · GUS market data
🇩🇪 DE Grunderwerbsteuer GrEStG · GNotKG · §656c BGB
🇩🇪 DE Renditerechner §7 EStG · §21 EStG · GrEStG
🇩🇪 DE AfA-Rechner §7 Abs.4 · §7 Abs.5a · §7b EStG
🇫🇷 FR Rendement Locatif LMNP CGI · Loi n° 2025-127, art. 84 · BOFiP
🇫🇷 FR Plus-value Immobilière CGI art.150 U · Loi n° 2025-127, art. 84
🇫🇷 FR LMNP au réel CGI art. 39 C, 50-0 and 155 IV · DGFiP
🇫🇷 FR Micro-foncier vs réel DGFiP · BOFiP micro-foncier guidance
🇫🇷 FR SCI à l’IR vs à l’IS DGFiP SCI guidance · Service-Public corporation-tax rates
🇨🇭 CH Amortissement FR DBG art.33 · OFAS · Votation 28.09.2025
🇨🇭 CH Amortisation DE DBG art.33 · StHG · BSV
🇪🇸 ES Calculadora ITP TRLITPAJD · Ley 5/2019 · AEAT 2026
🇮🇹 IT Cedolare Secca vs IRPEF D.Lgs.23/2011 · TUIR · LdB 2024
Transparency

Why publish the methodology?

Because a calculator you can't verify is just a black box. Every formula is published openly — both here and inside each individual calculator. If you spot an error or a rate that needs updating, email us.

All content is free to reference and cite for informational purposes. Results are estimates — not financial, tax or legal advice. Always consult a qualified professional before making property decisions.

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